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/*
* Copyright 2018 Google
*
* 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 "Firestore/core/src/firebase/firestore/util/executor_std.h"
#include <future> // NOLINT(build/c++11)
#include <sstream>
namespace firebase {
namespace firestore {
namespace util {
namespace internal {
namespace {
// The only guarantee is that different `thread_id`s will produce different
// values.
std::string ThreadIdToString(const std::thread::id thread_id) {
std::ostringstream stream;
stream << thread_id;
return stream.str();
}
} // namespace
ExecutorStd::ExecutorStd() {
// Somewhat counter-intuitively, constructor of `std::atomic` assigns the
// value non-atomically, so the atomic initialization must be provided here,
// before the worker thread is started.
// See [this thread](https://stackoverflow.com/questions/25609858) for context
// on the constructor.
current_id_ = 0;
shutting_down_ = false;
worker_thread_ = std::thread{&ExecutorStd::PollingThread, this};
}
ExecutorStd::~ExecutorStd() {
shutting_down_ = true;
// Make sure the worker thread is not blocked, so that the call to `join`
// doesn't hang.
UnblockQueue();
worker_thread_.join();
}
void ExecutorStd::Execute(Operation&& operation) {
PushOnSchedule(std::move(operation), Immediate());
}
DelayedOperation ExecutorStd::Schedule(const Milliseconds delay,
TaggedOperation&& tagged) {
// While negative delay can be interpreted as a request for immediate
// execution, supporting it would provide a hacky way to modify FIFO ordering
// of immediate operations.
FIREBASE_ASSERT_MESSAGE(delay.count() >= 0,
"Schedule: delay cannot be negative");
namespace chr = std::chrono;
const auto now = chr::time_point_cast<Milliseconds>(chr::steady_clock::now());
const auto id =
PushOnSchedule(std::move(tagged.operation), now + delay, tagged.tag);
return DelayedOperation{[this, id] { TryCancel(id); }};
}
void ExecutorStd::TryCancel(const Id operation_id) {
schedule_.RemoveIf(
[operation_id](const Entry& e) { return e.id == operation_id; });
}
ExecutorStd::Id ExecutorStd::PushOnSchedule(Operation&& operation,
const TimePoint when,
const Tag tag) {
// Note: operations scheduled for immediate execution don't actually need an
// id. This could be tweaked to reuse the same id for all such operations.
const auto id = NextId();
schedule_.Push(Entry{std::move(operation), id, tag}, when);
return id;
}
void ExecutorStd::PollingThread() {
while (!shutting_down_) {
Entry entry = schedule_.PopBlocking();
if (entry.tagged.operation) {
entry.tagged.operation();
}
}
}
void ExecutorStd::UnblockQueue() {
// Put a no-op for immediate execution on the queue to ensure that
// `schedule_.PopBlocking` returns, and worker thread can notice that shutdown
// is in progress.
schedule_.Push(Entry{[] {}, /*id=*/0}, Immediate());
}
ExecutorStd::Id ExecutorStd::NextId() {
// The wrap around after ~4 billion operations is explicitly ignored. Even if
// an instance of `ExecutorStd` runs long enough to get `current_id_` to
// overflow, it's extremely unlikely that any object still holds a reference
// that is old enough to cause a conflict.
return current_id_++;
}
bool ExecutorStd::IsCurrentExecutor() const {
return std::this_thread::get_id() == worker_thread_.get_id();
}
std::string ExecutorStd::CurrentExecutorName() const {
return ThreadIdToString(std::this_thread::get_id());
}
std::string ExecutorStd::Name() const {
return ThreadIdToString(worker_thread_.get_id());
}
void ExecutorStd::ExecuteBlocking(Operation&& operation) {
std::promise<void> signal_finished;
Execute([&] {
operation();
signal_finished.set_value();
});
signal_finished.get_future().wait();
}
bool ExecutorStd::IsScheduled(const Tag tag) const {
return schedule_.Contains(
[&tag](const Entry& e) { return e.tagged.tag == tag; });
}
absl::optional<Executor::TaggedOperation> ExecutorStd::PopFromSchedule() {
auto removed =
schedule_.RemoveIf([](const Entry& e) { return !e.IsImmediate(); });
if (!removed.has_value()) {
return {};
}
return {std::move(removed.value().tagged)};
}
} // namespace internal
} // namespace util
} // namespace firestore
} // namespace firebase
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