/************************************************************
* mm_sem.c
*
* Copyright (C) 2007 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <spudmonkey@racsa.co.cr>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
* 3. Neither the name Gregory Nutt nor the names of its contributors may be
* used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
************************************************************/
/************************************************************
* Included Files
************************************************************/
#include "mm_environment.h"
#include <unistd.h>
#include <semaphore.h>
#include <errno.h>
#include <assert.h>
#include "mm_internal.h"
/************************************************************
* Definitions
************************************************************/
/* Define the following to enable semaphore state monitoring */
//#define MONITOR_MM_SEMAPHORE 1
#ifdef MONITOR_MM_SEMAPHORE
# ifdef CONFIG_DEBUG
# include <debug.h>
# define msemdbg dbg
# else
# define msemdbg printf
# endif
#else
# define msemdbg(x...)
#endif
/************************************************************
* Private Data
************************************************************/
/* Mutually exclusive access to this data set is enforced with
* the following (un-named) semaphore. */
static sem_t g_mm_semaphore;
static pid_t g_holder;
static int g_counts_held;
/************************************************************
* Public Functions
************************************************************/
/************************************************************
* mm_seminitialize
************************************************************/
void mm_seminitialize(void)
{
/* Initialize the MM semaphore to one (to support one-at-
* a-time access to private data sets.
*/
(void)sem_init(&g_mm_semaphore, 0, 1);
g_holder = -1;
g_counts_held = 0;
}
/************************************************************
* mm_takesemaphore
************************************************************/
void mm_takesemaphore(void)
{
pid_t my_pid = getpid();
/* Do I already have the semaphore? */
if (g_holder == my_pid)
{
/* Yes, just increment the number of references that I have */
g_counts_held++;
}
else
{
/* Take the semaphore (perhaps waiting) */
msemdbg("%s: PID=%d taking\n", __FUNCTION__, my_pid);
while (sem_wait(&g_mm_semaphore) != 0)
{
/* The only case that an error should occur here is if
* the wait was awakened by a signal.
*/
ASSERT(mm_errno == EINTR);
}
/* We have it. Claim the stak and return */
g_holder = my_pid;
g_counts_held = 1;
}
msemdbg("%s: Holder=%d count=%d\n",
__FUNCTION__, g_holder, g_counts_held);
}
/************************************************************
* mm_givesemaphore
************************************************************/
void mm_givesemaphore(void)
{
pid_t my_pid = getpid();
/* I better be holding at least one reference to the semaphore */
ASSERT(g_holder == my_pid);
/* Do I hold multiple references to the semphore */
if (g_counts_held > 1)
{
/* Yes, just release one count and return */
g_counts_held--;
msemdbg("%s: Holder=%d count=%d\n",
__FUNCTION__, g_holder, g_counts_held);
}
else
{
/* Nope, this is the last reference I have */
msemdbg("%s: PID=%d giving\n", __FUNCTION__, my_pid);
g_holder = -1;
g_counts_held = 0;
ASSERT(sem_post(&g_mm_semaphore) == 0);
}
}
#ifdef MM_TEST
int mm_getsemaphore(void)
{
int sval;
sem_getvalue(&g_mm_semaphore, &sval);
return sval;
}
#endif
