1 /*

     2     SDL - Simple DirectMedia Layer

     3     Copyright (C) 1997-2006 Sam Lantinga

     4 

     5     This library is free software; you can redistribute it and/or

     6     modify it under the terms of the GNU Lesser General Public

     7     License as published by the Free Software Foundation; either

     8     version 2.1 of the License, or (at your option) any later version.

     9 

    10     This library is distributed in the hope that it will be useful,

    11     but WITHOUT ANY WARRANTY; without even the implied warranty of

    12     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

    13     Lesser General Public License for more details.

    14 

    15     You should have received a copy of the GNU Lesser General Public

    16     License along with this library; if not, write to the Free Software

    17     Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

    18 

    19     Sam Lantinga

    20     slouken@libsdl.org

    21 */

    22 #include "SDL_config.h"

    23 

    24 #include "SDL_thread.h"

    25 #include "SDL_timer.h"

    26 

    27 

    28 #include <stdio.h>

    29 #include <stdlib.h>

    30 #include <sys/types.h>

    31 #include <sys/ipc.h>

    32 #include <sys/sem.h>

    33 #include <errno.h>

    34 

    35 #include "SDL_error.h"

    36 #include "SDL_thread.h"

    37 

    38 

    39 struct SDL_semaphore {

    40 	int id;

    41 };

    42 

    43 /* Not defined by many operating systems, use configure to detect */

    44 /*

    45 #if !defined(HAVE_SEMUN)

    46 union semun {

    47 	int val;

    48 	struct semid_ds *buf;

    49 	ushort *array;

    50 };

    51 #endif

    52 */

    53 

    54 static struct sembuf op_trywait[2] = {

    55 	{ 0, -1, (IPC_NOWAIT|SEM_UNDO) } /* Decrement semaphore, no block */

    56 };

    57 static struct sembuf op_wait[2] = {

    58 	{ 0, -1, SEM_UNDO }		/* Decrement semaphore */

    59 };

    60 static struct sembuf op_post[1] = {

    61 	{ 0, 1, (IPC_NOWAIT|SEM_UNDO) }	/* Increment semaphore */

    62 };

    63 

    64 /* Create a blockable semaphore */

    65 SDL_sem *SDL_CreateSemaphore(Uint32 initial_value)

    66 {

    67 	extern int _creating_thread_lock;	/* SDL_threads.c */

    68 	SDL_sem *sem;

    69 	union semun init;

    70 

    71 	sem = (SDL_sem *)SDL_malloc(sizeof(*sem));

    72 	if ( sem == NULL ) {

    73 		SDL_OutOfMemory();

    74 		return(NULL);

    75 	}

    76 	sem->id = semget(IPC_PRIVATE, 1, (0600|IPC_CREAT));

    77 	if ( sem->id < 0 ) {

    78 		SDL_SetError("Couldn't create semaphore");

    79 		SDL_free(sem);

    80 		return(NULL);

    81 	}

    82 	init.val = initial_value;	/* Initialize semaphore */

    83 	semctl(sem->id, 0, SETVAL, init);

    84 	return(sem);

    85 }

    86 

    87 void SDL_DestroySemaphore(SDL_sem *sem)

    88 {

    89 	if ( sem ) {

    90 #ifdef __IRIX__

    91 		semctl(sem->id, 0, IPC_RMID);

    92 #else

    93 		union semun dummy;

    94 		dummy.val = 0;

    95 		semctl(sem->id, 0, IPC_RMID, dummy);

    96 #endif

    97 		SDL_free(sem);

    98 	}

    99 }

   100 

   101 int SDL_SemTryWait(SDL_sem *sem)

   102 {

   103 	int retval;

   104 

   105 	if ( ! sem ) {

   106 		SDL_SetError("Passed a NULL semaphore");

   107 		return -1;

   108 	}

   109 

   110 	retval = 0;

   111   tryagain:

   112 	if ( semop(sem->id, op_trywait, 1) < 0 ) {

   113 		if ( errno == EINTR ) {

   114 			goto tryagain;

   115 		}

   116 		retval = SDL_MUTEX_TIMEDOUT;

   117 	}

   118 	return retval;

   119 }

   120 

   121 int SDL_SemWait(SDL_sem *sem)

   122 {

   123 	int retval;

   124 

   125 	if ( ! sem ) {

   126 		SDL_SetError("Passed a NULL semaphore");

   127 		return -1;

   128 	}

   129 

   130 	retval = 0;

   131   tryagain:

   132 	if ( semop(sem->id, op_wait, 1) < 0 ) {

   133 		if ( errno == EINTR ) {

   134 			goto tryagain;

   135 		}

   136 		SDL_SetError("Semaphore operation error");

   137 		retval = -1;

   138 	}

   139 	return retval;

   140 }

   141 

   142 int SDL_SemWaitTimeout(SDL_sem *sem, Uint32 timeout)

   143 {

   144 	int retval;

   145 

   146 	if ( ! sem ) {

   147 		SDL_SetError("Passed a NULL semaphore");

   148 		return -1;

   149 	}

   150 

   151 	/* Try the easy cases first */

   152 	if ( timeout == 0 ) {

   153 		return SDL_SemTryWait(sem);

   154 	}

   155 	if ( timeout == SDL_MUTEX_MAXWAIT ) {

   156 		return SDL_SemWait(sem);

   157 	}

   158 

   159 	/* Ack!  We have to busy wait... */

   160 	timeout += SDL_GetTicks();

   161 	do {

   162 		retval = SDL_SemTryWait(sem);

   163 		if ( retval == 0 ) {

   164 			break;

   165 		}

   166 		SDL_Delay(1);

   167 	} while ( SDL_GetTicks() < timeout );

   168 

   169 	return retval;

   170 }

   171 

   172 Uint32 SDL_SemValue(SDL_sem *sem)

   173 {

   174 	int semval;

   175 	Uint32 value;

   176 	

   177 	value = 0;

   178 	if ( sem ) {

   179 	  tryagain:

   180 #ifdef __IRIX__

   181 		semval = semctl(sem->id, 0, GETVAL);

   182 #else

   183 		{

   184 		union semun arg;

   185 		arg.val = 0;

   186 		semval = semctl(sem->id, 0, GETVAL, arg);

   187 		}

   188 #endif

   189 		if ( semval < 0 ) {

   190 			if ( errno == EINTR ) {

   191 				goto tryagain;

   192 			}

   193 		} else {

   194 			value = (Uint32)semval;

   195 		}

   196 	}

   197 	return value;

   198 }

   199 

   200 int SDL_SemPost(SDL_sem *sem)

   201 {

   202 	int retval;

   203 

   204 	if ( ! sem ) {

   205 		SDL_SetError("Passed a NULL semaphore");

   206 		return -1;

   207 	}

   208 

   209 	retval = 0;

   210   tryagain:

   211 	if ( semop(sem->id, op_post, 1) < 0 ) {

   212 		if ( errno == EINTR ) {

   213 			goto tryagain;

   214 		}

   215 		SDL_SetError("Semaphore operation error");

   216 		retval = -1;

   217 	}

   218 	return retval;

   219 }