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authorGravatar misterg <misterg@google.com>2017-09-19 16:54:40 -0400
committerGravatar misterg <misterg@google.com>2017-09-19 16:54:40 -0400
commitc2e754829628d1e9b7a16b3389cfdace76950fdf (patch)
tree5a7f056f44e27c30e10025113b644f0b3b5801fc /absl/base/internal/thread_identity.cc
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+// 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
+//
+// http://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/base/internal/thread_identity.h"
+
+#ifndef _WIN32
+#include <pthread.h>
+#include <signal.h>
+#endif
+
+#include <atomic>
+#include <cassert>
+#include <memory>
+
+#include "absl/base/call_once.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/base/internal/spinlock.h"
+
+namespace absl {
+namespace base_internal {
+
+#if ABSL_THREAD_IDENTITY_MODE != ABSL_THREAD_IDENTITY_MODE_USE_CPP11
+namespace {
+// Used to co-ordinate one-time creation of our pthread_key
+absl::once_flag init_thread_identity_key_once;
+pthread_key_t thread_identity_pthread_key;
+std::atomic<bool> pthread_key_initialized(false);
+
+void AllocateThreadIdentityKey(ThreadIdentityReclaimerFunction reclaimer) {
+ pthread_key_create(&thread_identity_pthread_key, reclaimer);
+ pthread_key_initialized.store(true, std::memory_order_release);
+}
+} // namespace
+#endif
+
+#if ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_TLS || \
+ ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_CPP11
+// The actual TLS storage for a thread's currently associated ThreadIdentity.
+// This is referenced by inline accessors in the header.
+// "protected" visibility ensures that if multiple copies of //base exist in a
+// process (via dlopen() or similar), references to
+// thread_identity_ptr from each copy of the code will refer to
+// *different* instances of this ptr. See extensive discussion of this choice
+// in cl/90634708
+// TODO(ahh): hard deprecate multiple copies of //base; remove this.
+#ifdef __GNUC__
+__attribute__((visibility("protected")))
+#endif // __GNUC__
+ ABSL_PER_THREAD_TLS_KEYWORD ThreadIdentity* thread_identity_ptr;
+#endif // TLS or CPP11
+
+void SetCurrentThreadIdentity(
+ ThreadIdentity* identity, ThreadIdentityReclaimerFunction reclaimer) {
+ assert(CurrentThreadIdentityIfPresent() == nullptr);
+ // Associate our destructor.
+ // NOTE: This call to pthread_setspecific is currently the only immovable
+ // barrier to CurrentThreadIdentity() always being async signal safe.
+#if ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_POSIX_SETSPECIFIC
+ // NOTE: Not async-safe. But can be open-coded.
+ absl::call_once(init_thread_identity_key_once, AllocateThreadIdentityKey,
+ reclaimer);
+ // b/18366710:
+ // We must mask signals around the call to setspecific as with current glibc,
+ // a concurrent getspecific (needed for GetCurrentThreadIdentityIfPresent())
+ // may zero our value.
+ //
+ // While not officially async-signal safe, getspecific within a signal handler
+ // is otherwise OK.
+ sigset_t all_signals;
+ sigset_t curr_signals;
+ sigfillset(&all_signals);
+ pthread_sigmask(SIG_SETMASK, &all_signals, &curr_signals);
+ pthread_setspecific(thread_identity_pthread_key,
+ reinterpret_cast<void*>(identity));
+ pthread_sigmask(SIG_SETMASK, &curr_signals, nullptr);
+#elif ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_TLS
+ // NOTE: Not async-safe. But can be open-coded.
+ absl::call_once(init_thread_identity_key_once, AllocateThreadIdentityKey,
+ reclaimer);
+ pthread_setspecific(thread_identity_pthread_key,
+ reinterpret_cast<void*>(identity));
+ thread_identity_ptr = identity;
+#elif ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_CPP11
+ thread_local std::unique_ptr<ThreadIdentity, ThreadIdentityReclaimerFunction>
+ holder(identity, reclaimer);
+ thread_identity_ptr = identity;
+#else
+#error Unimplemented ABSL_THREAD_IDENTITY_MODE
+#endif
+}
+
+void ClearCurrentThreadIdentity() {
+#if ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_TLS || \
+ ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_CPP11
+ thread_identity_ptr = nullptr;
+#elif ABSL_THREAD_IDENTITY_MODE == \
+ ABSL_THREAD_IDENTITY_MODE_USE_POSIX_SETSPECIFIC
+ // pthread_setspecific expected to clear value on destruction
+ assert(CurrentThreadIdentityIfPresent() == nullptr);
+#endif
+}
+
+#if ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_POSIX_SETSPECIFIC
+ThreadIdentity* CurrentThreadIdentityIfPresent() {
+ bool initialized = pthread_key_initialized.load(std::memory_order_acquire);
+ if (!initialized) {
+ return nullptr;
+ }
+ return reinterpret_cast<ThreadIdentity*>(
+ pthread_getspecific(thread_identity_pthread_key));
+}
+#endif
+
+} // namespace base_internal
+} // namespace absl