SDL: src/thread/generic/SDL_sysmutex.c@d01593bd58d9

     1 /*

     2   Simple DirectMedia Layer

     3   Copyright (C) 1997-2021 Sam Lantinga <slouken@libsdl.org>

     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.

     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:

    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"

    23 /* An implementation of mutexes using semaphores */

    25 #include "SDL_thread.h"

    26 #include "SDL_systhread_c.h"

    29 struct SDL_mutex

    30 {

    31     int recursive;

    32     SDL_threadID owner;

    33     SDL_sem *sem;

    34 };

    36 /* Create a mutex */

    37 SDL_mutex *

    38 SDL_CreateMutex(void)

    39 {

    40     SDL_mutex *mutex;

    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 }

    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 }

    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;

    80     if (mutex == NULL) {

    81         return SDL_SetError("Passed a NULL mutex");

    82     }

    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     }

    97     return 0;

    98 #endif /* SDL_THREADS_DISABLED */

    99 }

   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;

   111     if (mutex == NULL) {

   112         return SDL_SetError("Passed a NULL mutex");

   113     }

   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     }

   130     return retval;

   131 #endif /* SDL_THREADS_DISABLED */

   132 }

   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     }

   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     }

   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 }

   165 /* vi: set ts=4 sw=4 expandtab: */

author	Ozkan Sezer
	Mon, 25 Jan 2021 04:11:40 +0300
changeset 14792	d01593bd58d9
parent 14640	b2b3343a310d
permissions	-rw-r--r--