blob: f27f16dab59b4def1aa8eeb175a75d9c6db13d08 [file] [log] [blame]
// Copyright 2017 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
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
#include <stdint.h>
#include <new>
// This file is a no-op if the required LowLevelAlloc support is missing.
#include "absl/base/internal/low_level_alloc.h"
#include <string.h>
#include "absl/base/attributes.h"
#include "absl/base/internal/spinlock.h"
#include "absl/base/internal/thread_identity.h"
#include "absl/synchronization/internal/per_thread_sem.h"
namespace absl {
inline namespace lts_2018_12_18 {
namespace synchronization_internal {
// ThreadIdentity storage is persistent, we maintain a free-list of previously
// released ThreadIdentity objects.
static base_internal::SpinLock freelist_lock(base_internal::kLinkerInitialized);
static base_internal::ThreadIdentity* thread_identity_freelist;
// A per-thread destructor for reclaiming associated ThreadIdentity objects.
// Since we must preserve their storage we cache them for re-use.
static void ReclaimThreadIdentity(void* v) {
base_internal::ThreadIdentity* identity =
// all_locks might have been allocated by the Mutex implementation.
// We free it here when we are notified that our thread is dying.
if (identity->per_thread_synch.all_locks != nullptr) {
// We must explicitly clear the current thread's identity:
// (a) Subsequent (unrelated) per-thread destructors may require an identity.
// We must guarantee a new identity is used in this case (this instructor
// will be reinvoked up to PTHREAD_DESTRUCTOR_ITERATIONS in this case).
// (b) ThreadIdentity implementations may depend on memory that is not
// reinitialized before reuse. We must allow explicit clearing of the
// association state in this case.
base_internal::SpinLockHolder l(&freelist_lock);
identity->next = thread_identity_freelist;
thread_identity_freelist = identity;
// Return value rounded up to next multiple of align.
// Align must be a power of two.
static intptr_t RoundUp(intptr_t addr, intptr_t align) {
return (addr + align - 1) & ~(align - 1);
static base_internal::ThreadIdentity* NewThreadIdentity() {
base_internal::ThreadIdentity* identity = nullptr;
// Re-use a previously released object if possible.
base_internal::SpinLockHolder l(&freelist_lock);
if (thread_identity_freelist) {
identity = thread_identity_freelist; // Take list-head.
thread_identity_freelist = thread_identity_freelist->next;
if (identity == nullptr) {
// Allocate enough space to align ThreadIdentity to a multiple of
// PerThreadSynch::kAlignment. This space is never released (it is
// added to a freelist by ReclaimThreadIdentity instead).
void* allocation = base_internal::LowLevelAlloc::Alloc(
sizeof(*identity) + base_internal::PerThreadSynch::kAlignment - 1);
// Round up the address to the required alignment.
identity = reinterpret_cast<base_internal::ThreadIdentity*>(
memset(identity, 0, sizeof(*identity));
return identity;
// Allocates and attaches ThreadIdentity object for the calling thread. Returns
// the new identity.
// REQUIRES: CurrentThreadIdentity(false) == nullptr
base_internal::ThreadIdentity* CreateThreadIdentity() {
base_internal::ThreadIdentity* identity = NewThreadIdentity();
// Associate the value with the current thread, and attach our destructor.
base_internal::SetCurrentThreadIdentity(identity, ReclaimThreadIdentity);
return identity;
} // namespace synchronization_internal
} // inline namespace lts_2018_12_18
} // namespace absl