| // 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. | |
| // Operations to make atomic transitions on a word, and to allow | |
| // waiting for those transitions to become possible. | |
| namespace absl { | |
| ABSL_NAMESPACE_BEGIN | |
| namespace base_internal { | |
| // SpinLockWait() waits until it can perform one of several transitions from | |
| // "from" to "to". It returns when it performs a transition where done==true. | |
| struct SpinLockWaitTransition { | |
| uint32_t from; | |
| uint32_t to; | |
| bool done; | |
| }; | |
| // Wait until *w can transition from trans[i].from to trans[i].to for some i | |
| // satisfying 0<=i<n && trans[i].done, atomically make the transition, | |
| // then return the old value of *w. Make any other atomic transitions | |
| // where !trans[i].done, but continue waiting. | |
| // | |
| // Wakeups for threads blocked on SpinLockWait do not respect priorities. | |
| uint32_t SpinLockWait(std::atomic<uint32_t> *w, int n, | |
| const SpinLockWaitTransition trans[], | |
| SchedulingMode scheduling_mode); | |
| // If possible, wake some thread that has called SpinLockDelay(w, ...). If `all` | |
| // is true, wake all such threads. On some systems, this may be a no-op; on | |
| // those systems, threads calling SpinLockDelay() will always wake eventually | |
| // even if SpinLockWake() is never called. | |
| void SpinLockWake(std::atomic<uint32_t> *w, bool all); | |
| // Wait for an appropriate spin delay on iteration "loop" of a | |
| // spin loop on location *w, whose previously observed value was "value". | |
| // SpinLockDelay() may do nothing, may yield the CPU, may sleep a clock tick, | |
| // or may wait for a call to SpinLockWake(w). | |
| void SpinLockDelay(std::atomic<uint32_t> *w, uint32_t value, int loop, | |
| base_internal::SchedulingMode scheduling_mode); | |
| // Helper used by AbslInternalSpinLockDelay. | |
| // Returns a suggested delay in nanoseconds for iteration number "loop". | |
| int SpinLockSuggestedDelayNS(int loop); | |
| } // namespace base_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(AbslInternalSpinLockWake)(std::atomic<uint32_t> *w, | |
| bool all); | |
| void ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockDelay)( | |
| std::atomic<uint32_t> *w, uint32_t value, int loop, | |
| absl::base_internal::SchedulingMode scheduling_mode); | |
| } | |
| inline void absl::base_internal::SpinLockWake(std::atomic<uint32_t> *w, | |
| bool all) { | |
| ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockWake)(w, all); | |
| } | |
| inline void absl::base_internal::SpinLockDelay( | |
| std::atomic<uint32_t> *w, uint32_t value, int loop, | |
| absl::base_internal::SchedulingMode scheduling_mode) { | |
| ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockDelay) | |
| (w, value, loop, scheduling_mode); | |
| } | |