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Modules: implement zig-zag scanning in autoMemoryFreed().

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Most of the time to check the last element is the way to go, however
there are patterns where the contrary is the best choice. Zig-zag
scanning implemented in this commmit always checks the obvious element
first (the last added -- think at a loop where the last element
allocated gets freed again and again), and continues checking one
element in the head and one in the tail.

Thanks to @dvisrky that fixed the original implementation of the
function and proposed zig zag scanning.
This commit is contained in:
antirez 2016-06-23 09:09:51 +02:00
parent 2fe9b79897
commit f2dbc02f65
1 changed files with 20 additions and 16 deletions
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34
src/module.c
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@ -610,23 +610,27 @@ void autoMemoryAdd(RedisModuleCtx *ctx, int type, void *ptr) {
void autoMemoryFreed(RedisModuleCtx *ctx, int type, void *ptr) { void autoMemoryFreed(RedisModuleCtx *ctx, int type, void *ptr) {
if (!(ctx->flags & REDISMODULE_CTX_AUTO_MEMORY)) return; if (!(ctx->flags & REDISMODULE_CTX_AUTO_MEMORY)) return;
int j; int count = (ctx->amqueue_used+1)/2;
for (j = ctx->amqueue_used - 1; j >= 0; j--) { for (int j = 0; j < count; j++) {
if (ctx->amqueue[j].type == type && for (int side = 0; side < 2; side++) {
ctx->amqueue[j].ptr == ptr) /* For side = 0 check right side of the array, for
{ * side = 1 check the left side instead (zig-zag scanning). */
ctx->amqueue[j].type = REDISMODULE_AM_FREED; int i = (side == 0) ? (ctx->amqueue_used - 1 - j) : j;
if (ctx->amqueue[i].type == type &&
ctx->amqueue[i].ptr == ptr)
{
ctx->amqueue[i].type = REDISMODULE_AM_FREED;
/* Switch the freed element and the top element, to avoid growing /* Switch the freed element and the top element, to avoid growing
* the queue unnecessarily if we allocate/free in a loop */ * the queue unnecessarily if we allocate/free in a loop */
if (j != ctx->amqueue_used-1) { if (i != ctx->amqueue_used-1) {
ctx->amqueue[j] = ctx->amqueue[ctx->amqueue_used-1]; ctx->amqueue[i] = ctx->amqueue[ctx->amqueue_used-1];
}
/* Reduce the size of the queue because we either moved the top
* element elsewhere or freed it */
ctx->amqueue_used--;
return;
} }
/* Reduce the size of the queue because we either moved the top
* element elsewhere or freed it */
ctx->amqueue_used--;
break;
} }
} }
} }