Atlas - SDL_dos_scheduler.h
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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
22#ifndef SDL_dos_scheduler_h_
23#define SDL_dos_scheduler_h_
24
25#include "SDL_internal.h"
26#include <setjmp.h>
27
28#ifdef __cplusplus
29extern "C" {
30#endif
31
32// Maximum number of cooperative threads. DOS doesn't need many —
33// typically just main thread + audio thread + maybe a loading thread.
34#define DOS_MAX_THREADS 16
35
36// Default stack size for new threads (64 KB)
37#define DOS_DEFAULT_STACK_SIZE (64 * 1024)
38
39// Thread states
40typedef enum
41{
42    DOS_THREAD_FREE = 0, // Slot is available
43    DOS_THREAD_READY,    // Runnable
44    DOS_THREAD_RUNNING,  // Currently executing
45    DOS_THREAD_BLOCKED,  // Waiting on a semaphore/mutex
46    DOS_THREAD_FINISHED  // Thread function returned
47} DOS_ThreadState;
48
49// Per-thread context
50typedef struct DOS_ThreadContext
51{
52    jmp_buf env; // Saved CPU state for context switch
53    DOS_ThreadState state;
54    int id;           // Thread ID (index into thread table)
55    void *stack_base; // malloc'd stack memory
56    size_t stack_size;
57    int exit_status; // Return value from thread function
58
59    // Entry point
60    int (*entry_fn)(void *);
61    void *entry_arg;
62
63    // Join support
64    volatile bool finished; // Set when thread function returns
65    int join_waiter;        // ID of thread waiting in WaitThread, or -1
66} DOS_ThreadContext;
67
68// Initialize the scheduler. Must be called before any thread operations.
69// Registers the calling context as thread 0 (the main thread).
70void DOS_SchedulerInit(void);
71
72// Shut down the scheduler.
73void DOS_SchedulerQuit(void);
74
75// Create a new thread. Returns thread ID (>0) on success, -1 on failure.
76// The thread starts in READY state and will run when yielded to.
77int DOS_CreateThread(int (*fn)(void *), void *arg, size_t stack_size);
78
79// Yield the current thread's timeslice. Switches to the next runnable thread
80// using round-robin scheduling. If no other thread is runnable, returns
81// immediately (no-op). This is the core cooperative scheduling primitive.
82void DOS_Yield(void);
83
84// Mark a thread as finished and yield. Called when a thread's entry
85// function returns.
86void DOS_ExitThread(int status);
87
88// Block until the specified thread finishes. Returns the thread's exit status.
89int DOS_JoinThread(int thread_id);
90
91// Get the current thread's ID.
92int DOS_GetCurrentThreadID(void);
93
94// Mark a thread as READY (used by semaphore signal to wake a blocked thread).
95void DOS_WakeThread(int thread_id);
96
97// Mark the current thread as BLOCKED and yield (used by semaphore wait).
98void DOS_BlockCurrentThread(void);
99
100// Destroy a thread's resources (stack, etc). Thread must be FINISHED or FREE.
101void DOS_DestroyThread(int thread_id);
102
103#ifdef __cplusplus
104}
105#endif
106
107#endif // SDL_dos_scheduler_h_
108
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