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#pragma clang system_header
// 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.
#pragma once
#include <memory>
#include "arrow/util/macros.h"
#include "arrow/util/visibility.h"
namespace arrow20 {
namespace util {
/// A wrapper around std::mutex since we can't use it directly in
/// public headers due to C++/CLI.
/// https://docs.microsoft.com/en-us/cpp/standard-library/mutex#remarks
class ARROW_EXPORT Mutex {
public:
Mutex();
Mutex(Mutex&&) = default;
Mutex& operator=(Mutex&&) = default;
/// A Guard is falsy if a lock could not be acquired.
class ARROW_EXPORT Guard {
public:
Guard() : locked_(NULLPTR, [](Mutex* mutex) {}) {}
Guard(Guard&&) = default;
Guard& operator=(Guard&&) = default;
explicit operator bool() const { return bool(locked_); }
void Unlock() { locked_.reset(); }
private:
explicit Guard(Mutex* locked);
std::unique_ptr<Mutex, void (*)(Mutex*)> locked_;
friend Mutex;
};
Guard TryLock();
Guard Lock();
private:
struct Impl;
std::unique_ptr<Impl, void (*)(Impl*)> impl_;
};
#ifndef _WIN32
/// Return a pointer to a process-wide, process-specific Mutex that can be used
/// at any point in a child process. NULL is returned when called in the parent.
///
/// The rule is to first check that getpid() corresponds to the parent process pid
/// and, if not, call this function to lock any after-fork reinitialization code.
/// Like this:
///
/// std::atomic<pid_t> pid{getpid()};
/// ...
/// if (pid.load() != getpid()) {
/// // In child process
/// auto lock = GlobalForkSafeMutex()->Lock();
/// if (pid.load() != getpid()) {
/// // Reinitialize internal structures after fork
/// ...
/// pid.store(getpid());
ARROW_EXPORT
Mutex* GlobalForkSafeMutex();
#endif
} // namespace util
} // namespace arrow20
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