Atlas - SDL_syssem.c
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[FILE BEGIN]
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#ifdef SDL_THREAD_N3DS
24
25// An implementation of semaphores using libctru's LightSemaphore
26
27#include <3ds.h>
28
29struct SDL_Semaphore
30{
31    LightSemaphore semaphore;
32};
33
34SDL_Semaphore *SDL_CreateSemaphore(Uint32 initial_value)
35{
36    SDL_Semaphore *sem;
37
38    if (initial_value > SDL_MAX_SINT16) {
39        SDL_SetError("Initial semaphore value too high for this platform");
40        return NULL;
41    }
42
43    sem = (SDL_Semaphore *)SDL_malloc(sizeof(*sem));
44    if (!sem) {
45        return NULL;
46    }
47
48    LightSemaphore_Init(&sem->semaphore, initial_value, SDL_MAX_SINT16);
49
50    return sem;
51}
52
53/* WARNING:
54   You cannot call this function when another thread is using the semaphore.
55*/
56void SDL_DestroySemaphore(SDL_Semaphore *sem)
57{
58    SDL_free(sem);
59}
60
61static bool WaitOnSemaphoreFor(SDL_Semaphore *sem, Sint64 timeoutNS)
62{
63    Uint64 stop_time = SDL_GetTicksNS() + timeoutNS;
64    while (SDL_GetTicksNS() < stop_time) {
65        if (LightSemaphore_TryAcquire(&sem->semaphore, 1) == 0) {
66            return true;
67        }
68        // 100 microseconds seems to be the sweet spot
69        SDL_DelayNS(SDL_US_TO_NS(100));
70    }
71
72    // If we failed, yield to avoid starvation on busy waits
73    SDL_DelayNS(1);
74    return false;
75}
76
77bool SDL_WaitSemaphoreTimeoutNS(SDL_Semaphore *sem, Sint64 timeoutNS)
78{
79    if (!sem) {
80        return true;
81    }
82
83    if (timeoutNS < 0) { // -1 == wait indefinitely.
84        LightSemaphore_Acquire(&sem->semaphore, 1);
85        return true;
86    }
87
88    if (LightSemaphore_TryAcquire(&sem->semaphore, 1) == 0) {
89        return true;
90    }
91
92    return WaitOnSemaphoreFor(sem, timeoutNS);
93}
94
95Uint32 SDL_GetSemaphoreValue(SDL_Semaphore *sem)
96{
97    if (!sem) {
98        return 0;
99    }
100    return sem->semaphore.current_count;
101}
102
103void SDL_SignalSemaphore(SDL_Semaphore *sem)
104{
105    if (!sem) {
106        return;
107    }
108
109    LightSemaphore_Release(&sem->semaphore, 1);
110}
111
112#endif // SDL_THREAD_N3DS
113
[FILE END]
(C) 2025 0x4248
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