113 lines
3.2 KiB
C++
113 lines
3.2 KiB
C++
/*
|
|
* Copyright (c) Facebook, Inc. and its 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 <folly/futures/Barrier.h>
|
|
#include <folly/lang/Exception.h>
|
|
|
|
#include <glog/logging.h>
|
|
|
|
namespace folly {
|
|
namespace futures {
|
|
|
|
Barrier::Barrier(uint32_t n)
|
|
: size_(n), controlBlock_(allocateControlBlock()) {}
|
|
|
|
Barrier::~Barrier() {
|
|
auto block = controlBlock_.load(std::memory_order_relaxed);
|
|
auto prev = block->valueAndReaderCount.load(std::memory_order_relaxed);
|
|
DCHECK_EQ(prev >> kReaderShift, 0u);
|
|
auto val = prev & kValueMask;
|
|
auto p = promises(block);
|
|
|
|
for (uint32_t i = 0; i < val; ++i) {
|
|
p[i].setException(
|
|
folly::make_exception_wrapper<std::runtime_error>("Barrier destroyed"));
|
|
}
|
|
|
|
freeControlBlock(controlBlock_);
|
|
}
|
|
|
|
auto Barrier::allocateControlBlock() -> ControlBlock* {
|
|
auto storage = malloc(controlBlockSize(size_));
|
|
if (!storage) {
|
|
throw_exception<std::bad_alloc>();
|
|
}
|
|
auto block = ::new (storage) ControlBlock();
|
|
|
|
auto p = promises(block);
|
|
uint32_t i = 0;
|
|
try {
|
|
for (i = 0; i < size_; ++i) {
|
|
new (p + i) BoolPromise();
|
|
}
|
|
} catch (...) {
|
|
for (; i != 0; --i) {
|
|
p[i - 1].~BoolPromise();
|
|
}
|
|
throw;
|
|
}
|
|
|
|
return block;
|
|
}
|
|
|
|
void Barrier::freeControlBlock(ControlBlock* block) {
|
|
auto p = promises(block);
|
|
for (uint32_t i = size_; i != 0; --i) {
|
|
p[i - 1].~BoolPromise();
|
|
}
|
|
free(block);
|
|
}
|
|
|
|
folly::Future<bool> Barrier::wait() {
|
|
// Load the current control block first. As we know there is at least
|
|
// one thread in the current epoch (us), this means that the value is
|
|
// < size_, so controlBlock_ can't change until we bump the value below.
|
|
auto block = controlBlock_.load(std::memory_order_acquire);
|
|
auto p = promises(block);
|
|
|
|
// Bump the value and record ourselves as reader.
|
|
// This ensures that block stays allocated, as the reader count is > 0.
|
|
auto prev = block->valueAndReaderCount.fetch_add(
|
|
kReader + 1, std::memory_order_acquire);
|
|
|
|
auto prevValue = static_cast<uint32_t>(prev & kValueMask);
|
|
DCHECK_LT(prevValue, size_);
|
|
auto future = p[prevValue].getFuture();
|
|
|
|
if (prevValue + 1 == size_) {
|
|
// Need to reset the barrier before fulfilling any futures. This is
|
|
// when the epoch is flipped to the next.
|
|
controlBlock_.store(allocateControlBlock(), std::memory_order_release);
|
|
|
|
p[0].setValue(true);
|
|
for (uint32_t i = 1; i < size_; ++i) {
|
|
p[i].setValue(false);
|
|
}
|
|
}
|
|
|
|
// Free the control block if we're the last reader at max value.
|
|
prev =
|
|
block->valueAndReaderCount.fetch_sub(kReader, std::memory_order_acq_rel);
|
|
if (prev == (kReader | uint64_t(size_))) {
|
|
freeControlBlock(block);
|
|
}
|
|
|
|
return future;
|
|
}
|
|
|
|
} // namespace futures
|
|
} // namespace folly
|