improve memory pool

1. fix memory leak:
`memset(&pool_p, 0, sizeof(pool_p))` sets the pointer to NULL,
so `free(pool_p)` does nothing.
2. improve performance by move some code to the outside of the lock.

src/util/src/tmempool.c

@@ -64,6 +64,7 @@ mpool_h taosMemPoolInit(int numOfBlock, int blockSize) {
 
   pthread_mutex_init(&(pool_p->mutex), NULL);
 
+  memset(pool_p->pool, 0, (size_t)(blockSize * numOfBlock));
   for (i = 0; i < pool_p->numOfBlock; ++i) pool_p->freeList[i] = i;
 
   pool_p->first = 0;
@@ -78,9 +79,7 @@ char *taosMemPoolMalloc(mpool_h handle) {
 
   pthread_mutex_lock(&(pool_p->mutex));
 
-  if (pool_p->numOfFree <= 0) {
-    pTrace("mempool: out of memory");
-  } else {
+  if (pool_p->numOfFree > 0) {
     pos = pool_p->pool + pool_p->blockSize * (pool_p->freeList[pool_p->first]);
     pool_p->first++;
     pool_p->first = pool_p->first % pool_p->numOfBlock;
@@ -88,7 +87,8 @@ char *taosMemPoolMalloc(mpool_h handle) {
   }
 
   pthread_mutex_unlock(&(pool_p->mutex));
-  if (pos != NULL) memset(pos, 0, (size_t)pool_p->blockSize);
+
+  if (pos == NULL) pTrace("mempool: out of memory");
   return pos;
 }
 
@@ -98,24 +98,25 @@ void taosMemPoolFree(mpool_h handle, char *pMem) {
 
   if (pMem == NULL) return;
 
-  pthread_mutex_lock(&pool_p->mutex);
-
   index = (int)(pMem - pool_p->pool) % pool_p->blockSize;
-
   if (index != 0) {
     pError("invalid free address:%p\n", pMem);
-  } else {
-    index = (int)((pMem - pool_p->pool) / pool_p->blockSize);
-
-    if (index < 0 || index >= pool_p->numOfBlock) {
-      pError("mempool: error, invalid address:%p\n", pMem);
-    } else {
-      pool_p->freeList[(pool_p->first + pool_p->numOfFree) % pool_p->numOfBlock] = index;
-      pool_p->numOfFree++;
-      memset(pMem, 0, (size_t)pool_p->blockSize);
-    }
+    return;
   }
 
+  index = (int)((pMem - pool_p->pool) / pool_p->blockSize);
+  if (index < 0 || index >= pool_p->numOfBlock) {
+    pError("mempool: error, invalid address:%p\n", pMem);
+    return;
+  }
+
+  memset(pMem, 0, (size_t)pool_p->blockSize);
+
+  pthread_mutex_lock(&pool_p->mutex);
+
+  pool_p->freeList[(pool_p->first + pool_p->numOfFree) % pool_p->numOfBlock] = index;
+  pool_p->numOfFree++;
+
   pthread_mutex_unlock(&pool_p->mutex);
 }
 
@@ -125,6 +126,6 @@ void taosMemPoolCleanUp(mpool_h handle) {
   pthread_mutex_destroy(&pool_p->mutex);
   if (pool_p->pool) free(pool_p->pool);
   if (pool_p->freeList) free(pool_p->freeList);
-  memset(&pool_p, 0, sizeof(pool_p));
+  memset(pool_p, 0, sizeof(*pool_p));
   free(pool_p);
 }