src/thread/generic/SDL_sysmutex.c
author Ryan C. Gordon <icculus@icculus.org>
Thu, 18 Dec 2014 00:19:52 -0500
changeset 9278 8900afb78a19
parent 8149 681eb46b8ac4
child 9619 b94b6d0bff0f
permissions -rw-r--r--
Initial merge of Emscripten port!

With this commit, you can compile SDL2 with Emscripten
( http://emscripten.org/ ), and make your SDL-based C/C++ program
into a web app.

This port was due to the efforts of several people, including: Charlie Birks,
Sathyanarayanan Gunasekaran, Jukka Jylänki, Alon Zakai, Edward Rudd,
Bruce Mitchener, and Martin Gerhardy. (Thanks, everyone!)
     1 /*
     2   Simple DirectMedia Layer
     3   Copyright (C) 1997-2014 Sam Lantinga <slouken@libsdl.org>
     4 
     5   This software is provided 'as-is', without any express or implied
     6   warranty.  In no event will the authors be held liable for any damages
     7   arising from the use of this software.
     8 
     9   Permission is granted to anyone to use this software for any purpose,
    10   including commercial applications, and to alter it and redistribute it
    11   freely, subject to the following restrictions:
    12 
    13   1. The origin of this software must not be misrepresented; you must not
    14      claim that you wrote the original software. If you use this software
    15      in a product, an acknowledgment in the product documentation would be
    16      appreciated but is not required.
    17   2. Altered source versions must be plainly marked as such, and must not be
    18      misrepresented as being the original software.
    19   3. This notice may not be removed or altered from any source distribution.
    20 */
    21 #include "../../SDL_internal.h"
    22 
    23 /* An implementation of mutexes using semaphores */
    24 
    25 #include "SDL_thread.h"
    26 #include "SDL_systhread_c.h"
    27 
    28 
    29 struct SDL_mutex
    30 {
    31     int recursive;
    32     SDL_threadID owner;
    33     SDL_sem *sem;
    34 };
    35 
    36 /* Create a mutex */
    37 SDL_mutex *
    38 SDL_CreateMutex(void)
    39 {
    40     SDL_mutex *mutex;
    41 
    42     /* Allocate mutex memory */
    43     mutex = (SDL_mutex *) SDL_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             SDL_free(mutex);
    51             mutex = NULL;
    52         }
    53     } else {
    54         SDL_OutOfMemory();
    55     }
    56     return mutex;
    57 }
    58 
    59 /* Free the mutex */
    60 void
    61 SDL_DestroyMutex(SDL_mutex * mutex)
    62 {
    63     if (mutex) {
    64         if (mutex->sem) {
    65             SDL_DestroySemaphore(mutex->sem);
    66         }
    67         SDL_free(mutex);
    68     }
    69 }
    70 
    71 /* Lock the mutex */
    72 int
    73 SDL_LockMutex(SDL_mutex * mutex)
    74 {
    75 #if SDL_THREADS_DISABLED
    76     return 0;
    77 #else
    78     SDL_threadID this_thread;
    79 
    80     if (mutex == NULL) {
    81         return SDL_SetError("Passed a NULL mutex");
    82     }
    83 
    84     this_thread = SDL_ThreadID();
    85     if (mutex->owner == this_thread) {
    86         ++mutex->recursive;
    87     } else {
    88         /* The order of operations is important.
    89            We set the locking thread id after we obtain the lock
    90            so unlocks from other threads will fail.
    91          */
    92         SDL_SemWait(mutex->sem);
    93         mutex->owner = this_thread;
    94         mutex->recursive = 0;
    95     }
    96 
    97     return 0;
    98 #endif /* SDL_THREADS_DISABLED */
    99 }
   100 
   101 /* try Lock the mutex */
   102 int
   103 SDL_TryLockMutex(SDL_mutex * mutex)
   104 {
   105 #if SDL_THREADS_DISABLED
   106     return 0;
   107 #else
   108     int retval = 0;
   109     SDL_threadID this_thread;
   110 
   111     if (mutex == NULL) {
   112         return SDL_SetError("Passed a NULL mutex");
   113     }
   114 
   115     this_thread = SDL_ThreadID();
   116     if (mutex->owner == this_thread) {
   117         ++mutex->recursive;
   118     } else {
   119         /* The order of operations is important.
   120          We set the locking thread id after we obtain the lock
   121          so unlocks from other threads will fail.
   122          */
   123         retval = SDL_SemWait(mutex->sem);
   124         if (retval == 0) {
   125             mutex->owner = this_thread;
   126             mutex->recursive = 0;
   127         }
   128     }
   129 
   130     return retval;
   131 #endif /* SDL_THREADS_DISABLED */
   132 }
   133 
   134 /* Unlock the mutex */
   135 int
   136 SDL_mutexV(SDL_mutex * mutex)
   137 {
   138 #if SDL_THREADS_DISABLED
   139     return 0;
   140 #else
   141     if (mutex == NULL) {
   142         return SDL_SetError("Passed a NULL mutex");
   143     }
   144 
   145     /* If we don't own the mutex, we can't unlock it */
   146     if (SDL_ThreadID() != mutex->owner) {
   147         return SDL_SetError("mutex not owned by this thread");
   148     }
   149 
   150     if (mutex->recursive) {
   151         --mutex->recursive;
   152     } else {
   153         /* The order of operations is important.
   154            First reset the owner so another thread doesn't lock
   155            the mutex and set the ownership before we reset it,
   156            then release the lock semaphore.
   157          */
   158         mutex->owner = 0;
   159         SDL_SemPost(mutex->sem);
   160     }
   161     return 0;
   162 #endif /* SDL_THREADS_DISABLED */
   163 }
   164 
   165 /* vi: set ts=4 sw=4 expandtab: */