thread_identity.cc
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1 // Copyright 2017 The Abseil Authors.
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 // https://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14 
16 
17 #ifndef _WIN32
18 #include <pthread.h>
19 #include <signal.h>
20 #endif
21 
22 #include <atomic>
23 #include <cassert>
24 #include <memory>
25 
26 #include "absl/base/call_once.h"
29 
30 namespace absl {
31 namespace base_internal {
32 
33 #if ABSL_THREAD_IDENTITY_MODE != ABSL_THREAD_IDENTITY_MODE_USE_CPP11
34 namespace {
35 // Used to co-ordinate one-time creation of our pthread_key
36 absl::once_flag init_thread_identity_key_once;
37 pthread_key_t thread_identity_pthread_key;
38 std::atomic<bool> pthread_key_initialized(false);
39 
40 void AllocateThreadIdentityKey(ThreadIdentityReclaimerFunction reclaimer) {
41  pthread_key_create(&thread_identity_pthread_key, reclaimer);
42  pthread_key_initialized.store(true, std::memory_order_release);
43 }
44 } // namespace
45 #endif
46 
47 #if ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_TLS || \
48  ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_CPP11
49 // The actual TLS storage for a thread's currently associated ThreadIdentity.
50 // This is referenced by inline accessors in the header.
51 // "protected" visibility ensures that if multiple instances of Abseil code
52 // exist within a process (via dlopen() or similar), references to
53 // thread_identity_ptr from each instance of the code will refer to
54 // *different* instances of this ptr.
55 #ifdef __GNUC__
56 __attribute__((visibility("protected")))
57 #endif // __GNUC__
59 #endif // TLS or CPP11
60 
62  ThreadIdentity* identity, ThreadIdentityReclaimerFunction reclaimer) {
63  assert(CurrentThreadIdentityIfPresent() == nullptr);
64  // Associate our destructor.
65  // NOTE: This call to pthread_setspecific is currently the only immovable
66  // barrier to CurrentThreadIdentity() always being async signal safe.
67 #if ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_POSIX_SETSPECIFIC
68  // NOTE: Not async-safe. But can be open-coded.
69  absl::call_once(init_thread_identity_key_once, AllocateThreadIdentityKey,
70  reclaimer);
71 
72 #ifdef __EMSCRIPTEN__
73  // Emscripten PThread implementation does not support signals.
74  // See https://kripken.github.io/emscripten-site/docs/porting/pthreads.html
75  // for more information.
76  pthread_setspecific(thread_identity_pthread_key,
77  reinterpret_cast<void*>(identity));
78 #else
79  // We must mask signals around the call to setspecific as with current glibc,
80  // a concurrent getspecific (needed for GetCurrentThreadIdentityIfPresent())
81  // may zero our value.
82  //
83  // While not officially async-signal safe, getspecific within a signal handler
84  // is otherwise OK.
85  sigset_t all_signals;
86  sigset_t curr_signals;
87  sigfillset(&all_signals);
88  pthread_sigmask(SIG_SETMASK, &all_signals, &curr_signals);
89  pthread_setspecific(thread_identity_pthread_key,
90  reinterpret_cast<void*>(identity));
91  pthread_sigmask(SIG_SETMASK, &curr_signals, nullptr);
92 #endif // !__EMSCRIPTEN__
93 
94 #elif ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_TLS
95  // NOTE: Not async-safe. But can be open-coded.
96  absl::call_once(init_thread_identity_key_once, AllocateThreadIdentityKey,
97  reclaimer);
98  pthread_setspecific(thread_identity_pthread_key,
99  reinterpret_cast<void*>(identity));
100  thread_identity_ptr = identity;
101 #elif ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_CPP11
102  thread_local std::unique_ptr<ThreadIdentity, ThreadIdentityReclaimerFunction>
103  holder(identity, reclaimer);
104  thread_identity_ptr = identity;
105 #else
106 #error Unimplemented ABSL_THREAD_IDENTITY_MODE
107 #endif
108 }
109 
111 #if ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_TLS || \
112  ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_CPP11
113  thread_identity_ptr = nullptr;
114 #elif ABSL_THREAD_IDENTITY_MODE == \
115  ABSL_THREAD_IDENTITY_MODE_USE_POSIX_SETSPECIFIC
116  // pthread_setspecific expected to clear value on destruction
117  assert(CurrentThreadIdentityIfPresent() == nullptr);
118 #endif
119 }
120 
121 #if ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_POSIX_SETSPECIFIC
123  bool initialized = pthread_key_initialized.load(std::memory_order_acquire);
124  if (!initialized) {
125  return nullptr;
126  }
127  return reinterpret_cast<ThreadIdentity*>(
128  pthread_getspecific(thread_identity_pthread_key));
129 }
130 #endif
131 
132 } // namespace base_internal
133 } // namespace absl
ABSL_PER_THREAD_TLS_KEYWORD ThreadIdentity * thread_identity_ptr
void(*)(void *) ThreadIdentityReclaimerFunction
ThreadIdentity * CurrentThreadIdentityIfPresent()
Definition: algorithm.h:29
void call_once(absl::once_flag &flag, Callable &&fn, Args &&... args)
Definition: call_once.h:202
void SetCurrentThreadIdentity(ThreadIdentity *identity, ThreadIdentityReclaimerFunction reclaimer)
#define ABSL_PER_THREAD_TLS_KEYWORD


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autogenerated on Mon Feb 28 2022 21:31:20