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// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
// vim: ts=8 sw=2 smarttab
/*
* Ceph - scalable distributed file system
*
* Copyright (C) 2011 New Dream Network
*
* This is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License version 2.1, as published by the Free Software
* Foundation. See file COPYING.
*
*/
#include "cross_process_sem.h"
#include <errno.h>
#include <semaphore.h>
#include <stdlib.h>
#include <sys/mman.h>
#include "include/ceph_assert.h"
/* We put our cross-process semaphore into a page of memory mapped with mmap. */
struct cross_process_sem_data_t
{
sem_t sem;
};
/* A factory function is a good choice here because we want to be able to
* return an error code. It does force heap allocation, but that is the
* easiest way to use synchronization primitives anyway. Most programmers don't
* care about destroying semaphores before the process finishes. It's pretty
* difficult to get it right and there is usually no benefit.
*/
int CrossProcessSem::
create(int initial_val, CrossProcessSem** res)
{
struct cross_process_sem_data_t *data = static_cast < cross_process_sem_data_t*> (
mmap(NULL, sizeof(struct cross_process_sem_data_t),
PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS, -1, 0));
if (data == MAP_FAILED) {
int err = errno;
return err;
}
int ret = sem_init(&data->sem, 1, initial_val);
if (ret) {
return ret;
}
*res = new CrossProcessSem(data);
return 0;
}
CrossProcessSem::
~CrossProcessSem()
{
munmap(m_data, sizeof(struct cross_process_sem_data_t));
m_data = NULL;
}
void CrossProcessSem::
wait()
{
while(true) {
int ret = sem_wait(&m_data->sem);
if (ret == 0)
return;
int err = errno;
if (err == -EINTR)
continue;
ceph_abort();
}
}
void CrossProcessSem::
post()
{
int ret = sem_post(&m_data->sem);
if (ret == -1) {
ceph_abort();
}
}
int CrossProcessSem::
reinit(int dval)
{
if (dval < 0)
return -EINVAL;
int cval;
if (sem_getvalue(&m_data->sem, &cval) == -1)
return errno;
if (cval < dval) {
int diff = dval - cval;
for (int i = 0; i < diff; ++i)
sem_post(&m_data->sem);
}
else {
int diff = cval - dval;
for (int i = 0; i < diff; ++i)
sem_wait(&m_data->sem);
}
return 0;
}
CrossProcessSem::
CrossProcessSem(struct cross_process_sem_data_t *data)
: m_data(data)
{
}
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