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author | 2017-09-19 16:54:40 -0400 | |
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committer | 2017-09-19 16:54:40 -0400 | |
commit | c2e754829628d1e9b7a16b3389cfdace76950fdf (patch) | |
tree | 5a7f056f44e27c30e10025113b644f0b3b5801fc /absl/synchronization/internal/per_thread_sem.h |
Initial Commit
Diffstat (limited to 'absl/synchronization/internal/per_thread_sem.h')
-rw-r--r-- | absl/synchronization/internal/per_thread_sem.h | 107 |
1 files changed, 107 insertions, 0 deletions
diff --git a/absl/synchronization/internal/per_thread_sem.h b/absl/synchronization/internal/per_thread_sem.h new file mode 100644 index 00000000..678b69e4 --- /dev/null +++ b/absl/synchronization/internal/per_thread_sem.h @@ -0,0 +1,107 @@ +// 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. +// + +// 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_ |