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// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements. See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership. The ASF licenses this file
// to you 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 "contrib/libs/apache/arrow_next/cpp/src/arrow/util/atfork_internal.h"
#include <algorithm>
#include <atomic>
#include <mutex>
#include <vector>
#ifndef _WIN32
# include <pthread.h>
#endif
#include "contrib/libs/apache/arrow_next/cpp/src/arrow/util/io_util.h"
#include "contrib/libs/apache/arrow_next/cpp/src/arrow/util/logging.h"
namespace arrow20 {
namespace internal {
namespace {
// Singleton state for at-fork management.
// We do not use global variables because of initialization order issues (ARROW-18383).
// Instead, a function-local static ensures the state is initialized
// opportunistically (see GetAtForkState()).
struct AtForkState {
struct RunningHandler {
// A temporary owning copy of a handler, to make sure that a handler
// that runs before fork can still run after fork.
std::shared_ptr<AtForkHandler> handler;
// The token returned by the before-fork handler, to pass to after-fork handlers.
std::any token;
explicit RunningHandler(std::shared_ptr<AtForkHandler> handler)
: handler(std::move(handler)) {}
};
void MaintainHandlersUnlocked() {
auto it = std::remove_if(
handlers_.begin(), handlers_.end(),
[](const std::weak_ptr<AtForkHandler>& ptr) { return ptr.expired(); });
handlers_.erase(it, handlers_.end());
}
void BeforeFork() {
// Lock the mutex and keep it locked until the end of AfterForkParent(),
// to avoid multiple concurrent forks and atforks.
mutex_.lock();
DCHECK(handlers_while_forking_.empty()); // AfterForkParent clears it
for (const auto& weak_handler : handlers_) {
if (auto handler = weak_handler.lock()) {
handlers_while_forking_.emplace_back(std::move(handler));
}
}
// XXX can the handler call RegisterAtFork()?
for (auto&& handler : handlers_while_forking_) {
if (handler.handler->before) {
handler.token = handler.handler->before();
}
}
}
void AfterForkParent() {
// The mutex was locked by BeforeFork()
auto handlers = std::move(handlers_while_forking_);
handlers_while_forking_.clear();
// Execute handlers in reverse order
for (auto it = handlers.rbegin(); it != handlers.rend(); ++it) {
auto&& handler = *it;
if (handler.handler->parent_after) {
handler.handler->parent_after(std::move(handler.token));
}
}
mutex_.unlock();
// handlers will be destroyed here without the mutex locked, so that
// any action taken by destructors might call RegisterAtFork
}
void AfterForkChild() {
// Need to reinitialize the mutex as it is probably invalid. Also, the
// old mutex destructor may fail.
// Fortunately, we are a single thread in the child process by now, so no
// additional synchronization is needed.
new (&mutex_) std::mutex;
auto handlers = std::move(handlers_while_forking_);
handlers_while_forking_.clear();
// Execute handlers in reverse order
for (auto it = handlers.rbegin(); it != handlers.rend(); ++it) {
auto&& handler = *it;
if (handler.handler->child_after) {
handler.handler->child_after(std::move(handler.token));
}
}
}
void RegisterAtFork(std::weak_ptr<AtForkHandler> weak_handler) {
std::lock_guard<std::mutex> lock(mutex_);
// This is O(n) for each at-fork registration. We assume that n remains
// typically low and calls to this function are not performance-critical.
MaintainHandlersUnlocked();
handlers_.push_back(std::move(weak_handler));
}
std::mutex mutex_;
std::vector<std::weak_ptr<AtForkHandler>> handlers_;
std::vector<RunningHandler> handlers_while_forking_;
};
AtForkState* GetAtForkState() {
static std::unique_ptr<AtForkState> state = []() {
auto state = std::make_unique<AtForkState>();
#ifndef _WIN32
int r = pthread_atfork(/*prepare=*/[] { GetAtForkState()->BeforeFork(); },
/*parent=*/[] { GetAtForkState()->AfterForkParent(); },
/*child=*/[] { GetAtForkState()->AfterForkChild(); });
if (r != 0) {
IOErrorFromErrno(r, "Error when calling pthread_atfork: ").Abort();
}
#endif
return state;
}();
return state.get();
}
}; // namespace
void RegisterAtFork(std::weak_ptr<AtForkHandler> weak_handler) {
GetAtForkState()->RegisterAtFork(std::move(weak_handler));
}
} // namespace internal
} // namespace arrow20
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