156 lines
6.1 KiB
C++
156 lines
6.1 KiB
C++
// Copyright 2017 The Abseil Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#include "absl/base/internal/thread_identity.h"
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#ifndef _WIN32
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#include <pthread.h>
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#include <signal.h>
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#endif
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#include <atomic>
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#include <cassert>
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#include <memory>
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#include "absl/base/attributes.h"
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#include "absl/base/call_once.h"
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#include "absl/base/internal/raw_logging.h"
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#include "absl/base/internal/spinlock.h"
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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namespace base_internal {
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#if ABSL_THREAD_IDENTITY_MODE != ABSL_THREAD_IDENTITY_MODE_USE_CPP11
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namespace {
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// Used to co-ordinate one-time creation of our pthread_key
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absl::once_flag init_thread_identity_key_once;
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pthread_key_t thread_identity_pthread_key;
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std::atomic<bool> pthread_key_initialized(false);
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void AllocateThreadIdentityKey(ThreadIdentityReclaimerFunction reclaimer) {
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pthread_key_create(&thread_identity_pthread_key, reclaimer);
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pthread_key_initialized.store(true, std::memory_order_release);
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}
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} // namespace
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#endif
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#if ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_TLS || \
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ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_CPP11
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// The actual TLS storage for a thread's currently associated ThreadIdentity.
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// This is referenced by inline accessors in the header.
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// "protected" visibility ensures that if multiple instances of Abseil code
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// exist within a process (via dlopen() or similar), references to
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// thread_identity_ptr from each instance of the code will refer to
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// *different* instances of this ptr.
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// Apple platforms have the visibility attribute, but issue a compile warning
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// that protected visibility is unsupported.
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#if ABSL_HAVE_ATTRIBUTE(visibility) && !defined(__APPLE__)
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__attribute__((visibility("protected")))
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#endif // ABSL_HAVE_ATTRIBUTE(visibility) && !defined(__APPLE__)
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#if ABSL_PER_THREAD_TLS
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// Prefer __thread to thread_local as benchmarks indicate it is a bit faster.
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ABSL_PER_THREAD_TLS_KEYWORD ThreadIdentity* thread_identity_ptr = nullptr;
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#elif defined(ABSL_HAVE_THREAD_LOCAL)
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thread_local ThreadIdentity* thread_identity_ptr = nullptr;
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#endif // ABSL_PER_THREAD_TLS
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#endif // TLS or CPP11
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void SetCurrentThreadIdentity(
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ThreadIdentity* identity, ThreadIdentityReclaimerFunction reclaimer) {
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assert(CurrentThreadIdentityIfPresent() == nullptr);
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// Associate our destructor.
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// NOTE: This call to pthread_setspecific is currently the only immovable
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// barrier to CurrentThreadIdentity() always being async signal safe.
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#if ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_POSIX_SETSPECIFIC
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// NOTE: Not async-safe. But can be open-coded.
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absl::call_once(init_thread_identity_key_once, AllocateThreadIdentityKey,
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reclaimer);
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#if defined(__EMSCRIPTEN__) || defined(__MINGW32__)
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// Emscripten and MinGW pthread implementations does not support signals.
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// See https://kripken.github.io/emscripten-site/docs/porting/pthreads.html
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// for more information.
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pthread_setspecific(thread_identity_pthread_key,
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reinterpret_cast<void*>(identity));
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#else
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// We must mask signals around the call to setspecific as with current glibc,
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// a concurrent getspecific (needed for GetCurrentThreadIdentityIfPresent())
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// may zero our value.
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//
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// While not officially async-signal safe, getspecific within a signal handler
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// is otherwise OK.
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sigset_t all_signals;
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sigset_t curr_signals;
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sigfillset(&all_signals);
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pthread_sigmask(SIG_SETMASK, &all_signals, &curr_signals);
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pthread_setspecific(thread_identity_pthread_key,
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reinterpret_cast<void*>(identity));
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pthread_sigmask(SIG_SETMASK, &curr_signals, nullptr);
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#endif // !__EMSCRIPTEN__ && !__MINGW32__
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#elif ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_TLS
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// NOTE: Not async-safe. But can be open-coded.
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absl::call_once(init_thread_identity_key_once, AllocateThreadIdentityKey,
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reclaimer);
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pthread_setspecific(thread_identity_pthread_key,
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reinterpret_cast<void*>(identity));
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thread_identity_ptr = identity;
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#elif ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_CPP11
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thread_local std::unique_ptr<ThreadIdentity, ThreadIdentityReclaimerFunction>
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holder(identity, reclaimer);
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thread_identity_ptr = identity;
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#else
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#error Unimplemented ABSL_THREAD_IDENTITY_MODE
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#endif
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}
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#if ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_TLS || \
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ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_CPP11
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// Please see the comment on `CurrentThreadIdentityIfPresent` in
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// thread_identity.h. When we cannot expose thread_local variables in
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// headers, we opt for the correct-but-slower option of not inlining this
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// function.
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#ifndef ABSL_INTERNAL_INLINE_CURRENT_THREAD_IDENTITY_IF_PRESENT
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ThreadIdentity* CurrentThreadIdentityIfPresent() { return thread_identity_ptr; }
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#endif
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#endif
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void ClearCurrentThreadIdentity() {
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#if ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_TLS || \
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ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_CPP11
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thread_identity_ptr = nullptr;
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#elif ABSL_THREAD_IDENTITY_MODE == \
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ABSL_THREAD_IDENTITY_MODE_USE_POSIX_SETSPECIFIC
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// pthread_setspecific expected to clear value on destruction
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assert(CurrentThreadIdentityIfPresent() == nullptr);
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#endif
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}
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#if ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_POSIX_SETSPECIFIC
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ThreadIdentity* CurrentThreadIdentityIfPresent() {
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bool initialized = pthread_key_initialized.load(std::memory_order_acquire);
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if (!initialized) {
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return nullptr;
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}
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return reinterpret_cast<ThreadIdentity*>(
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pthread_getspecific(thread_identity_pthread_key));
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}
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#endif
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} // namespace base_internal
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ABSL_NAMESPACE_END
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} // namespace absl
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