src/thread/stdcpp/SDL_sysmutex.cpp
author David Ludwig
Thu, 22 Nov 2012 23:12:06 -0500
changeset 8357 8d788bb003f2
parent 8356 src/thread/stdcpp/SDL_sysmutex.c@4d85eba58f0a
child 8360 7f1bc00e59fc
permissions -rw-r--r--
WinRT: made the skeleton C++11 thread implementation use .cpp files, not .c
     1 /*
     2   Simple DirectMedia Layer
     3   Copyright (C) 1997-2012 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_config.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 extern "C"
    38 SDL_mutex *
    39 SDL_CreateMutex(void)
    40 {
    41     SDL_mutex *mutex;
    42 
    43     /* Allocate mutex memory */
    44     mutex = (SDL_mutex *) SDL_malloc(sizeof(*mutex));
    45     if (mutex) {
    46         /* Create the mutex semaphore, with initial value 1 */
    47         mutex->sem = SDL_CreateSemaphore(1);
    48         mutex->recursive = 0;
    49         mutex->owner = 0;
    50         if (!mutex->sem) {
    51             SDL_free(mutex);
    52             mutex = NULL;
    53         }
    54     } else {
    55         SDL_OutOfMemory();
    56     }
    57     return mutex;
    58 }
    59 
    60 /* Free the mutex */
    61 extern "C"
    62 void
    63 SDL_DestroyMutex(SDL_mutex * mutex)
    64 {
    65     if (mutex) {
    66         if (mutex->sem) {
    67             SDL_DestroySemaphore(mutex->sem);
    68         }
    69         SDL_free(mutex);
    70     }
    71 }
    72 
    73 /* Lock the semaphore */
    74 extern "C"
    75 int
    76 SDL_mutexP(SDL_mutex * mutex)
    77 {
    78 #if SDL_THREADS_DISABLED
    79     return 0;
    80 #else
    81     SDL_threadID this_thread;
    82 
    83     if (mutex == NULL) {
    84         SDL_SetError("Passed a NULL mutex");
    85         return -1;
    86     }
    87 
    88     this_thread = SDL_ThreadID();
    89     if (mutex->owner == this_thread) {
    90         ++mutex->recursive;
    91     } else {
    92         /* The order of operations is important.
    93            We set the locking thread id after we obtain the lock
    94            so unlocks from other threads will fail.
    95          */
    96         SDL_SemWait(mutex->sem);
    97         mutex->owner = this_thread;
    98         mutex->recursive = 0;
    99     }
   100 
   101     return 0;
   102 #endif /* SDL_THREADS_DISABLED */
   103 }
   104 
   105 /* Unlock the mutex */
   106 extern "C"
   107 int
   108 SDL_mutexV(SDL_mutex * mutex)
   109 {
   110 #if SDL_THREADS_DISABLED
   111     return 0;
   112 #else
   113     if (mutex == NULL) {
   114         SDL_SetError("Passed a NULL mutex");
   115         return -1;
   116     }
   117 
   118     /* If we don't own the mutex, we can't unlock it */
   119     if (SDL_ThreadID() != mutex->owner) {
   120         SDL_SetError("mutex not owned by this thread");
   121         return -1;
   122     }
   123 
   124     if (mutex->recursive) {
   125         --mutex->recursive;
   126     } else {
   127         /* The order of operations is important.
   128            First reset the owner so another thread doesn't lock
   129            the mutex and set the ownership before we reset it,
   130            then release the lock semaphore.
   131          */
   132         mutex->owner = 0;
   133         SDL_SemPost(mutex->sem);
   134     }
   135     return 0;
   136 #endif /* SDL_THREADS_DISABLED */
   137 }
   138 
   139 /* vi: set ts=4 sw=4 expandtab: */