Merge remote-tracking branch 'origin/upstream'platform-tools-34.0.5simpleperf-release

Import b/310600229

26 files changed, 1891 insertions, 0 deletions

diff --git a/.cargo_vcs_info.json b/.cargo_vcs_info.json
new file mode 100644
index 0000000..bb0c99d
--- /dev/null
+++ b/.cargo_vcs_info.json
@@ -0,0 +1,6 @@
+{
+  "git": {
+    "sha1": "77a27e9919647956516a2fca32ce52e8e1a5ca53"
+  },
+  "path_in_vcs": ""
+}
\ No newline at end of file
diff --git a/.github/FUNDING.yml b/.github/FUNDING.yml
new file mode 100644
index 0000000..7b47c03
--- /dev/null
+++ b/.github/FUNDING.yml
@@ -0,0 +1 @@
+github: [mitsuhiko]
diff --git a/.github/workflows/clippy.yml b/.github/workflows/clippy.yml
new file mode 100644
index 0000000..e812a0e
--- /dev/null
+++ b/.github/workflows/clippy.yml
@@ -0,0 +1,18 @@
+name: Clippy
+
+on: [push]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v1
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: stable
+          profile: minimal
+          components: clippy, rustfmt
+          override: true
+      - name: Run clippy
+        run: make lint
diff --git a/.github/workflows/rustfmt.yml b/.github/workflows/rustfmt.yml
new file mode 100644
index 0000000..9002962
--- /dev/null
+++ b/.github/workflows/rustfmt.yml
@@ -0,0 +1,18 @@
+name: Rustfmt
+
+on: [push]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v1
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: stable
+          profile: minimal
+          components: clippy, rustfmt
+          override: true
+      - name: Run rustfmt
+        run: make format-check
diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
new file mode 100644
index 0000000..68917f1
--- /dev/null
+++ b/.github/workflows/tests.yml
@@ -0,0 +1,32 @@
+name: Tests
+
+on: [push]
+
+jobs:
+  test-latest:
+    name: Test on Latest
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v1
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: stable
+          profile: minimal
+          override: true
+      - name: Test
+        run: make test
+
+  test-stable:
+    name: Test on 1.42.0
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v1
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: 1.42.0
+          profile: minimal
+          override: true
+      - name: Test
+        run: make test
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..a821aa9
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,4 @@
+
+/target
+**/*.rs.bk
+Cargo.lock
diff --git a/.vscode/settings.json b/.vscode/settings.json
new file mode 100644
index 0000000..edd1e96
--- /dev/null
+++ b/.vscode/settings.json
@@ -0,0 +1,3 @@
+{
+    "rust-analyzer.checkOnSave.command": "clippy"
+}
\ No newline at end of file
diff --git a/Android.bp b/Android.bp
new file mode 100644
index 0000000..e7c3447
--- /dev/null
+++ b/Android.bp
@@ -0,0 +1,34 @@
+// This file is generated by cargo_embargo.
+// Do not modify this file as changes will be overridden on upgrade.
+
+rust_test {
+    name: "fragile_test_src_lib",
+    host_supported: true,
+    crate_name: "fragile",
+    cargo_env_compat: true,
+    cargo_pkg_version: "2.0.0",
+    srcs: ["src/lib.rs"],
+    test_suites: ["general-tests"],
+    auto_gen_config: true,
+    test_options: {
+        unit_test: true,
+    },
+    edition: "2018",
+}
+
+rust_library {
+    name: "libfragile",
+    host_supported: true,
+    crate_name: "fragile",
+    cargo_env_compat: true,
+    cargo_pkg_version: "2.0.0",
+    srcs: ["src/lib.rs"],
+    edition: "2018",
+    apex_available: [
+        "//apex_available:platform",
+        "//apex_available:anyapex",
+    ],
+    product_available: true,
+    vendor_available: true,
+    visibility: ["//external/rust/crates/mockall"],
+}
diff --git a/CHANGELOG.md b/CHANGELOG.md
new file mode 100644
index 0000000..e200b76
--- /dev/null
+++ b/CHANGELOG.md
@@ -0,0 +1,30 @@
+# Changelog
+
+All notable changes to similar are documented here.
+
+## 2.0.0
+
+* `Fragile` no longer boxes internally.
+* `Sticky` and `SemiSticky` now require the use of stack tokens.
+  For more information see [#26](https://github.com/mitsuhiko/fragile/issues/26)
+* `Sticky` now tries to drop entries from the thread local registry eagerly
+  if it's dropped on the right thread.
+
+## 1.2.1
+
+* Fixed non slab versions only allowing a single sticky.
+
+## 1.2.0
+
+Note on safety: the `Sticky` and `SemiSticky` types allow data to live
+longer than the wrapper type which is why they are now requiring a `'static`
+bound.  Previously it was possible to create a sticky containing a bare
+reference which permitted unsafe access.
+
+* `Sticky` now requires `'static`.
+* Added the `slab` feature for an internal optimization for `Sticky` to use
+  a slab instead of a `HashMap`.
+
+## Older Releases
+
+Older releases were yanked due to the insufficient trait bound on `Sticky`.
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..b33fe1c
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,32 @@
+# THIS FILE IS AUTOMATICALLY GENERATED BY CARGO
+#
+# When uploading crates to the registry Cargo will automatically
+# "normalize" Cargo.toml files for maximal compatibility
+# with all versions of Cargo and also rewrite `path` dependencies
+# to registry (e.g., crates.io) dependencies.
+#
+# If you are reading this file be aware that the original Cargo.toml
+# will likely look very different (and much more reasonable).
+# See Cargo.toml.orig for the original contents.
+
+[package]
+edition = "2018"
+name = "fragile"
+version = "2.0.0"
+authors = ["Armin Ronacher <armin.ronacher@active-4.com>"]
+description = "Provides wrapper types for sending non-send values to other threads."
+homepage = "https://github.com/mitsuhiko/fragile"
+readme = "README.md"
+keywords = [
+    "send",
+    "cell",
+    "non-send",
+    "send-wrapper",
+    "failure",
+]
+license = "Apache-2.0"
+repository = "https://github.com/mitsuhiko/fragile"
+
+[dependencies.slab]
+version = "0.4.5"
+optional = true
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..d645695
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,202 @@
+
+                                 Apache License
+                           Version 2.0, January 2004
+                        http://www.apache.org/licenses/
+
+   TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
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+      any Contribution intentionally submitted for inclusion in the Work
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+      this License, without any additional terms or conditions.
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+      the terms of any separate license agreement you may have executed
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+   8. Limitation of Liability. In no event and under no legal theory,
+      whether in tort (including negligence), contract, or otherwise,
+      unless required by applicable law (such as deliberate and grossly
+      negligent acts) or agreed to in writing, shall any Contributor be
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+      Work (including but not limited to damages for loss of goodwill,
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+      boilerplate notice, with the fields enclosed by brackets "[]"
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+   you may not use this file except in compliance with the License.
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diff --git a/METADATA b/METADATA
new file mode 100644
index 0000000..230b483
--- /dev/null
+++ b/METADATA
@@ -0,0 +1,19 @@
+name: "fragile"
+description: "Provides wrapper types for sending non-send values to other threads."
+third_party {
+  identifier {
+    type: "crates.io"
+    value: "https://crates.io/crates/fragile"
+  }
+  identifier {
+    type: "Archive"
+    value: "https://static.crates.io/crates/fragile/fragile-2.0.0.crate"
+  }
+  version: "2.0.0"
+  license_type: NOTICE
+  last_upgrade_date {
+    year: 2023
+    month: 11
+    day: 6
+  }
+}
diff --git a/MODULE_LICENSE_APACHE2 b/MODULE_LICENSE_APACHE2
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/MODULE_LICENSE_APACHE2
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..08a16cf
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,28 @@
+all: build test
+
+build:
+	@cargo build
+
+check:
+	@cargo check
+
+doc:
+	@cargo doc
+
+test:
+	@cargo test
+	@cargo test --all-features
+
+format:
+	@rustup component add rustfmt 2> /dev/null
+	@cargo fmt --all
+
+format-check:
+	@rustup component add rustfmt 2> /dev/null
+	@cargo fmt --all -- --check
+
+lint:
+	@rustup component add clippy 2> /dev/null
+	@cargo clippy
+
+.PHONY: all check doc test format format-check lint
diff --git a/OWNERS b/OWNERS
new file mode 100644
index 0000000..48bea6e
--- /dev/null
+++ b/OWNERS
@@ -0,0 +1,2 @@
+# Bug component: 688011
+include platform/prebuilts/rust:main:/OWNERS
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..5e93fae
--- /dev/null
+++ b/README.md
@@ -0,0 +1,40 @@
+# Fragile
+
+[![Build Status](https://github.com/mitsuhiko/fragile/workflows/Tests/badge.svg?branch=master)](https://github.com/mitsuhiko/fragile/actions?query=workflow%3ATests)
+[![Crates.io](https://img.shields.io/crates/d/fragile.svg)](https://crates.io/crates/fragile)
+[![License](https://img.shields.io/github/license/mitsuhiko/fragile)](https://github.com/mitsuhiko/fragile/blob/master/LICENSE)
+[![rustc 1.42.0](https://img.shields.io/badge/rust-1.42%2B-orange.svg)](https://img.shields.io/badge/rust-1.42%2B-orange.svg)
+[![Documentation](https://docs.rs/fragile/badge.svg)](https://docs.rs/fragile)
+
+This library provides wrapper types that permit sending non Send types to other
+threads and use runtime checks to ensure safety.
+
+It provides the `Fragile<T>`, `Sticky<T>` and `SemiSticky<T>` types which are
+similar in nature but have different behaviors with regards to how destructors
+are executed.  The `Fragile<T>` will panic if the destructor is called in another
+thread, `Sticky<T>` will temporarily leak the object until the thread shuts down.
+`SemiSticky<T>` is a compromise of the two.  It behaves like `Sticky<T>` but it
+avoids the use of thread local storage if the type does not need `Drop`.
+
+## Example
+
+```rust
+use std::thread;
+
+// creating and using a fragile object in the same thread works
+let val = Fragile::new(true);
+assert_eq!(*val.get(), true);
+assert!(val.try_get().is_ok());
+
+// once send to another thread it stops working
+thread::spawn(move || {
+    assert!(val.try_get().is_err());
+}).join()
+    .unwrap();
+```
+
+## License and Links
+
+- [Documentation](https://docs.rs/fragile/)
+- [Issue Tracker](https://github.com/mitsuhiko/fragile/issues)
+- License: [Apache 2.0](https://github.com/mitsuhiko/fragile/blob/master/LICENSE)
diff --git a/cargo_embargo.json b/cargo_embargo.json
new file mode 100644
index 0000000..0d0e572
--- /dev/null
+++ b/cargo_embargo.json
@@ -0,0 +1,8 @@
+{
+  "tests": true,
+  "module_visibility": {
+    "libfragile": [
+      "//external/rust/crates/mockall"
+    ]
+  }
+}
diff --git a/examples/basic-fragile.rs b/examples/basic-fragile.rs
new file mode 100644
index 0000000..54e33fd
--- /dev/null
+++ b/examples/basic-fragile.rs
@@ -0,0 +1,18 @@
+use std::thread;
+
+use fragile::Fragile;
+
+fn main() {
+    // creating and using a fragile object in the same thread works
+    let val = Fragile::new(true);
+    println!("debug print in same thread: {:?}", &val);
+    println!("try_get in same thread: {:?}", val.try_get());
+
+    // once send to another thread it stops working
+    thread::spawn(move || {
+        println!("debug print in other thread: {:?}", &val);
+        println!("try_get in other thread: {:?}", val.try_get());
+    })
+    .join()
+    .unwrap();
+}
diff --git a/examples/basic-sticky.rs b/examples/basic-sticky.rs
new file mode 100644
index 0000000..e982b1d
--- /dev/null
+++ b/examples/basic-sticky.rs
@@ -0,0 +1,21 @@
+use std::thread;
+
+use fragile::Sticky;
+
+fn main() {
+    fragile::stack_token!(tok);
+
+    // creating and using a fragile object in the same thread works
+    let val = Sticky::new(true);
+    println!("debug print in same thread: {:?}", &val);
+    println!("try_get in same thread: {:?}", val.try_get(tok));
+
+    // once send to another thread it stops working
+    thread::spawn(move || {
+        fragile::stack_token!(tok);
+        println!("debug print in other thread: {:?}", &val);
+        println!("try_get in other thread: {:?}", val.try_get(tok));
+    })
+    .join()
+    .unwrap();
+}
diff --git a/src/errors.rs b/src/errors.rs
new file mode 100644
index 0000000..bf3fb4c
--- /dev/null
+++ b/src/errors.rs
@@ -0,0 +1,14 @@
+use std::error;
+use std::fmt;
+
+/// Returned when borrowing fails.
+#[derive(Debug)]
+pub struct InvalidThreadAccess;
+
+impl fmt::Display for InvalidThreadAccess {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "fragile value accessed from foreign thread")
+    }
+}
+
+impl error::Error for InvalidThreadAccess {}
diff --git a/src/fragile.rs b/src/fragile.rs
new file mode 100644
index 0000000..92eb3d3
--- /dev/null
+++ b/src/fragile.rs
@@ -0,0 +1,326 @@
+use std::cmp;
+use std::fmt;
+use std::mem;
+use std::num::NonZeroUsize;
+
+use crate::errors::InvalidThreadAccess;
+use crate::thread_id;
+use std::mem::ManuallyDrop;
+
+/// A [`Fragile<T>`] wraps a non sendable `T` to be safely send to other threads.
+///
+/// Once the value has been wrapped it can be sent to other threads but access
+/// to the value on those threads will fail.
+///
+/// If the value needs destruction and the fragile wrapper is on another thread
+/// the destructor will panic.  Alternatively you can use
+/// [`Sticky`](crate::Sticky) which is not going to panic but might temporarily
+/// leak the value.
+pub struct Fragile<T> {
+    // ManuallyDrop is necessary because we need to move out of here without running the
+    // Drop code in functions like `into_inner`.
+    value: ManuallyDrop<T>,
+    thread_id: NonZeroUsize,
+}
+
+impl<T> Fragile<T> {
+    /// Creates a new [`Fragile`] wrapping a `value`.
+    ///
+    /// The value that is moved into the [`Fragile`] can be non `Send` and
+    /// will be anchored to the thread that created the object.  If the
+    /// fragile wrapper type ends up being send from thread to thread
+    /// only the original thread can interact with the value.
+    pub fn new(value: T) -> Self {
+        Fragile {
+            value: ManuallyDrop::new(value),
+            thread_id: thread_id::get(),
+        }
+    }
+
+    /// Returns `true` if the access is valid.
+    ///
+    /// This will be `false` if the value was sent to another thread.
+    pub fn is_valid(&self) -> bool {
+        thread_id::get() == self.thread_id
+    }
+
+    #[inline(always)]
+    fn assert_thread(&self) {
+        if !self.is_valid() {
+            panic!("trying to access wrapped value in fragile container from incorrect thread.");
+        }
+    }
+
+    /// Consumes the `Fragile`, returning the wrapped value.
+    ///
+    /// # Panics
+    ///
+    /// Panics if called from a different thread than the one where the
+    /// original value was created.
+    pub fn into_inner(self) -> T {
+        self.assert_thread();
+
+        let mut this = ManuallyDrop::new(self);
+
+        // SAFETY: `this` is not accessed beyond this point, and because it's in a ManuallyDrop its
+        // destructor is not run.
+        unsafe { ManuallyDrop::take(&mut this.value) }
+    }
+
+    /// Consumes the `Fragile`, returning the wrapped value if successful.
+    ///
+    /// The wrapped value is returned if this is called from the same thread
+    /// as the one where the original value was created, otherwise the
+    /// [`Fragile`] is returned as `Err(self)`.
+    pub fn try_into_inner(self) -> Result<T, Self> {
+        if thread_id::get() == self.thread_id {
+            Ok(self.into_inner())
+        } else {
+            Err(self)
+        }
+    }
+
+    /// Immutably borrows the wrapped value.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the calling thread is not the one that wrapped the value.
+    /// For a non-panicking variant, use [`try_get`](Self::try_get).
+    pub fn get(&self) -> &T {
+        self.assert_thread();
+        &*self.value
+    }
+
+    /// Mutably borrows the wrapped value.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the calling thread is not the one that wrapped the value.
+    /// For a non-panicking variant, use [`try_get_mut`](Self::try_get_mut).
+    pub fn get_mut(&mut self) -> &mut T {
+        self.assert_thread();
+        &mut *self.value
+    }
+
+    /// Tries to immutably borrow the wrapped value.
+    ///
+    /// Returns `None` if the calling thread is not the one that wrapped the value.
+    pub fn try_get(&self) -> Result<&T, InvalidThreadAccess> {
+        if thread_id::get() == self.thread_id {
+            Ok(&*self.value)
+        } else {
+            Err(InvalidThreadAccess)
+        }
+    }
+
+    /// Tries to mutably borrow the wrapped value.
+    ///
+    /// Returns `None` if the calling thread is not the one that wrapped the value.
+    pub fn try_get_mut(&mut self) -> Result<&mut T, InvalidThreadAccess> {
+        if thread_id::get() == self.thread_id {
+            Ok(&mut *self.value)
+        } else {
+            Err(InvalidThreadAccess)
+        }
+    }
+}
+
+impl<T> Drop for Fragile<T> {
+    fn drop(&mut self) {
+        if mem::needs_drop::<T>() {
+            if thread_id::get() == self.thread_id {
+                // SAFETY: `ManuallyDrop::drop` cannot be called after this point.
+                unsafe { ManuallyDrop::drop(&mut self.value) };
+            } else {
+                panic!("destructor of fragile object ran on wrong thread");
+            }
+        }
+    }
+}
+
+impl<T> From<T> for Fragile<T> {
+    #[inline]
+    fn from(t: T) -> Fragile<T> {
+        Fragile::new(t)
+    }
+}
+
+impl<T: Clone> Clone for Fragile<T> {
+    #[inline]
+    fn clone(&self) -> Fragile<T> {
+        Fragile::new(self.get().clone())
+    }
+}
+
+impl<T: Default> Default for Fragile<T> {
+    #[inline]
+    fn default() -> Fragile<T> {
+        Fragile::new(T::default())
+    }
+}
+
+impl<T: PartialEq> PartialEq for Fragile<T> {
+    #[inline]
+    fn eq(&self, other: &Fragile<T>) -> bool {
+        *self.get() == *other.get()
+    }
+}
+
+impl<T: Eq> Eq for Fragile<T> {}
+
+impl<T: PartialOrd> PartialOrd for Fragile<T> {
+    #[inline]
+    fn partial_cmp(&self, other: &Fragile<T>) -> Option<cmp::Ordering> {
+        self.get().partial_cmp(other.get())
+    }
+
+    #[inline]
+    fn lt(&self, other: &Fragile<T>) -> bool {
+        *self.get() < *other.get()
+    }
+
+    #[inline]
+    fn le(&self, other: &Fragile<T>) -> bool {
+        *self.get() <= *other.get()
+    }
+
+    #[inline]
+    fn gt(&self, other: &Fragile<T>) -> bool {
+        *self.get() > *other.get()
+    }
+
+    #[inline]
+    fn ge(&self, other: &Fragile<T>) -> bool {
+        *self.get() >= *other.get()
+    }
+}
+
+impl<T: Ord> Ord for Fragile<T> {
+    #[inline]
+    fn cmp(&self, other: &Fragile<T>) -> cmp::Ordering {
+        self.get().cmp(other.get())
+    }
+}
+
+impl<T: fmt::Display> fmt::Display for Fragile<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
+        fmt::Display::fmt(self.get(), f)
+    }
+}
+
+impl<T: fmt::Debug> fmt::Debug for Fragile<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
+        match self.try_get() {
+            Ok(value) => f.debug_struct("Fragile").field("value", value).finish(),
+            Err(..) => {
+                struct InvalidPlaceholder;
+                impl fmt::Debug for InvalidPlaceholder {
+                    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+                        f.write_str("<invalid thread>")
+                    }
+                }
+
+                f.debug_struct("Fragile")
+                    .field("value", &InvalidPlaceholder)
+                    .finish()
+            }
+        }
+    }
+}
+
+// this type is sync because access can only ever happy from the same thread
+// that created it originally.  All other threads will be able to safely
+// call some basic operations on the reference and they will fail.
+unsafe impl<T> Sync for Fragile<T> {}
+
+// The entire point of this type is to be Send
+#[allow(clippy::non_send_fields_in_send_ty)]
+unsafe impl<T> Send for Fragile<T> {}
+
+#[test]
+fn test_basic() {
+    use std::thread;
+    let val = Fragile::new(true);
+    assert_eq!(val.to_string(), "true");
+    assert_eq!(val.get(), &true);
+    assert!(val.try_get().is_ok());
+    thread::spawn(move || {
+        assert!(val.try_get().is_err());
+    })
+    .join()
+    .unwrap();
+}
+
+#[test]
+fn test_mut() {
+    let mut val = Fragile::new(true);
+    *val.get_mut() = false;
+    assert_eq!(val.to_string(), "false");
+    assert_eq!(val.get(), &false);
+}
+
+#[test]
+#[should_panic]
+fn test_access_other_thread() {
+    use std::thread;
+    let val = Fragile::new(true);
+    thread::spawn(move || {
+        val.get();
+    })
+    .join()
+    .unwrap();
+}
+
+#[test]
+fn test_noop_drop_elsewhere() {
+    use std::thread;
+    let val = Fragile::new(true);
+    thread::spawn(move || {
+        // force the move
+        val.try_get().ok();
+    })
+    .join()
+    .unwrap();
+}
+
+#[test]
+fn test_panic_on_drop_elsewhere() {
+    use std::sync::atomic::{AtomicBool, Ordering};
+    use std::sync::Arc;
+    use std::thread;
+    let was_called = Arc::new(AtomicBool::new(false));
+    struct X(Arc<AtomicBool>);
+    impl Drop for X {
+        fn drop(&mut self) {
+            self.0.store(true, Ordering::SeqCst);
+        }
+    }
+    let val = Fragile::new(X(was_called.clone()));
+    assert!(thread::spawn(move || {
+        val.try_get().ok();
+    })
+    .join()
+    .is_err());
+    assert!(!was_called.load(Ordering::SeqCst));
+}
+
+#[test]
+fn test_rc_sending() {
+    use std::rc::Rc;
+    use std::sync::mpsc::channel;
+    use std::thread;
+
+    let val = Fragile::new(Rc::new(true));
+    let (tx, rx) = channel();
+
+    let thread = thread::spawn(move || {
+        assert!(val.try_get().is_err());
+        let here = val;
+        tx.send(here).unwrap();
+    });
+
+    let rv = rx.recv().unwrap();
+    assert!(**rv.get());
+
+    thread.join().unwrap();
+}
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..16edc9d
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,157 @@
+//! This library provides wrapper types that permit sending non `Send` types to
+//! other threads and use runtime checks to ensure safety.
+//!
+//! It provides three types: [`Fragile`] and [`Sticky`] which are similar in nature
+//! but have different behaviors with regards to how destructors are executed and
+//! the extra [`SemiSticky`] type which uses [`Sticky`] if the value has a
+//! destructor and [`Fragile`] if it does not.
+//!
+//! All three types wrap a value and provide a `Send` bound.  Neither of the types permit
+//! access to the enclosed value unless the thread that wrapped the value is attempting
+//! to access it.  The difference between the types starts playing a role once
+//! destructors are involved.
+//!
+//! A [`Fragile`] will actually send the `T` from thread to thread but will only
+//! permit the original thread to invoke the destructor.  If the value gets dropped
+//! in a different thread, the destructor will panic.
+//!
+//! A [`Sticky`] on the other hand does not actually send the `T` around but keeps
+//! it stored in the original thread's thread local storage.  If it gets dropped
+//! in the originating thread it gets cleaned up immediately, otherwise it leaks
+//! until the thread shuts down naturally.  [`Sticky`] because it borrows into the
+//! TLS also requires you to "prove" that you are not doing any funny business with
+//! the borrowed value that lives for longer than the current stack frame which
+//! results in a slightly more complex API.
+//!
+//! There is a third typed called [`SemiSticky`] which shares the API with [`Sticky`]
+//! but internally uses a boxed [`Fragile`] if the type does not actually need a dtor
+//! in which case [`Fragile`] is preferred.
+//!
+//! # Fragile Usage
+//!
+//! [`Fragile`] is the easiest type to use.  It works almost like a cell.
+//!
+//! ```
+//! use std::thread;
+//! use fragile::Fragile;
+//!
+//! // creating and using a fragile object in the same thread works
+//! let val = Fragile::new(true);
+//! assert_eq!(*val.get(), true);
+//! assert!(val.try_get().is_ok());
+//!
+//! // once send to another thread it stops working
+//! thread::spawn(move || {
+//!     assert!(val.try_get().is_err());
+//! }).join()
+//!     .unwrap();
+//! ```
+//!
+//! # Sticky Usage
+//!
+//! [`Sticky`] is similar to [`Fragile`] but because it places the value in the
+//! thread local storage it comes with some extra restrictions to make it sound.
+//! The advantage is it can be dropped from any thread but it comes with extra
+//! restrictions.  In particular it requires that values placed in it are `'static`
+//! and that [`StackToken`]s are used to restrict lifetimes.
+//!
+//! ```
+//! use std::thread;
+//! use fragile::Sticky;
+//!
+//! // creating and using a fragile object in the same thread works
+//! fragile::stack_token!(tok);
+//! let val = Sticky::new(true);
+//! assert_eq!(*val.get(tok), true);
+//! assert!(val.try_get(tok).is_ok());
+//!
+//! // once send to another thread it stops working
+//! thread::spawn(move || {
+//!     fragile::stack_token!(tok);
+//!     assert!(val.try_get(tok).is_err());
+//! }).join()
+//!     .unwrap();
+//! ```
+//!
+//! # Why?
+//!
+//! Most of the time trying to use this crate is going to indicate some code smell.  But
+//! there are situations where this is useful.  For instance you might have a bunch of
+//! non `Send` types but want to work with a `Send` error type.  In that case the non
+//! sendable extra information can be contained within the error and in cases where the
+//! error did not cross a thread boundary yet extra information can be obtained.
+//!
+//! # Drop / Cleanup Behavior
+//!
+//! All types will try to eagerly drop a value if they are dropped on the right thread.
+//! [`Sticky`] and [`SemiSticky`] will however temporarily leak memory until a thread
+//! shuts down if the value is dropped on the wrong thread.  The benefit however is that
+//! if you have that type of situation, and you can live with the consequences, the
+//! type is not panicking.  A [`Fragile`] dropped in the wrong thread will not just panic,
+//! it will effectively also tear down the process because panicking in destructors is
+//! non recoverable.
+//!
+//! # Features
+//!
+//! By default the crate has no dependencies.  Optionally the `slab` feature can
+//! be enabled which optimizes the internal storage of the [`Sticky`] type to
+//! make it use a [`slab`](https://docs.rs/slab/latest/slab/) instead.
+mod errors;
+mod fragile;
+mod registry;
+mod semisticky;
+mod sticky;
+mod thread_id;
+
+use std::marker::PhantomData;
+
+pub use crate::errors::InvalidThreadAccess;
+pub use crate::fragile::Fragile;
+pub use crate::semisticky::SemiSticky;
+pub use crate::sticky::Sticky;
+
+/// A token that is placed to the stack to constrain lifetimes.
+///
+/// For more information about how these work see the documentation of
+/// [`stack_token!`] which is the only way to create this token.
+pub struct StackToken(PhantomData<*const ()>);
+
+impl StackToken {
+    /// Stack tokens must only be created on the stack.
+    #[doc(hidden)]
+    pub unsafe fn __private_new() -> StackToken {
+        // we place a const pointer in there to get a type
+        // that is neither Send nor Sync.
+        StackToken(PhantomData)
+    }
+}
+
+/// Crates a token on the stack with a certain name for semi-sticky.
+///
+/// The argument to the macro is the target name of a local variable
+/// which holds a reference to a stack token.  Because this is the
+/// only way to create such a token, it acts as a proof to [`Sticky`]
+/// or [`SemiSticky`] that can be used to constrain the lifetime of the
+/// return values to the stack frame.
+///
+/// This is necessary as otherwise a [`Sticky`] placed in a [`Box`] and
+/// leaked with [`Box::leak`] (which creates a static lifetime) would
+/// otherwise create a reference with `'static` lifetime.  This is incorrect
+/// as the actual lifetime is constrained to the lifetime of the thread.
+/// For more information see [`issue 26`](https://github.com/mitsuhiko/fragile/issues/26).
+///
+/// ```rust
+/// let sticky = fragile::Sticky::new(true);
+///
+/// // this places a token on the stack.
+/// fragile::stack_token!(my_token);
+///
+/// // the token needs to be passed to `get` and others.
+/// let _ = sticky.get(my_token);
+/// ```
+#[macro_export]
+macro_rules! stack_token {
+    ($name:ident) => {
+        let $name = &unsafe { $crate::StackToken::__private_new() };
+    };
+}
diff --git a/src/registry.rs b/src/registry.rs
new file mode 100644
index 0000000..1ee070d
--- /dev/null
+++ b/src/registry.rs
@@ -0,0 +1,104 @@
+pub struct Entry {
+    /// The pointer to the object stored in the registry. This is a type-erased
+    /// `Box<T>`.
+    pub ptr: *mut (),
+    /// The function that can be called on the above pointer to drop the object
+    /// and free its allocation.
+    pub drop: unsafe fn(*mut ()),
+}
+
+#[cfg(feature = "slab")]
+mod slab_impl {
+    use std::cell::UnsafeCell;
+    use std::num::NonZeroUsize;
+
+    use super::Entry;
+
+    pub struct Registry(pub slab::Slab<Entry>);
+
+    thread_local!(static REGISTRY: UnsafeCell<Registry> = UnsafeCell::new(Registry(slab::Slab::new())));
+
+    pub use usize as ItemId;
+
+    pub fn insert(thread_id: NonZeroUsize, entry: Entry) -> ItemId {
+        let _ = thread_id;
+        REGISTRY.with(|registry| unsafe { (*registry.get()).0.insert(entry) })
+    }
+
+    pub fn with<R, F: FnOnce(&Entry) -> R>(item_id: ItemId, thread_id: NonZeroUsize, f: F) -> R {
+        let _ = thread_id;
+        REGISTRY.with(|registry| f(unsafe { &*registry.get() }.0.get(item_id).unwrap()))
+    }
+
+    pub fn remove(item_id: ItemId, thread_id: NonZeroUsize) -> Entry {
+        let _ = thread_id;
+        REGISTRY.with(|registry| unsafe { (*registry.get()).0.remove(item_id) })
+    }
+
+    pub fn try_remove(item_id: ItemId, thread_id: NonZeroUsize) -> Option<Entry> {
+        let _ = thread_id;
+        REGISTRY.with(|registry| unsafe { (*registry.get()).0.try_remove(item_id) })
+    }
+}
+
+#[cfg(not(feature = "slab"))]
+mod map_impl {
+    use std::cell::UnsafeCell;
+    use std::num::NonZeroUsize;
+    use std::sync::atomic::{AtomicUsize, Ordering};
+
+    use super::Entry;
+
+    pub struct Registry(pub std::collections::HashMap<(NonZeroUsize, NonZeroUsize), Entry>);
+
+    thread_local!(static REGISTRY: UnsafeCell<Registry> = UnsafeCell::new(Registry(Default::default())));
+
+    pub type ItemId = NonZeroUsize;
+
+    fn next_item_id() -> NonZeroUsize {
+        static COUNTER: AtomicUsize = AtomicUsize::new(1);
+        NonZeroUsize::new(COUNTER.fetch_add(1, Ordering::SeqCst))
+            .expect("more than usize::MAX items")
+    }
+
+    pub fn insert(thread_id: NonZeroUsize, entry: Entry) -> ItemId {
+        let item_id = next_item_id();
+        REGISTRY
+            .with(|registry| unsafe { (*registry.get()).0.insert((thread_id, item_id), entry) });
+        item_id
+    }
+
+    pub fn with<R, F: FnOnce(&Entry) -> R>(item_id: ItemId, thread_id: NonZeroUsize, f: F) -> R {
+        REGISTRY.with(|registry| {
+            f(unsafe { &*registry.get() }
+                .0
+                .get(&(thread_id, item_id))
+                .unwrap())
+        })
+    }
+
+    pub fn remove(item_id: ItemId, thread_id: NonZeroUsize) -> Entry {
+        REGISTRY
+            .with(|registry| unsafe { (*registry.get()).0.remove(&(thread_id, item_id)).unwrap() })
+    }
+
+    pub fn try_remove(item_id: ItemId, thread_id: NonZeroUsize) -> Option<Entry> {
+        REGISTRY.with(|registry| unsafe { (*registry.get()).0.remove(&(thread_id, item_id)) })
+    }
+}
+
+#[cfg(feature = "slab")]
+pub use self::slab_impl::*;
+
+#[cfg(not(feature = "slab"))]
+pub use self::map_impl::*;
+
+impl Drop for Registry {
+    fn drop(&mut self) {
+        for (_, value) in self.0.iter() {
+            // SAFETY: This function is only called once, and is called with the
+            // pointer it was created with.
+            unsafe { (value.drop)(value.ptr) };
+        }
+    }
+}
diff --git a/src/semisticky.rs b/src/semisticky.rs
new file mode 100644
index 0000000..2b6c0f4
--- /dev/null
+++ b/src/semisticky.rs
@@ -0,0 +1,339 @@
+use std::cmp;
+use std::fmt;
+use std::mem;
+
+use crate::errors::InvalidThreadAccess;
+use crate::fragile::Fragile;
+use crate::sticky::Sticky;
+use crate::StackToken;
+
+enum SemiStickyImpl<T: 'static> {
+    Fragile(Box<Fragile<T>>),
+    Sticky(Sticky<T>),
+}
+
+/// A [`SemiSticky<T>`] keeps a value T stored in a thread if it has a drop.
+///
+/// This is a combined version of [`Fragile`] and [`Sticky`].  If the type
+/// does not have a drop it will effectively be a [`Fragile`], otherwise it
+/// will be internally behave like a [`Sticky`].
+///
+/// This type requires `T: 'static` for the same reasons as [`Sticky`] and
+/// also uses [`StackToken`]s.
+pub struct SemiSticky<T: 'static> {
+    inner: SemiStickyImpl<T>,
+}
+
+impl<T> SemiSticky<T> {
+    /// Creates a new [`SemiSticky`] wrapping a `value`.
+    ///
+    /// The value that is moved into the `SemiSticky` can be non `Send` and
+    /// will be anchored to the thread that created the object.  If the
+    /// sticky wrapper type ends up being send from thread to thread
+    /// only the original thread can interact with the value.  In case the
+    /// value does not have `Drop` it will be stored in the [`SemiSticky`]
+    /// instead.
+    pub fn new(value: T) -> Self {
+        SemiSticky {
+            inner: if mem::needs_drop::<T>() {
+                SemiStickyImpl::Sticky(Sticky::new(value))
+            } else {
+                SemiStickyImpl::Fragile(Box::new(Fragile::new(value)))
+            },
+        }
+    }
+
+    /// Returns `true` if the access is valid.
+    ///
+    /// This will be `false` if the value was sent to another thread.
+    pub fn is_valid(&self) -> bool {
+        match self.inner {
+            SemiStickyImpl::Fragile(ref inner) => inner.is_valid(),
+            SemiStickyImpl::Sticky(ref inner) => inner.is_valid(),
+        }
+    }
+
+    /// Consumes the [`SemiSticky`], returning the wrapped value.
+    ///
+    /// # Panics
+    ///
+    /// Panics if called from a different thread than the one where the
+    /// original value was created.
+    pub fn into_inner(self) -> T {
+        match self.inner {
+            SemiStickyImpl::Fragile(inner) => inner.into_inner(),
+            SemiStickyImpl::Sticky(inner) => inner.into_inner(),
+        }
+    }
+
+    /// Consumes the [`SemiSticky`], returning the wrapped value if successful.
+    ///
+    /// The wrapped value is returned if this is called from the same thread
+    /// as the one where the original value was created, otherwise the
+    /// [`SemiSticky`] is returned as `Err(self)`.
+    pub fn try_into_inner(self) -> Result<T, Self> {
+        match self.inner {
+            SemiStickyImpl::Fragile(inner) => inner.try_into_inner().map_err(|inner| SemiSticky {
+                inner: SemiStickyImpl::Fragile(Box::new(inner)),
+            }),
+            SemiStickyImpl::Sticky(inner) => inner.try_into_inner().map_err(|inner| SemiSticky {
+                inner: SemiStickyImpl::Sticky(inner),
+            }),
+        }
+    }
+
+    /// Immutably borrows the wrapped value.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the calling thread is not the one that wrapped the value.
+    /// For a non-panicking variant, use [`try_get`](Self::try_get).
+    pub fn get<'stack>(&'stack self, _proof: &'stack StackToken) -> &'stack T {
+        match self.inner {
+            SemiStickyImpl::Fragile(ref inner) => inner.get(),
+            SemiStickyImpl::Sticky(ref inner) => inner.get(_proof),
+        }
+    }
+
+    /// Mutably borrows the wrapped value.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the calling thread is not the one that wrapped the value.
+    /// For a non-panicking variant, use [`try_get_mut`](Self::try_get_mut).
+    pub fn get_mut<'stack>(&'stack mut self, _proof: &'stack StackToken) -> &'stack mut T {
+        match self.inner {
+            SemiStickyImpl::Fragile(ref mut inner) => inner.get_mut(),
+            SemiStickyImpl::Sticky(ref mut inner) => inner.get_mut(_proof),
+        }
+    }
+
+    /// Tries to immutably borrow the wrapped value.
+    ///
+    /// Returns `None` if the calling thread is not the one that wrapped the value.
+    pub fn try_get<'stack>(
+        &'stack self,
+        _proof: &'stack StackToken,
+    ) -> Result<&'stack T, InvalidThreadAccess> {
+        match self.inner {
+            SemiStickyImpl::Fragile(ref inner) => inner.try_get(),
+            SemiStickyImpl::Sticky(ref inner) => inner.try_get(_proof),
+        }
+    }
+
+    /// Tries to mutably borrow the wrapped value.
+    ///
+    /// Returns `None` if the calling thread is not the one that wrapped the value.
+    pub fn try_get_mut<'stack>(
+        &'stack mut self,
+        _proof: &'stack StackToken,
+    ) -> Result<&'stack mut T, InvalidThreadAccess> {
+        match self.inner {
+            SemiStickyImpl::Fragile(ref mut inner) => inner.try_get_mut(),
+            SemiStickyImpl::Sticky(ref mut inner) => inner.try_get_mut(_proof),
+        }
+    }
+}
+
+impl<T> From<T> for SemiSticky<T> {
+    #[inline]
+    fn from(t: T) -> SemiSticky<T> {
+        SemiSticky::new(t)
+    }
+}
+
+impl<T: Clone> Clone for SemiSticky<T> {
+    #[inline]
+    fn clone(&self) -> SemiSticky<T> {
+        crate::stack_token!(tok);
+        SemiSticky::new(self.get(tok).clone())
+    }
+}
+
+impl<T: Default> Default for SemiSticky<T> {
+    #[inline]
+    fn default() -> SemiSticky<T> {
+        SemiSticky::new(T::default())
+    }
+}
+
+impl<T: PartialEq> PartialEq for SemiSticky<T> {
+    #[inline]
+    fn eq(&self, other: &SemiSticky<T>) -> bool {
+        crate::stack_token!(tok);
+        *self.get(tok) == *other.get(tok)
+    }
+}
+
+impl<T: Eq> Eq for SemiSticky<T> {}
+
+impl<T: PartialOrd> PartialOrd for SemiSticky<T> {
+    #[inline]
+    fn partial_cmp(&self, other: &SemiSticky<T>) -> Option<cmp::Ordering> {
+        crate::stack_token!(tok);
+        self.get(tok).partial_cmp(other.get(tok))
+    }
+
+    #[inline]
+    fn lt(&self, other: &SemiSticky<T>) -> bool {
+        crate::stack_token!(tok);
+        *self.get(tok) < *other.get(tok)
+    }
+
+    #[inline]
+    fn le(&self, other: &SemiSticky<T>) -> bool {
+        crate::stack_token!(tok);
+        *self.get(tok) <= *other.get(tok)
+    }
+
+    #[inline]
+    fn gt(&self, other: &SemiSticky<T>) -> bool {
+        crate::stack_token!(tok);
+        *self.get(tok) > *other.get(tok)
+    }
+
+    #[inline]
+    fn ge(&self, other: &SemiSticky<T>) -> bool {
+        crate::stack_token!(tok);
+        *self.get(tok) >= *other.get(tok)
+    }
+}
+
+impl<T: Ord> Ord for SemiSticky<T> {
+    #[inline]
+    fn cmp(&self, other: &SemiSticky<T>) -> cmp::Ordering {
+        crate::stack_token!(tok);
+        self.get(tok).cmp(other.get(tok))
+    }
+}
+
+impl<T: fmt::Display> fmt::Display for SemiSticky<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
+        crate::stack_token!(tok);
+        fmt::Display::fmt(self.get(tok), f)
+    }
+}
+
+impl<T: fmt::Debug> fmt::Debug for SemiSticky<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
+        crate::stack_token!(tok);
+        match self.try_get(tok) {
+            Ok(value) => f.debug_struct("SemiSticky").field("value", value).finish(),
+            Err(..) => {
+                struct InvalidPlaceholder;
+                impl fmt::Debug for InvalidPlaceholder {
+                    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+                        f.write_str("<invalid thread>")
+                    }
+                }
+
+                f.debug_struct("SemiSticky")
+                    .field("value", &InvalidPlaceholder)
+                    .finish()
+            }
+        }
+    }
+}
+
+#[test]
+fn test_basic() {
+    use std::thread;
+    let val = SemiSticky::new(true);
+    crate::stack_token!(tok);
+    assert_eq!(val.to_string(), "true");
+    assert_eq!(val.get(tok), &true);
+    assert!(val.try_get(tok).is_ok());
+    thread::spawn(move || {
+        crate::stack_token!(tok);
+        assert!(val.try_get(tok).is_err());
+    })
+    .join()
+    .unwrap();
+}
+
+#[test]
+fn test_mut() {
+    let mut val = SemiSticky::new(true);
+    crate::stack_token!(tok);
+    *val.get_mut(tok) = false;
+    assert_eq!(val.to_string(), "false");
+    assert_eq!(val.get(tok), &false);
+}
+
+#[test]
+#[should_panic]
+fn test_access_other_thread() {
+    use std::thread;
+    let val = SemiSticky::new(true);
+    thread::spawn(move || {
+        crate::stack_token!(tok);
+        val.get(tok);
+    })
+    .join()
+    .unwrap();
+}
+
+#[test]
+fn test_drop_same_thread() {
+    use std::sync::atomic::{AtomicBool, Ordering};
+    use std::sync::Arc;
+    let was_called = Arc::new(AtomicBool::new(false));
+    struct X(Arc<AtomicBool>);
+    impl Drop for X {
+        fn drop(&mut self) {
+            self.0.store(true, Ordering::SeqCst);
+        }
+    }
+    let val = SemiSticky::new(X(was_called.clone()));
+    mem::drop(val);
+    assert!(was_called.load(Ordering::SeqCst));
+}
+
+#[test]
+fn test_noop_drop_elsewhere() {
+    use std::sync::atomic::{AtomicBool, Ordering};
+    use std::sync::Arc;
+    use std::thread;
+
+    let was_called = Arc::new(AtomicBool::new(false));
+
+    {
+        let was_called = was_called.clone();
+        thread::spawn(move || {
+            struct X(Arc<AtomicBool>);
+            impl Drop for X {
+                fn drop(&mut self) {
+                    self.0.store(true, Ordering::SeqCst);
+                }
+            }
+
+            let val = SemiSticky::new(X(was_called.clone()));
+            assert!(thread::spawn(move || {
+                // moves it here but do not deallocate
+                crate::stack_token!(tok);
+                val.try_get(tok).ok();
+            })
+            .join()
+            .is_ok());
+
+            assert!(!was_called.load(Ordering::SeqCst));
+        })
+        .join()
+        .unwrap();
+    }
+
+    assert!(was_called.load(Ordering::SeqCst));
+}
+
+#[test]
+fn test_rc_sending() {
+    use std::rc::Rc;
+    use std::thread;
+    let val = SemiSticky::new(Rc::new(true));
+    thread::spawn(move || {
+        crate::stack_token!(tok);
+        assert!(val.try_get(tok).is_err());
+    })
+    .join()
+    .unwrap();
+}
diff --git a/src/sticky.rs b/src/sticky.rs
new file mode 100644
index 0000000..bc15c40
--- /dev/null
+++ b/src/sticky.rs
@@ -0,0 +1,423 @@
+#![allow(clippy::unit_arg)]
+
+use std::cmp;
+use std::fmt;
+use std::marker::PhantomData;
+use std::mem;
+use std::num::NonZeroUsize;
+
+use crate::errors::InvalidThreadAccess;
+use crate::registry;
+use crate::thread_id;
+use crate::StackToken;
+
+/// A [`Sticky<T>`] keeps a value T stored in a thread.
+///
+/// This type works similar in nature to [`Fragile`](crate::Fragile) and exposes a
+/// similar interface.  The difference is that whereas [`Fragile`](crate::Fragile) has
+/// its destructor called in the thread where the value was sent, a
+/// [`Sticky`] that is moved to another thread will have the internal
+/// destructor called when the originating thread tears down.
+///
+/// Because [`Sticky`] allows values to be kept alive for longer than the
+/// [`Sticky`] itself, it requires all its contents to be `'static` for
+/// soundness.  More importantly it also requires the use of [`StackToken`]s.
+/// For information about how to use stack tokens and why they are neded,
+/// refer to [`stack_token!`](crate::stack_token).
+///
+/// As this uses TLS internally the general rules about the platform limitations
+/// of destructors for TLS apply.
+pub struct Sticky<T: 'static> {
+    item_id: registry::ItemId,
+    thread_id: NonZeroUsize,
+    _marker: PhantomData<*mut T>,
+}
+
+impl<T> Drop for Sticky<T> {
+    fn drop(&mut self) {
+        // if the type needs dropping we can only do so on the
+        // right thread.  worst case we leak the value until the
+        // thread dies.
+        if mem::needs_drop::<T>() {
+            unsafe {
+                if self.is_valid() {
+                    self.unsafe_take_value();
+                }
+            }
+
+        // otherwise we take the liberty to drop the value
+        // right here and now.  We can however only do that if
+        // we are on the right thread.  If we are not, we again
+        // need to wait for the thread to shut down.
+        } else if let Some(entry) = registry::try_remove(self.item_id, self.thread_id) {
+            unsafe {
+                (entry.drop)(entry.ptr);
+            }
+        }
+    }
+}
+
+impl<T> Sticky<T> {
+    /// Creates a new [`Sticky`] wrapping a `value`.
+    ///
+    /// The value that is moved into the [`Sticky`] can be non `Send` and
+    /// will be anchored to the thread that created the object.  If the
+    /// sticky wrapper type ends up being send from thread to thread
+    /// only the original thread can interact with the value.
+    pub fn new(value: T) -> Self {
+        let entry = registry::Entry {
+            ptr: Box::into_raw(Box::new(value)).cast(),
+            drop: |ptr| {
+                let ptr = ptr.cast::<T>();
+                // SAFETY: This callback will only be called once, with the
+                // above pointer.
+                drop(unsafe { Box::from_raw(ptr) });
+            },
+        };
+
+        let thread_id = thread_id::get();
+        let item_id = registry::insert(thread_id, entry);
+
+        Sticky {
+            item_id,
+            thread_id,
+            _marker: PhantomData,
+        }
+    }
+
+    #[inline(always)]
+    fn with_value<F: FnOnce(*mut T) -> R, R>(&self, f: F) -> R {
+        self.assert_thread();
+
+        registry::with(self.item_id, self.thread_id, |entry| {
+            f(entry.ptr.cast::<T>())
+        })
+    }
+
+    /// Returns `true` if the access is valid.
+    ///
+    /// This will be `false` if the value was sent to another thread.
+    #[inline(always)]
+    pub fn is_valid(&self) -> bool {
+        thread_id::get() == self.thread_id
+    }
+
+    #[inline(always)]
+    fn assert_thread(&self) {
+        if !self.is_valid() {
+            panic!("trying to access wrapped value in sticky container from incorrect thread.");
+        }
+    }
+
+    /// Consumes the `Sticky`, returning the wrapped value.
+    ///
+    /// # Panics
+    ///
+    /// Panics if called from a different thread than the one where the
+    /// original value was created.
+    pub fn into_inner(mut self) -> T {
+        self.assert_thread();
+        unsafe {
+            let rv = self.unsafe_take_value();
+            mem::forget(self);
+            rv
+        }
+    }
+
+    unsafe fn unsafe_take_value(&mut self) -> T {
+        let ptr = registry::remove(self.item_id, self.thread_id)
+            .ptr
+            .cast::<T>();
+        *Box::from_raw(ptr)
+    }
+
+    /// Consumes the `Sticky`, returning the wrapped value if successful.
+    ///
+    /// The wrapped value is returned if this is called from the same thread
+    /// as the one where the original value was created, otherwise the
+    /// `Sticky` is returned as `Err(self)`.
+    pub fn try_into_inner(self) -> Result<T, Self> {
+        if self.is_valid() {
+            Ok(self.into_inner())
+        } else {
+            Err(self)
+        }
+    }
+
+    /// Immutably borrows the wrapped value.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the calling thread is not the one that wrapped the value.
+    /// For a non-panicking variant, use [`try_get`](#method.try_get`).
+    pub fn get<'stack>(&'stack self, _proof: &'stack StackToken) -> &'stack T {
+        self.with_value(|value| unsafe { &*value })
+    }
+
+    /// Mutably borrows the wrapped value.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the calling thread is not the one that wrapped the value.
+    /// For a non-panicking variant, use [`try_get_mut`](#method.try_get_mut`).
+    pub fn get_mut<'stack>(&'stack mut self, _proof: &'stack StackToken) -> &'stack mut T {
+        self.with_value(|value| unsafe { &mut *value })
+    }
+
+    /// Tries to immutably borrow the wrapped value.
+    ///
+    /// Returns `None` if the calling thread is not the one that wrapped the value.
+    pub fn try_get<'stack>(
+        &'stack self,
+        _proof: &'stack StackToken,
+    ) -> Result<&'stack T, InvalidThreadAccess> {
+        if self.is_valid() {
+            Ok(self.with_value(|value| unsafe { &*value }))
+        } else {
+            Err(InvalidThreadAccess)
+        }
+    }
+
+    /// Tries to mutably borrow the wrapped value.
+    ///
+    /// Returns `None` if the calling thread is not the one that wrapped the value.
+    pub fn try_get_mut<'stack>(
+        &'stack mut self,
+        _proof: &'stack StackToken,
+    ) -> Result<&'stack mut T, InvalidThreadAccess> {
+        if self.is_valid() {
+            Ok(self.with_value(|value| unsafe { &mut *value }))
+        } else {
+            Err(InvalidThreadAccess)
+        }
+    }
+}
+
+impl<T> From<T> for Sticky<T> {
+    #[inline]
+    fn from(t: T) -> Sticky<T> {
+        Sticky::new(t)
+    }
+}
+
+impl<T: Clone> Clone for Sticky<T> {
+    #[inline]
+    fn clone(&self) -> Sticky<T> {
+        crate::stack_token!(tok);
+        Sticky::new(self.get(tok).clone())
+    }
+}
+
+impl<T: Default> Default for Sticky<T> {
+    #[inline]
+    fn default() -> Sticky<T> {
+        Sticky::new(T::default())
+    }
+}
+
+impl<T: PartialEq> PartialEq for Sticky<T> {
+    #[inline]
+    fn eq(&self, other: &Sticky<T>) -> bool {
+        crate::stack_token!(tok);
+        *self.get(tok) == *other.get(tok)
+    }
+}
+
+impl<T: Eq> Eq for Sticky<T> {}
+
+impl<T: PartialOrd> PartialOrd for Sticky<T> {
+    #[inline]
+    fn partial_cmp(&self, other: &Sticky<T>) -> Option<cmp::Ordering> {
+        crate::stack_token!(tok);
+        self.get(tok).partial_cmp(other.get(tok))
+    }
+
+    #[inline]
+    fn lt(&self, other: &Sticky<T>) -> bool {
+        crate::stack_token!(tok);
+        *self.get(tok) < *other.get(tok)
+    }
+
+    #[inline]
+    fn le(&self, other: &Sticky<T>) -> bool {
+        crate::stack_token!(tok);
+        *self.get(tok) <= *other.get(tok)
+    }
+
+    #[inline]
+    fn gt(&self, other: &Sticky<T>) -> bool {
+        crate::stack_token!(tok);
+        *self.get(tok) > *other.get(tok)
+    }
+
+    #[inline]
+    fn ge(&self, other: &Sticky<T>) -> bool {
+        crate::stack_token!(tok);
+        *self.get(tok) >= *other.get(tok)
+    }
+}
+
+impl<T: Ord> Ord for Sticky<T> {
+    #[inline]
+    fn cmp(&self, other: &Sticky<T>) -> cmp::Ordering {
+        crate::stack_token!(tok);
+        self.get(tok).cmp(other.get(tok))
+    }
+}
+
+impl<T: fmt::Display> fmt::Display for Sticky<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
+        crate::stack_token!(tok);
+        fmt::Display::fmt(self.get(tok), f)
+    }
+}
+
+impl<T: fmt::Debug> fmt::Debug for Sticky<T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
+        crate::stack_token!(tok);
+        match self.try_get(tok) {
+            Ok(value) => f.debug_struct("Sticky").field("value", value).finish(),
+            Err(..) => {
+                struct InvalidPlaceholder;
+                impl fmt::Debug for InvalidPlaceholder {
+                    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+                        f.write_str("<invalid thread>")
+                    }
+                }
+
+                f.debug_struct("Sticky")
+                    .field("value", &InvalidPlaceholder)
+                    .finish()
+            }
+        }
+    }
+}
+
+// similar as for fragile ths type is sync because it only accesses TLS data
+// which is thread local.  There is nothing that needs to be synchronized.
+unsafe impl<T> Sync for Sticky<T> {}
+
+// The entire point of this type is to be Send
+unsafe impl<T> Send for Sticky<T> {}
+
+#[test]
+fn test_basic() {
+    use std::thread;
+    let val = Sticky::new(true);
+    crate::stack_token!(tok);
+    assert_eq!(val.to_string(), "true");
+    assert_eq!(val.get(tok), &true);
+    assert!(val.try_get(tok).is_ok());
+    thread::spawn(move || {
+        crate::stack_token!(tok);
+        assert!(val.try_get(tok).is_err());
+    })
+    .join()
+    .unwrap();
+}
+
+#[test]
+fn test_mut() {
+    let mut val = Sticky::new(true);
+    crate::stack_token!(tok);
+    *val.get_mut(tok) = false;
+    assert_eq!(val.to_string(), "false");
+    assert_eq!(val.get(tok), &false);
+}
+
+#[test]
+#[should_panic]
+fn test_access_other_thread() {
+    use std::thread;
+    let val = Sticky::new(true);
+    thread::spawn(move || {
+        crate::stack_token!(tok);
+        val.get(tok);
+    })
+    .join()
+    .unwrap();
+}
+
+#[test]
+fn test_drop_same_thread() {
+    use std::sync::atomic::{AtomicBool, Ordering};
+    use std::sync::Arc;
+    let was_called = Arc::new(AtomicBool::new(false));
+    struct X(Arc<AtomicBool>);
+    impl Drop for X {
+        fn drop(&mut self) {
+            self.0.store(true, Ordering::SeqCst);
+        }
+    }
+    let val = Sticky::new(X(was_called.clone()));
+    mem::drop(val);
+    assert!(was_called.load(Ordering::SeqCst));
+}
+
+#[test]
+fn test_noop_drop_elsewhere() {
+    use std::sync::atomic::{AtomicBool, Ordering};
+    use std::sync::Arc;
+    use std::thread;
+
+    let was_called = Arc::new(AtomicBool::new(false));
+
+    {
+        let was_called = was_called.clone();
+        thread::spawn(move || {
+            struct X(Arc<AtomicBool>);
+            impl Drop for X {
+                fn drop(&mut self) {
+                    self.0.store(true, Ordering::SeqCst);
+                }
+            }
+
+            let val = Sticky::new(X(was_called.clone()));
+            assert!(thread::spawn(move || {
+                // moves it here but do not deallocate
+                crate::stack_token!(tok);
+                val.try_get(tok).ok();
+            })
+            .join()
+            .is_ok());
+
+            assert!(!was_called.load(Ordering::SeqCst));
+        })
+        .join()
+        .unwrap();
+    }
+
+    assert!(was_called.load(Ordering::SeqCst));
+}
+
+#[test]
+fn test_rc_sending() {
+    use std::rc::Rc;
+    use std::thread;
+    let val = Sticky::new(Rc::new(true));
+    thread::spawn(move || {
+        crate::stack_token!(tok);
+        assert!(val.try_get(tok).is_err());
+    })
+    .join()
+    .unwrap();
+}
+
+#[test]
+fn test_two_stickies() {
+    struct Wat;
+
+    impl Drop for Wat {
+        fn drop(&mut self) {
+            // do nothing
+        }
+    }
+
+    let s1 = Sticky::new(Wat);
+    let s2 = Sticky::new(Wat);
+
+    // make sure all is well
+
+    drop(s1);
+    drop(s2);
+}
diff --git a/src/thread_id.rs b/src/thread_id.rs
new file mode 100644
index 0000000..00468b2
--- /dev/null
+++ b/src/thread_id.rs
@@ -0,0 +1,12 @@
+use std::num::NonZeroUsize;
+use std::sync::atomic::{AtomicUsize, Ordering};
+
+fn next() -> NonZeroUsize {
+    static COUNTER: AtomicUsize = AtomicUsize::new(1);
+    NonZeroUsize::new(COUNTER.fetch_add(1, Ordering::SeqCst)).expect("more than usize::MAX threads")
+}
+
+pub(crate) fn get() -> NonZeroUsize {
+    thread_local!(static THREAD_ID: NonZeroUsize = next());
+    THREAD_ID.with(|&x| x)
+}