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Diffstat (limited to 'abseil-cpp/absl/strings/internal/cordz_handle.cc')
-rw-r--r-- | abseil-cpp/absl/strings/internal/cordz_handle.cc | 165 |
1 files changed, 165 insertions, 0 deletions
diff --git a/abseil-cpp/absl/strings/internal/cordz_handle.cc b/abseil-cpp/absl/strings/internal/cordz_handle.cc new file mode 100644 index 0000000..a7061db --- /dev/null +++ b/abseil-cpp/absl/strings/internal/cordz_handle.cc @@ -0,0 +1,165 @@ +// Copyright 2019 The Abseil Authors. +// +// Licensed under the Apache License, Version 2.0 (the "License"); +// you may not use this file except in compliance with the License. +// You may obtain a copy of the License at +// +// https://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, software +// distributed under the License is distributed on an "AS IS" BASIS, +// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +// See the License for the specific language governing permissions and +// limitations under the License. +#include "absl/strings/internal/cordz_handle.h" + +#include <atomic> + +#include "absl/base/internal/raw_logging.h" // For ABSL_RAW_CHECK +#include "absl/synchronization/mutex.h" + +namespace absl { +ABSL_NAMESPACE_BEGIN +namespace cord_internal { + +namespace { + +struct Queue { + Queue() = default; + + absl::Mutex mutex; + std::atomic<CordzHandle*> dq_tail ABSL_GUARDED_BY(mutex){nullptr}; + + // Returns true if this delete queue is empty. This method does not acquire + // the lock, but does a 'load acquire' observation on the delete queue tail. + // It is used inside Delete() to check for the presence of a delete queue + // without holding the lock. The assumption is that the caller is in the + // state of 'being deleted', and can not be newly discovered by a concurrent + // 'being constructed' snapshot instance. Practically, this means that any + // such discovery (`find`, 'first' or 'next', etc) must have proper 'happens + // before / after' semantics and atomic fences. + bool IsEmpty() const ABSL_NO_THREAD_SAFETY_ANALYSIS { + return dq_tail.load(std::memory_order_acquire) == nullptr; + } +}; + +static Queue* GlobalQueue() { + static Queue* global_queue = new Queue; + return global_queue; +} + +} // namespace + +CordzHandle::CordzHandle(bool is_snapshot) : is_snapshot_(is_snapshot) { + Queue* global_queue = GlobalQueue(); + if (is_snapshot) { + MutexLock lock(&global_queue->mutex); + CordzHandle* dq_tail = + global_queue->dq_tail.load(std::memory_order_acquire); + if (dq_tail != nullptr) { + dq_prev_ = dq_tail; + dq_tail->dq_next_ = this; + } + global_queue->dq_tail.store(this, std::memory_order_release); + } +} + +CordzHandle::~CordzHandle() { + Queue* global_queue = GlobalQueue(); + if (is_snapshot_) { + std::vector<CordzHandle*> to_delete; + { + MutexLock lock(&global_queue->mutex); + CordzHandle* next = dq_next_; + if (dq_prev_ == nullptr) { + // We were head of the queue, delete every CordzHandle until we reach + // either the end of the list, or a snapshot handle. + while (next && !next->is_snapshot_) { + to_delete.push_back(next); + next = next->dq_next_; + } + } else { + // Another CordzHandle existed before this one, don't delete anything. + dq_prev_->dq_next_ = next; + } + if (next) { + next->dq_prev_ = dq_prev_; + } else { + global_queue->dq_tail.store(dq_prev_, std::memory_order_release); + } + } + for (CordzHandle* handle : to_delete) { + delete handle; + } + } +} + +bool CordzHandle::SafeToDelete() const { + return is_snapshot_ || GlobalQueue()->IsEmpty(); +} + +void CordzHandle::Delete(CordzHandle* handle) { + assert(handle); + if (handle) { + Queue* const queue = GlobalQueue(); + if (!handle->SafeToDelete()) { + MutexLock lock(&queue->mutex); + CordzHandle* dq_tail = queue->dq_tail.load(std::memory_order_acquire); + if (dq_tail != nullptr) { + handle->dq_prev_ = dq_tail; + dq_tail->dq_next_ = handle; + queue->dq_tail.store(handle, std::memory_order_release); + return; + } + } + delete handle; + } +} + +std::vector<const CordzHandle*> CordzHandle::DiagnosticsGetDeleteQueue() { + std::vector<const CordzHandle*> handles; + Queue* global_queue = GlobalQueue(); + MutexLock lock(&global_queue->mutex); + CordzHandle* dq_tail = global_queue->dq_tail.load(std::memory_order_acquire); + for (const CordzHandle* p = dq_tail; p; p = p->dq_prev_) { + handles.push_back(p); + } + return handles; +} + +bool CordzHandle::DiagnosticsHandleIsSafeToInspect( + const CordzHandle* handle) const { + if (!is_snapshot_) return false; + if (handle == nullptr) return true; + if (handle->is_snapshot_) return false; + bool snapshot_found = false; + Queue* global_queue = GlobalQueue(); + MutexLock lock(&global_queue->mutex); + for (const CordzHandle* p = global_queue->dq_tail; p; p = p->dq_prev_) { + if (p == handle) return !snapshot_found; + if (p == this) snapshot_found = true; + } + ABSL_ASSERT(snapshot_found); // Assert that 'this' is in delete queue. + return true; +} + +std::vector<const CordzHandle*> +CordzHandle::DiagnosticsGetSafeToInspectDeletedHandles() { + std::vector<const CordzHandle*> handles; + if (!is_snapshot()) { + return handles; + } + + Queue* global_queue = GlobalQueue(); + MutexLock lock(&global_queue->mutex); + for (const CordzHandle* p = dq_next_; p != nullptr; p = p->dq_next_) { + if (!p->is_snapshot()) { + handles.push_back(p); + } + } + return handles; +} + +} // namespace cord_internal +ABSL_NAMESPACE_END +} // namespace absl |