| // 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 | |
| // | |
| // 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. | |
| // | |
| // PerThreadSem is a low-level synchronization primitive controlling the | |
| // runnability of a single thread, used internally by Mutex and CondVar. | |
| // | |
| // This is NOT a general-purpose synchronization mechanism, and should not be | |
| // used directly by applications. Applications should use Mutex and CondVar. | |
| // | |
| // The semantics of PerThreadSem are the same as that of a counting semaphore. | |
| // Each thread maintains an abstract "count" value associated with its identity. | |
| namespace absl { | |
| ABSL_NAMESPACE_BEGIN | |
| class Mutex; | |
| namespace synchronization_internal { | |
| class PerThreadSem { | |
| public: | |
| PerThreadSem() = delete; | |
| PerThreadSem(const PerThreadSem&) = delete; | |
| PerThreadSem& operator=(const PerThreadSem&) = delete; | |
| // Routine invoked periodically (once a second) by a background thread. | |
| // Has no effect on user-visible state. | |
| static void Tick(base_internal::ThreadIdentity* identity); | |
| // --------------------------------------------------------------------------- | |
| // Routines used by autosizing threadpools to detect when threads are | |
| // blocked. Each thread has a counter pointer, initially zero. If non-zero, | |
| // the implementation atomically increments the counter when it blocks on a | |
| // semaphore, a decrements it again when it wakes. This allows a threadpool | |
| // to keep track of how many of its threads are blocked. | |
| // SetThreadBlockedCounter() should be used only by threadpool | |
| // implementations. GetThreadBlockedCounter() should be used by modules that | |
| // block threads; if the pointer returned is non-zero, the location should be | |
| // incremented before the thread blocks, and decremented after it wakes. | |
| static void SetThreadBlockedCounter(std::atomic<int> *counter); | |
| static std::atomic<int> *GetThreadBlockedCounter(); | |
| private: | |
| // Create the PerThreadSem associated with "identity". Initializes count=0. | |
| // REQUIRES: May only be called by ThreadIdentity. | |
| static inline void Init(base_internal::ThreadIdentity* identity); | |
| // Increments "identity"'s count. | |
| static inline void Post(base_internal::ThreadIdentity* identity); | |
| // Waits until either our count > 0 or t has expired. | |
| // If count > 0, decrements count and returns true. Otherwise returns false. | |
| // !t.has_timeout() => Wait(t) will return true. | |
| static inline bool Wait(KernelTimeout t); | |
| // Permitted callers. | |
| friend class PerThreadSemTest; | |
| friend class absl::Mutex; | |
| friend void OneTimeInitThreadIdentity(absl::base_internal::ThreadIdentity*); | |
| }; | |
| } // namespace synchronization_internal | |
| ABSL_NAMESPACE_END | |
| } // namespace absl | |
| // In some build configurations we pass --detect-odr-violations to the | |
| // gold linker. This causes it to flag weak symbol overrides as ODR | |
| // violations. Because ODR only applies to C++ and not C, | |
| // --detect-odr-violations ignores symbols not mangled with C++ names. | |
| // By changing our extension points to be extern "C", we dodge this | |
| // check. | |
| extern "C" { | |
| void ABSL_INTERNAL_C_SYMBOL(AbslInternalPerThreadSemInit)( | |
| absl::base_internal::ThreadIdentity* identity); | |
| void ABSL_INTERNAL_C_SYMBOL(AbslInternalPerThreadSemPost)( | |
| absl::base_internal::ThreadIdentity* identity); | |
| bool ABSL_INTERNAL_C_SYMBOL(AbslInternalPerThreadSemWait)( | |
| absl::synchronization_internal::KernelTimeout t); | |
| void ABSL_INTERNAL_C_SYMBOL(AbslInternalPerThreadSemPoke)( | |
| absl::base_internal::ThreadIdentity* identity); | |
| } // extern "C" | |
| void absl::synchronization_internal::PerThreadSem::Init( | |
| absl::base_internal::ThreadIdentity* identity) { | |
| ABSL_INTERNAL_C_SYMBOL(AbslInternalPerThreadSemInit)(identity); | |
| } | |
| void absl::synchronization_internal::PerThreadSem::Post( | |
| absl::base_internal::ThreadIdentity* identity) { | |
| ABSL_INTERNAL_C_SYMBOL(AbslInternalPerThreadSemPost)(identity); | |
| } | |
| bool absl::synchronization_internal::PerThreadSem::Wait( | |
| absl::synchronization_internal::KernelTimeout t) { | |
| return ABSL_INTERNAL_C_SYMBOL(AbslInternalPerThreadSemWait)(t); | |
| } | |