Atlas - SDL_syssem.c
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1/*
2  Simple DirectMedia Layer
3  Copyright (C) 1997-2025 Sam Lantinga <[email protected]>
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#include <errno.h>
24#include <pthread.h>
25#include <semaphore.h>
26#include <sys/time.h>
27#include <time.h>
28
29// Wrapper around POSIX 1003.1b semaphores
30
31#if defined(SDL_PLATFORM_MACOS) || defined(SDL_PLATFORM_IOS)
32// macOS doesn't support sem_getvalue() as of version 10.4
33#include "../generic/SDL_syssem.c"
34#else
35
36struct SDL_Semaphore
37{
38    sem_t sem;
39};
40
41// Create a semaphore, initialized with value
42SDL_Semaphore *SDL_CreateSemaphore(Uint32 initial_value)
43{
44    SDL_Semaphore *sem = (SDL_Semaphore *)SDL_malloc(sizeof(SDL_Semaphore));
45    if (sem) {
46        if (sem_init(&sem->sem, 0, initial_value) < 0) {
47            SDL_SetError("sem_init() failed");
48            SDL_free(sem);
49            sem = NULL;
50        }
51    }
52    return sem;
53}
54
55void SDL_DestroySemaphore(SDL_Semaphore *sem)
56{
57    if (sem) {
58        sem_destroy(&sem->sem);
59        SDL_free(sem);
60    }
61}
62
63bool SDL_WaitSemaphoreTimeoutNS(SDL_Semaphore *sem, Sint64 timeoutNS)
64{
65#ifdef HAVE_SEM_TIMEDWAIT
66#ifndef HAVE_CLOCK_GETTIME
67    struct timeval now;
68#endif
69    struct timespec ts_timeout;
70#else
71    Uint64 stop_time;
72#endif
73
74    if (!sem) {
75        return true;
76    }
77
78    // Try the easy cases first
79    if (timeoutNS == 0) {
80        return (sem_trywait(&sem->sem) == 0);
81    }
82
83    if (timeoutNS < 0) {
84        int rc;
85        do {
86            rc = sem_wait(&sem->sem);
87        } while (rc < 0 && errno == EINTR);
88
89        return (rc == 0);
90    }
91
92#ifdef HAVE_SEM_TIMEDWAIT
93    /* Setup the timeout. sem_timedwait doesn't wait for
94     * a lapse of time, but until we reach a certain time.
95     * This time is now plus the timeout.
96     */
97#ifdef HAVE_CLOCK_GETTIME
98    clock_gettime(CLOCK_REALTIME, &ts_timeout);
99
100    // Add our timeout to current time
101    ts_timeout.tv_sec += (timeoutNS / SDL_NS_PER_SECOND);
102    ts_timeout.tv_nsec += (timeoutNS % SDL_NS_PER_SECOND);
103#else
104    gettimeofday(&now, NULL);
105
106    // Add our timeout to current time
107    ts_timeout.tv_sec = now.tv_sec + (timeoutNS / SDL_NS_PER_SECOND);
108    ts_timeout.tv_nsec = SDL_US_TO_NS(now.tv_usec) + (timeoutNS % SDL_NS_PER_SECOND);
109#endif
110
111    // Wrap the second if needed
112    while (ts_timeout.tv_nsec >= 1000000000) {
113        ts_timeout.tv_sec += 1;
114        ts_timeout.tv_nsec -= 1000000000;
115    }
116
117    // Wait.
118    int rc;
119    do {
120        rc = sem_timedwait(&sem->sem, &ts_timeout);
121    } while (rc < 0 && errno == EINTR);
122
123    return (rc == 0);
124#else
125    stop_time = SDL_GetTicksNS() + timeoutNS;
126    while (sem_trywait(&sem->sem) != 0) {
127        if (SDL_GetTicksNS() >= stop_time) {
128            return false;
129        }
130        SDL_DelayNS(100);
131    }
132    return true;
133#endif // HAVE_SEM_TIMEDWAIT
134}
135
136Uint32 SDL_GetSemaphoreValue(SDL_Semaphore *sem)
137{
138    int ret = 0;
139
140    if (!sem) {
141        return 0;
142    }
143
144    sem_getvalue(&sem->sem, &ret);
145    if (ret < 0) {
146        ret = 0;
147    }
148    return (Uint32)ret;
149}
150
151void SDL_SignalSemaphore(SDL_Semaphore *sem)
152{
153    if (!sem) {
154        return;
155    }
156
157    sem_post(&sem->sem);
158}
159
160#endif // SDL_PLATFORM_MACOS
161
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