Atlas - SDL_syssem.c
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[FILE BEGIN]
1/*
2  Simple DirectMedia Layer
3  Copyright (C) 1997-2026 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_DOS
24
25/* Semaphore implementation for DOS cooperative threading.
26   Uses cli/sti for atomicity and cooperative yielding for waits. */
27
28#include "../../core/dos/SDL_dos.h"
29#include "../../core/dos/SDL_dos_scheduler.h"
30
31struct SDL_Semaphore
32{
33    volatile Uint32 count;
34};
35
36SDL_Semaphore *SDL_CreateSemaphore(Uint32 initial_value)
37{
38    SDL_Semaphore *sem = (SDL_Semaphore *)SDL_malloc(sizeof(*sem));
39    if (sem) {
40        sem->count = initial_value;
41    }
42    return sem;
43}
44
45void SDL_DestroySemaphore(SDL_Semaphore *sem)
46{
47    if (sem) {
48        SDL_free(sem);
49    }
50}
51
52bool SDL_WaitSemaphoreTimeoutNS(SDL_Semaphore *sem, Sint64 timeoutNS)
53{
54    if (!sem) {
55        return true;
56    }
57
58    /* Try-wait (poll): check and decrement if possible */
59    if (timeoutNS == 0) {
60        bool acquired = false;
61        DOS_DisableInterrupts();
62        if (sem->count > 0) {
63            sem->count--;
64            acquired = true;
65        }
66        DOS_EnableInterrupts();
67        return acquired;
68    }
69
70    /* Indefinite wait (-1) or timed wait */
71    Uint64 deadline = 0;
72    if (timeoutNS > 0) {
73        deadline = SDL_GetPerformanceCounter() +
74                   (Uint64)((double)timeoutNS * (double)SDL_GetPerformanceFrequency() / 1e9);
75    }
76
77    for (;;) {
78        DOS_DisableInterrupts();
79        if (sem->count > 0) {
80            sem->count--;
81            DOS_EnableInterrupts();
82            return true; /* Acquired */
83        }
84        DOS_EnableInterrupts();
85
86        /* Check timeout */
87        if (timeoutNS > 0 && SDL_GetPerformanceCounter() >= deadline) {
88            return false; /* Timed out */
89        }
90
91        /* Yield to other threads instead of busy-spinning */
92        DOS_Yield();
93    }
94}
95
96Uint32 SDL_GetSemaphoreValue(SDL_Semaphore *sem)
97{
98    if (!sem) {
99        return 0;
100    }
101    return sem->count;
102}
103
104void SDL_SignalSemaphore(SDL_Semaphore *sem)
105{
106    if (!sem) {
107        return;
108    }
109
110    DOS_DisableInterrupts();
111    sem->count++;
112    DOS_EnableInterrupts();
113}
114
115#endif /* SDL_THREAD_DOS */
116
[FILE END]
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