https://github.com/facebook/folly
SharedMutex.cpp
/*
* Copyright (c) Meta Platforms, Inc. and affiliates.
*
* 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.
*/
#include <system_error>
#include <folly/SharedMutex.h>
#include <folly/Indestructible.h>
#include <folly/lang/Exception.h>
#include <folly/portability/SysResource.h>
namespace folly {
// Explicitly instantiate SharedMutex here:
template class SharedMutexImpl<true>;
template class SharedMutexImpl<false>;
namespace shared_mutex_detail {
std::unique_lock<std::mutex> annotationGuard(void* ptr) {
if (folly::kIsSanitizeThread) {
// On TSAN builds, we have an array of mutexes and index into them based on
// the address. If the array is of prime size things will work out okay
// without a complicated hash function.
static constexpr std::size_t kNumAnnotationMutexes = 251;
static Indestructible<std::array<std::mutex, kNumAnnotationMutexes>>
kAnnotationMutexes;
auto index = reinterpret_cast<uintptr_t>(ptr) % kNumAnnotationMutexes;
return std::unique_lock<std::mutex>((*kAnnotationMutexes)[index]);
} else {
return std::unique_lock<std::mutex>();
}
}
uint32_t getMaxDeferredReadersSlow(relaxed_atomic<uint32_t>& cache) {
uint32_t maxDeferredReaders = std::min(
static_cast<uint32_t>(
folly::nextPowTwo(CacheLocality::system().numCpus) << 1),
shared_mutex_detail::kMaxDeferredReadersAllocated);
// maxDeferredReaders must be a power of 2
assert(!(maxDeferredReaders & (maxDeferredReaders - 1)));
cache = maxDeferredReaders;
return maxDeferredReaders;
}
long getCurrentThreadInvoluntaryContextSwitchCount() {
#ifdef RUSAGE_THREAD
struct rusage usage;
if (getrusage(RUSAGE_THREAD, &usage)) {
return 0;
} else {
return usage.ru_nivcsw;
}
#else
return 0;
#endif
}
[[noreturn]] void throwOperationNotPermitted() {
folly::throw_exception<std::system_error>(
std::make_error_code(std::errc::operation_not_permitted));
}
[[noreturn]] void throwDeadlockWouldOccur() {
folly::throw_exception<std::system_error>(
std::make_error_code(std::errc::resource_deadlock_would_occur));
}
} // namespace shared_mutex_detail
} // namespace folly