src/bthread/butex.h

// 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.

// bthread - An M:N threading library to make applications more concurrent.

// Date: Tue Jul 22 17:30:12 CST 2014

#ifndef BTHREAD_BUTEX_H
#define BTHREAD_BUTEX_H

#include <errno.h>                               // users need to check errno
#include <time.h>                                // timespec
#include "butil/macros.h"                         // BAIDU_CASSERT
#include "bthread/types.h"                       // bthread_t

namespace bthread {

// If a thread would suspend for less than so many microseconds, return
// ETIMEDOUT directly.
// Use 1: sleeping for less than 2 microsecond is inefficient and useless.
static const int64_t MIN_SLEEP_US = 2;

// Create a butex which is a futex-like 32-bit primitive for synchronizing
// bthreads/pthreads.
// Returns a pointer to 32-bit data, NULL on failure.
// NOTE: all butexes are private(not inter-process).
void* butex_create();

// Check width of user type before casting.
template <typename T> T* butex_create_checked() {
    BAIDU_CASSERT(sizeof(T) == sizeof(int), sizeof_T_must_equal_int);
    return static_cast<T*>(butex_create());
}

// Destroy the butex.
void butex_destroy(void* butex);

// Wake up at most 1 thread waiting on |butex|.
// Returns # of threads woken up.
int butex_wake(void* butex, bool nosignal = false);

// Wake up all threads waiting on |butex| if n is zero,
// Otherwise, wake up at most n thread waiting on |butex|.
// Returns # of threads woken up.
int butex_wake_n(void* butex, size_t n, bool nosignal = false);

// Wake up all threads waiting on |butex|.
// Returns # of threads woken up.
int butex_wake_all(void* butex, bool nosignal = false);

// Wake up all threads waiting on |butex| except a bthread whose identifier
// is |excluded_bthread|. This function does not yield.
// Returns # of threads woken up.
int butex_wake_except(void* butex, bthread_t excluded_bthread);

// Wake up at most 1 thread waiting on |butex1|, let all other threads wait
// on |butex2| instead.
// Returns # of threads woken up.
int butex_requeue(void* butex1, void* butex2);

// Atomically wait on |butex| if *butex equals |expected_value|, until the
// butex is woken up by butex_wake*, or CLOCK_REALTIME reached |abstime| if
// abstime is not NULL.
// About |abstime|:
//   Different from FUTEX_WAIT, butex_wait uses absolute time.
// About |prepend|:
//   If |prepend| is true, queue the bthread at the head of the queue,
//   otherwise at the tail.
// Returns 0 on success, -1 otherwise and errno is set.
int butex_wait(void* butex, int expected_value,
               const timespec* abstime,
               bool prepend = false);

}  // namespace bthread

#endif  // BTHREAD_BUTEX_H