Fix apc_sma_get_avail_size() to look for a contiguous block of memory

apc_sma_get_avail_size() is used by apc_cache_default_expunge() to check
if enough memory is available to store the next cache entry. Therefore,
it is not enough to check the total amount of available memory. The
memory must be available in one contiguous block.

Author: madmajestro

apc_sma.c

@@ -629,13 +629,37 @@ PHP_APCU_API size_t apc_sma_get_avail_mem(apc_sma_t* sma) {
 
 PHP_APCU_API zend_bool apc_sma_get_avail_size(apc_sma_t* sma, size_t size) {
 	int32_t i;
+	sma_header_t* header;
+	void *shmaddr;
+	block_t *cur, *prv;
 
 	for (i = 0; i < sma->num; i++) {
-		sma_header_t* header = SMA_HDR(sma, i);
-		if (header->avail > size) {
-			return 1;
+		header = SMA_HDR(sma, i);
+
+		/* If total size of available memory is too small, we can skip the contiguous-block check */
+		if (header->avail < size) {
+			continue;
+		}
+
+		SMA_LOCK(sma, i);
+		shmaddr = header;
+		prv = BLOCKAT(ALIGNWORD(sizeof(sma_header_t)));
+
+		/* Look for a contiguous block of memory */
+		while (prv->fnext) {
+			cur = BLOCKAT(prv->fnext);
+
+			if (cur->size >= size) {
+				SMA_UNLOCK(sma, i);
+				return 1;
+			}
+
+			prv = cur;
 		}
+
+		SMA_UNLOCK(sma, i);
 	}
+
 	return 0;
 }