SDL 2.0
SDL_syscond.c File Reference
#include "../../SDL_internal.h"
#include <sys/time.h>
#include <time.h>
#include <unistd.h>
#include <errno.h>
#include <pthread.h>
#include "SDL_thread.h"
#include "SDL_sysmutex_c.h"
+ Include dependency graph for SDL_syscond.c:

Go to the source code of this file.

Data Structures

struct  SDL_cond
 

Functions

SDL_condSDL_CreateCond (void)
 
void SDL_DestroyCond (SDL_cond *cond)
 
int SDL_CondSignal (SDL_cond *cond)
 
int SDL_CondBroadcast (SDL_cond *cond)
 
int SDL_CondWaitTimeout (SDL_cond *cond, SDL_mutex *mutex, Uint32 ms)
 
int SDL_CondWait (SDL_cond *cond, SDL_mutex *mutex)
 

Function Documentation

◆ SDL_CondBroadcast()

int SDL_CondBroadcast ( SDL_cond cond)

Restart all threads that are waiting on the condition variable.

Returns
0 or -1 on error.

Definition at line 83 of file SDL_syscond.c.

84{
85 int retval;
86
87 if (!cond) {
88 return SDL_SetError("Passed a NULL condition variable");
89 }
90
91 retval = 0;
92 if (pthread_cond_broadcast(&cond->cond) != 0) {
93 return SDL_SetError("pthread_cond_broadcast() failed");
94 }
95 return retval;
96}
#define SDL_SetError
pthread_cond_t cond
Definition: SDL_syscond.c:34
SDL_bool retval

References SDL_cond::cond, retval, and SDL_SetError.

◆ SDL_CondSignal()

int SDL_CondSignal ( SDL_cond cond)

Restart one of the threads that are waiting on the condition variable.

Returns
0 or -1 on error.

Definition at line 66 of file SDL_syscond.c.

67{
68 int retval;
69
70 if (!cond) {
71 return SDL_SetError("Passed a NULL condition variable");
72 }
73
74 retval = 0;
75 if (pthread_cond_signal(&cond->cond) != 0) {
76 return SDL_SetError("pthread_cond_signal() failed");
77 }
78 return retval;
79}

References SDL_cond::cond, retval, and SDL_SetError.

◆ SDL_CondWait()

int SDL_CondWait ( SDL_cond cond,
SDL_mutex mutex 
)

Wait on the condition variable, unlocking the provided mutex.

Warning
The mutex must be locked before entering this function!

The mutex is re-locked once the condition variable is signaled.

Returns
0 when it is signaled, or -1 on error.

Definition at line 148 of file SDL_syscond.c.

149{
150 if (!cond) {
151 return SDL_SetError("Passed a NULL condition variable");
152 } else if (pthread_cond_wait(&cond->cond, &mutex->id) != 0) {
153 return SDL_SetError("pthread_cond_wait() failed");
154 }
155 return 0;
156}
pthread_mutex_t id
Definition: SDL_sysmutex.c:35
static SDL_mutex * mutex
Definition: testlock.c:23

References SDL_cond::cond, SDL_mutex::id, mutex, and SDL_SetError.

◆ SDL_CondWaitTimeout()

int SDL_CondWaitTimeout ( SDL_cond cond,
SDL_mutex mutex,
Uint32  ms 
)

Waits for at most ms milliseconds, and returns 0 if the condition variable is signaled, SDL_MUTEX_TIMEDOUT if the condition is not signaled in the allotted time, and -1 on error.

Warning
On some platforms this function is implemented by looping with a delay of 1 ms, and so should be avoided if possible.

Definition at line 99 of file SDL_syscond.c.

100{
101 int retval;
102#ifndef HAVE_CLOCK_GETTIME
103 struct timeval delta;
104#endif
105 struct timespec abstime;
106
107 if (!cond) {
108 return SDL_SetError("Passed a NULL condition variable");
109 }
110
111#ifdef HAVE_CLOCK_GETTIME
112 clock_gettime(CLOCK_REALTIME, &abstime);
113
114 abstime.tv_nsec += (ms % 1000) * 1000000;
115 abstime.tv_sec += ms / 1000;
116#else
117 gettimeofday(&delta, NULL);
118
119 abstime.tv_sec = delta.tv_sec + (ms / 1000);
120 abstime.tv_nsec = (delta.tv_usec + (ms % 1000) * 1000) * 1000;
121#endif
122 if (abstime.tv_nsec > 1000000000) {
123 abstime.tv_sec += 1;
124 abstime.tv_nsec -= 1000000000;
125 }
126
127 tryagain:
128 retval = pthread_cond_timedwait(&cond->cond, &mutex->id, &abstime);
129 switch (retval) {
130 case EINTR:
131 goto tryagain;
132 /* break; -Wunreachable-code-break */
133 case ETIMEDOUT:
135 break;
136 case 0:
137 break;
138 default:
139 retval = SDL_SetError("pthread_cond_timedwait() failed");
140 }
141 return retval;
142}
#define SDL_MUTEX_TIMEDOUT
Definition: SDL_mutex.h:44
#define NULL
Definition: begin_code.h:167

References SDL_cond::cond, SDL_mutex::id, mutex, NULL, retval, SDL_MUTEX_TIMEDOUT, and SDL_SetError.

◆ SDL_CreateCond()

SDL_cond * SDL_CreateCond ( void  )

Create a condition variable.

Typical use of condition variables:

Thread A: SDL_LockMutex(lock); while ( ! condition ) { SDL_CondWait(cond, lock); } SDL_UnlockMutex(lock);

Thread B: SDL_LockMutex(lock); ... condition = true; ... SDL_CondSignal(cond); SDL_UnlockMutex(lock);

There is some discussion whether to signal the condition variable with the mutex locked or not. There is some potential performance benefit to unlocking first on some platforms, but there are some potential race conditions depending on how your code is structured.

In general it's safer to signal the condition variable while the mutex is locked.

Definition at line 39 of file SDL_syscond.c.

40{
41 SDL_cond *cond;
42
43 cond = (SDL_cond *) SDL_malloc(sizeof(SDL_cond));
44 if (cond) {
45 if (pthread_cond_init(&cond->cond, NULL) != 0) {
46 SDL_SetError("pthread_cond_init() failed");
47 SDL_free(cond);
48 cond = NULL;
49 }
50 }
51 return (cond);
52}
#define SDL_malloc
#define SDL_free

References SDL_cond::cond, NULL, SDL_free, SDL_malloc, and SDL_SetError.

◆ SDL_DestroyCond()

void SDL_DestroyCond ( SDL_cond cond)

Destroy a condition variable.

Definition at line 56 of file SDL_syscond.c.

57{
58 if (cond) {
59 pthread_cond_destroy(&cond->cond);
60 SDL_free(cond);
61 }
62}

References SDL_cond::cond, and SDL_free.