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Added SDL_ReserveSpaceInDataQueue() to make space without copying data.

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This commit is contained in:
Ryan C. Gordon 2016-12-27 23:48:43 -05:00
parent 18d9b23c65
commit 2e2572a4f1
2 changed files with 103 additions and 34 deletions
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122
src/SDL_dataqueue.c
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@ -137,6 +137,40 @@ SDL_ClearDataQueue(SDL_DataQueue *queue, const size_t slack)
SDL_FreeDataQueueList(packet); /* free extra packets */
}
static SDL_DataQueuePacket *
AllocateDataQueuePacket(SDL_DataQueue *queue)
{
SDL_DataQueuePacket *packet;
SDL_assert(queue != NULL);
packet = queue->pool;
if (packet != NULL) {
/* we have one available in the pool. */
queue->pool = packet->next;
} else {
/* Have to allocate a new one! */
packet = (SDL_DataQueuePacket *) SDL_malloc(sizeof (SDL_DataQueuePacket) + queue->packet_size);
if (packet == NULL) {
return NULL;
}
}
packet->datalen = 0;
packet->startpos = 0;
packet->next = NULL;
SDL_assert((queue->head != NULL) == (queue->queued_bytes != 0));
if (queue->tail == NULL) {
queue->head = packet;
} else {
queue->tail->next = packet;
}
queue->tail = packet;
return packet;
}
int
SDL_WriteToDataQueue(SDL_DataQueue *queue, const void *_data, const size_t _len)
{
@ -161,42 +195,23 @@ SDL_WriteToDataQueue(SDL_DataQueue *queue, const void *_data, const size_t _len)
SDL_assert(!packet || (packet->datalen <= packet_size));
if (!packet || (packet->datalen >= packet_size)) {
/* tail packet missing or completely full; we need a new packet. */
packet = queue->pool;
if (packet != NULL) {
/* we have one available in the pool. */
queue->pool = packet->next;
} else {
/* Have to allocate a new one! */
packet = (SDL_DataQueuePacket *) SDL_malloc(sizeof (SDL_DataQueuePacket) + packet_size);
if (packet == NULL) {
/* uhoh, reset so we've queued nothing new, free what we can. */
if (!origtail) {
packet = queue->head; /* whole queue. */
} else {
packet = origtail->next; /* what we added to existing queue. */
origtail->next = NULL;
origtail->datalen = origlen;
}
queue->head = orighead;
queue->tail = origtail;
queue->pool = NULL;
SDL_FreeDataQueueList(packet); /* give back what we can. */
return SDL_OutOfMemory();
packet = AllocateDataQueuePacket(queue);
if (!packet) {
/* uhoh, reset so we've queued nothing new, free what we can. */
if (!origtail) {
packet = queue->head; /* whole queue. */
} else {
packet = origtail->next; /* what we added to existing queue. */
origtail->next = NULL;
origtail->datalen = origlen;
}
queue->head = orighead;
queue->tail = origtail;
queue->pool = NULL;
SDL_FreeDataQueueList(packet); /* give back what we can. */
return SDL_OutOfMemory();
}
packet->datalen = 0;
packet->startpos = 0;
packet->next = NULL;
SDL_assert((queue->head != NULL) == (queue->queued_bytes != 0));
if (queue->tail == NULL) {
queue->head = packet;
} else {
queue->tail->next = packet;
}
queue->tail = packet;
}
datalen = SDL_min(len, packet_size - packet->datalen);
@ -256,5 +271,44 @@ SDL_CountDataQueue(SDL_DataQueue *queue)
return queue ? queue->queued_bytes : 0;
}
void *
SDL_ReserveSpaceInDataQueue(SDL_DataQueue *queue, const size_t len)
{
SDL_DataQueuePacket *packet;
if (!queue) {
SDL_InvalidParamError("queue");
return NULL;
} else if (len == 0) {
SDL_InvalidParamError("len");
return NULL;
} else if (len > queue->packet_size) {
SDL_SetError("len is larger than packet size");
return NULL;
}
packet = queue->head;
if (packet) {
const size_t avail = queue->packet_size - packet->datalen;
if (len <= avail) { /* we can use the space at end of this packet. */
void *retval = packet->data + packet->datalen;
packet->datalen += len;
queue->queued_bytes += len;
return retval;
}
}
/* Need a fresh packet. */
packet = AllocateDataQueuePacket(queue);
if (!packet) {
SDL_OutOfMemory();
return NULL;
}
packet->datalen = len;
queue->queued_bytes += len;
return packet->data;
}
/* vi: set ts=4 sw=4 expandtab: */