src/thread/generic/SDL_sysmutex.c
author Sam Lantinga
Mon, 06 Feb 2006 08:28:51 +0000
changeset 1330 450721ad5436
parent 1312 c9b51268668f
child 1336 3692456e7b0f
permissions -rw-r--r--
It's now possible to build SDL without any C runtime at all on Windows,
using Visual C++ 2005
     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 
    23 /* An implementation of mutexes using semaphores */
    24 
    25 #include "SDL_error.h"
    26 #include "SDL_thread.h"
    27 #include "SDL_stdlib.h"
    28 #include "SDL_systhread_c.h"
    29 
    30 
    31 struct SDL_mutex {
    32 	int recursive;
    33 	Uint32 owner;
    34 	SDL_sem *sem;
    35 };
    36 
    37 /* Create a mutex */
    38 SDL_mutex *SDL_CreateMutex(void)
    39 {
    40 	SDL_mutex *mutex;
    41 
    42 	/* Allocate mutex memory */
    43 	mutex = (SDL_mutex *)malloc(sizeof(*mutex));
    44 	if ( mutex ) {
    45 		/* Create the mutex semaphore, with initial value 1 */
    46 		mutex->sem = SDL_CreateSemaphore(1);
    47 		mutex->recursive = 0;
    48 		mutex->owner = 0;
    49 		if ( ! mutex->sem ) {
    50 			free(mutex);
    51 			mutex = NULL;
    52 		}
    53 	} else {
    54 		SDL_OutOfMemory();
    55 	}
    56 	return mutex;
    57 }
    58 
    59 /* Free the mutex */
    60 void SDL_DestroyMutex(SDL_mutex *mutex)
    61 {
    62 	if ( mutex ) {
    63 		if ( mutex->sem ) {
    64 			SDL_DestroySemaphore(mutex->sem);
    65 		}
    66 		free(mutex);
    67 	}
    68 }
    69 
    70 /* Lock the semaphore */
    71 int SDL_mutexP(SDL_mutex *mutex)
    72 {
    73 #ifdef DISABLE_THREADS
    74 	return 0;
    75 #else
    76 	Uint32 this_thread;
    77 
    78 	if ( mutex == NULL ) {
    79 		SDL_SetError("Passed a NULL mutex");
    80 		return -1;
    81 	}
    82 
    83 	this_thread = SDL_ThreadID();
    84 	if ( mutex->owner == this_thread ) {
    85 		++mutex->recursive;
    86 	} else {
    87 		/* The order of operations is important.
    88 		   We set the locking thread id after we obtain the lock
    89 		   so unlocks from other threads will fail.
    90 		*/
    91 		SDL_SemWait(mutex->sem);
    92 		mutex->owner = this_thread;
    93 		mutex->recursive = 0;
    94 	}
    95 
    96 	return 0;
    97 #endif /* DISABLE_THREADS */
    98 }
    99 
   100 /* Unlock the mutex */
   101 int SDL_mutexV(SDL_mutex *mutex)
   102 {
   103 #ifdef DISABLE_THREADS
   104 	return 0;
   105 #else
   106 	if ( mutex == NULL ) {
   107 		SDL_SetError("Passed a NULL mutex");
   108 		return -1;
   109 	}
   110 
   111 	/* If we don't own the mutex, we can't unlock it */
   112 	if ( SDL_ThreadID() != mutex->owner ) {
   113 		SDL_SetError("mutex not owned by this thread");
   114 		return -1;
   115 	}
   116 
   117 	if ( mutex->recursive ) {
   118 		--mutex->recursive;
   119 	} else {
   120 		/* The order of operations is important.
   121 		   First reset the owner so another thread doesn't lock
   122 		   the mutex and set the ownership before we reset it,
   123 		   then release the lock semaphore.
   124 		 */
   125 		mutex->owner = 0;
   126 		SDL_SemPost(mutex->sem);
   127 	}
   128 	return 0;
   129 #endif /* DISABLE_THREADS */
   130 }