cscg22-gearboy

CSCG 2022 Challenge 'Gearboy'
git clone https://git.sinitax.com/sinitax/cscg22-gearboy
Log | Files | Refs | sfeed.txt

SDL_syscond.c (6195B)


      1/*
      2  Simple DirectMedia Layer
      3  Copyright (C) 1997-2014 Sam Lantinga <slouken@libsdl.org>
      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/* An implementation of condition variables using semaphores and mutexes */
     24/*
     25   This implementation borrows heavily from the BeOS condition variable
     26   implementation, written by Christopher Tate and Owen Smith.  Thanks!
     27 */
     28
     29#include "SDL_thread.h"
     30
     31struct SDL_cond
     32{
     33    SDL_mutex *lock;
     34    int waiting;
     35    int signals;
     36    SDL_sem *wait_sem;
     37    SDL_sem *wait_done;
     38};
     39
     40/* Create a condition variable */
     41SDL_cond *
     42SDL_CreateCond(void)
     43{
     44    SDL_cond *cond;
     45
     46    cond = (SDL_cond *) SDL_malloc(sizeof(SDL_cond));
     47    if (cond) {
     48        cond->lock = SDL_CreateMutex();
     49        cond->wait_sem = SDL_CreateSemaphore(0);
     50        cond->wait_done = SDL_CreateSemaphore(0);
     51        cond->waiting = cond->signals = 0;
     52        if (!cond->lock || !cond->wait_sem || !cond->wait_done) {
     53            SDL_DestroyCond(cond);
     54            cond = NULL;
     55        }
     56    } else {
     57        SDL_OutOfMemory();
     58    }
     59    return (cond);
     60}
     61
     62/* Destroy a condition variable */
     63void
     64SDL_DestroyCond(SDL_cond * cond)
     65{
     66    if (cond) {
     67        if (cond->wait_sem) {
     68            SDL_DestroySemaphore(cond->wait_sem);
     69        }
     70        if (cond->wait_done) {
     71            SDL_DestroySemaphore(cond->wait_done);
     72        }
     73        if (cond->lock) {
     74            SDL_DestroyMutex(cond->lock);
     75        }
     76        SDL_free(cond);
     77    }
     78}
     79
     80/* Restart one of the threads that are waiting on the condition variable */
     81int
     82SDL_CondSignal(SDL_cond * cond)
     83{
     84    if (!cond) {
     85        return SDL_SetError("Passed a NULL condition variable");
     86    }
     87
     88    /* If there are waiting threads not already signalled, then
     89       signal the condition and wait for the thread to respond.
     90     */
     91    SDL_LockMutex(cond->lock);
     92    if (cond->waiting > cond->signals) {
     93        ++cond->signals;
     94        SDL_SemPost(cond->wait_sem);
     95        SDL_UnlockMutex(cond->lock);
     96        SDL_SemWait(cond->wait_done);
     97    } else {
     98        SDL_UnlockMutex(cond->lock);
     99    }
    100
    101    return 0;
    102}
    103
    104/* Restart all threads that are waiting on the condition variable */
    105int
    106SDL_CondBroadcast(SDL_cond * cond)
    107{
    108    if (!cond) {
    109        return SDL_SetError("Passed a NULL condition variable");
    110    }
    111
    112    /* If there are waiting threads not already signalled, then
    113       signal the condition and wait for the thread to respond.
    114     */
    115    SDL_LockMutex(cond->lock);
    116    if (cond->waiting > cond->signals) {
    117        int i, num_waiting;
    118
    119        num_waiting = (cond->waiting - cond->signals);
    120        cond->signals = cond->waiting;
    121        for (i = 0; i < num_waiting; ++i) {
    122            SDL_SemPost(cond->wait_sem);
    123        }
    124        /* Now all released threads are blocked here, waiting for us.
    125           Collect them all (and win fabulous prizes!) :-)
    126         */
    127        SDL_UnlockMutex(cond->lock);
    128        for (i = 0; i < num_waiting; ++i) {
    129            SDL_SemWait(cond->wait_done);
    130        }
    131    } else {
    132        SDL_UnlockMutex(cond->lock);
    133    }
    134
    135    return 0;
    136}
    137
    138/* Wait on the condition variable for at most 'ms' milliseconds.
    139   The mutex must be locked before entering this function!
    140   The mutex is unlocked during the wait, and locked again after the wait.
    141
    142Typical use:
    143
    144Thread A:
    145    SDL_LockMutex(lock);
    146    while ( ! condition ) {
    147        SDL_CondWait(cond, lock);
    148    }
    149    SDL_UnlockMutex(lock);
    150
    151Thread B:
    152    SDL_LockMutex(lock);
    153    ...
    154    condition = true;
    155    ...
    156    SDL_CondSignal(cond);
    157    SDL_UnlockMutex(lock);
    158 */
    159int
    160SDL_CondWaitTimeout(SDL_cond * cond, SDL_mutex * mutex, Uint32 ms)
    161{
    162    int retval;
    163
    164    if (!cond) {
    165        return SDL_SetError("Passed a NULL condition variable");
    166    }
    167
    168    /* Obtain the protection mutex, and increment the number of waiters.
    169       This allows the signal mechanism to only perform a signal if there
    170       are waiting threads.
    171     */
    172    SDL_LockMutex(cond->lock);
    173    ++cond->waiting;
    174    SDL_UnlockMutex(cond->lock);
    175
    176    /* Unlock the mutex, as is required by condition variable semantics */
    177    SDL_UnlockMutex(mutex);
    178
    179    /* Wait for a signal */
    180    if (ms == SDL_MUTEX_MAXWAIT) {
    181        retval = SDL_SemWait(cond->wait_sem);
    182    } else {
    183        retval = SDL_SemWaitTimeout(cond->wait_sem, ms);
    184    }
    185
    186    /* Let the signaler know we have completed the wait, otherwise
    187       the signaler can race ahead and get the condition semaphore
    188       if we are stopped between the mutex unlock and semaphore wait,
    189       giving a deadlock.  See the following URL for details:
    190       http://www-classic.be.com/aboutbe/benewsletter/volume_III/Issue40.html
    191     */
    192    SDL_LockMutex(cond->lock);
    193    if (cond->signals > 0) {
    194        /* If we timed out, we need to eat a condition signal */
    195        if (retval > 0) {
    196            SDL_SemWait(cond->wait_sem);
    197        }
    198        /* We always notify the signal thread that we are done */
    199        SDL_SemPost(cond->wait_done);
    200
    201        /* Signal handshake complete */
    202        --cond->signals;
    203    }
    204    --cond->waiting;
    205    SDL_UnlockMutex(cond->lock);
    206
    207    /* Lock the mutex, as is required by condition variable semantics */
    208    SDL_LockMutex(mutex);
    209
    210    return retval;
    211}
    212
    213/* Wait on the condition variable forever */
    214int
    215SDL_CondWait(SDL_cond * cond, SDL_mutex * mutex)
    216{
    217    return SDL_CondWaitTimeout(cond, mutex, SDL_MUTEX_MAXWAIT);
    218}
    219
    220/* vi: set ts=4 sw=4 expandtab: */