src/gallium/drivers/llvmpipe/lp_scene_queue.c

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   3  * Copyright 2009 VMware, Inc.
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  16  * of the Software.
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  27
  28
  29 /**
  30  * Scene queue.  We'll use two queues.  One contains "full" scenes which
  31  * are produced by the "setup" code.  The other contains "empty" scenes
  32  * which are produced by the "rast" code when it finishes rendering a scene.
  33  */
  34
  35 #include "os/os_thread.h"
  36 #include "util/u_memory.h"
  37 #include "lp_scene_queue.h"
  38 #include "util/u_math.h"
  39
  40
  41
  42 #define SCENE_QUEUE_SIZE 4
  43
  44
  45
  46 /**
  47  * A queue of scenes
  48  */
  49 struct lp_scene_queue
  50 {
  51    struct lp_scene *scenes[SCENE_QUEUE_SIZE];
  52
  53    mtx_t mutex;
  54    cnd_t change;
  55
  56    /* These values wrap around, so that head == tail means empty.  When used
  57     * to index the array, we use them modulo the queue size.  This scheme
  58     * works because the queue size is a power of two.
  59     */
  60    unsigned head;
  61    unsigned tail;
  62 };
  63
  64
  65
  66 /** Allocate a new scene queue */
  67 struct lp_scene_queue *
  68 lp_scene_queue_create(void)
  69 {
  70    /* Circular queue behavior depends on size being a power of two. */
  71    STATIC_ASSERT(SCENE_QUEUE_SIZE > 0);
  72    STATIC_ASSERT((SCENE_QUEUE_SIZE & (SCENE_QUEUE_SIZE - 1)) == 0);
  73
  74    struct lp_scene_queue *queue = CALLOC_STRUCT(lp_scene_queue);
  75
  76    if (!queue)
  77       return NULL;
  78
  79    (void) mtx_init(&queue->mutex, mtx_plain);
  80    cnd_init(&queue->change);
  81
  82    return queue;
  83 }
  84
  85
  86 /** Delete a scene queue */
  87 void
  88 lp_scene_queue_destroy(struct lp_scene_queue *queue)
  89 {
  90    cnd_destroy(&queue->change);
  91    mtx_destroy(&queue->mutex);
  92    FREE(queue);
  93 }
  94
  95
  96 /** Remove first lp_scene from head of queue */
  97 struct lp_scene *
  98 lp_scene_dequeue(struct lp_scene_queue *queue, boolean wait)
  99 {
 100    mtx_lock(&queue->mutex);
 101
 102    if (wait) {
 103       /* Wait for queue to be not empty. */
 104       while (queue->head == queue->tail)
 105          cnd_wait(&queue->change, &queue->mutex);
 106    } else {
 107       if (queue->head == queue->tail) {
 108          mtx_unlock(&queue->mutex);
 109          return NULL;
 110       }
 111    }
 112
 113    struct lp_scene *scene = queue->scenes[queue->head++ % SCENE_QUEUE_SIZE];
 114
 115    cnd_signal(&queue->change);
 116    mtx_unlock(&queue->mutex);
 117
 118    return scene;
 119 }
 120
 121
 122 /** Add an lp_scene to tail of queue */
 123 void
 124 lp_scene_enqueue(struct lp_scene_queue *queue, struct lp_scene *scene)
 125 {
 126    mtx_lock(&queue->mutex);
 127
 128    /* Wait for free space. */
 129    while (queue->tail - queue->head >= SCENE_QUEUE_SIZE)
 130       cnd_wait(&queue->change, &queue->mutex);
 131
 132    queue->scenes[queue->tail++ % SCENE_QUEUE_SIZE] = scene;
 133
 134    cnd_signal(&queue->change);
 135    mtx_unlock(&queue->mutex);
 136 }