| // 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. |
| |
| #ifndef ABSL_SYNCHRONIZATION_INTERNAL_PER_THREAD_SEM_H_ |
| #define ABSL_SYNCHRONIZATION_INTERNAL_PER_THREAD_SEM_H_ |
| |
| #include <atomic> |
| |
| #include "absl/base/internal/thread_identity.h" |
| #include "absl/synchronization/internal/create_thread_identity.h" |
| #include "absl/synchronization/internal/kernel_timeout.h" |
| |
| namespace absl { |
| |
| 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 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); |
| |
| // White-listed callers. |
| friend class PerThreadSemTest; |
| friend class absl::Mutex; |
| friend absl::base_internal::ThreadIdentity* CreateThreadIdentity(); |
| }; |
| |
| } // namespace synchronization_internal |
| } // 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 AbslInternalPerThreadSemPost( |
| absl::base_internal::ThreadIdentity* identity); |
| bool AbslInternalPerThreadSemWait( |
| absl::synchronization_internal::KernelTimeout t); |
| } // extern "C" |
| |
| void absl::synchronization_internal::PerThreadSem::Post( |
| absl::base_internal::ThreadIdentity* identity) { |
| AbslInternalPerThreadSemPost(identity); |
| } |
| |
| bool absl::synchronization_internal::PerThreadSem::Wait( |
| absl::synchronization_internal::KernelTimeout t) { |
| return AbslInternalPerThreadSemWait(t); |
| } |
| |
| #endif // ABSL_SYNCHRONIZATION_INTERNAL_PER_THREAD_SEM_H_ |