Use a freelist to speed-up block allocation and deallocation in collections.deque().

diff --git a/Modules/_collectionsmodule.c b/Modules/_collectionsmodule.c
index ca24be7300f70fbfb400c6b44553f7c8d7904c03..e5c32182124eb810330f16409fccbb5967b4b2cd 100644 (file)
--- a/Modules/_collectionsmodule.c
+++ b/Modules/_collectionsmodule.c
@@ -51,6 +51,10 @@ typedef struct BLOCK {
        PyObject *data[BLOCKLEN];
 } block;
 
+#define MAXFREEBLOCKS 10
+static int numfreeblocks = 0;
+static block *freeblocks[MAXFREEBLOCKS];
+
 static block *
 newblock(block *leftlink, block *rightlink, int len) {
        block *b;
@@ -66,16 +70,32 @@ newblock(block *leftlink, block *rightlink, int len) {
                                "cannot add more blocks to the deque");
                return NULL;
        }
-       b = PyMem_Malloc(sizeof(block));
-       if (b == NULL) {
-               PyErr_NoMemory();
-               return NULL;
+       if (numfreeblocks) {
+               numfreeblocks -= 1;
+               b = freeblocks[numfreeblocks];
+       } else {
+               b = PyMem_Malloc(sizeof(block));
+               if (b == NULL) {
+                       PyErr_NoMemory();
+                       return NULL;
+               }
        }
        b->leftlink = leftlink;
        b->rightlink = rightlink;
        return b;
 }
 
+void
+freeblock(block *b)
+{
+       if (numfreeblocks < MAXFREEBLOCKS) {
+               freeblocks[numfreeblocks] = b;
+               numfreeblocks++;
+       } else {
+               PyMem_Free(b);
+       }
+}
+
 typedef struct {
        PyObject_HEAD
        block *leftblock;
@@ -161,7 +181,7 @@ deque_pop(dequeobject *deque, PyObject *unused)
                } else {
                        prevblock = deque->rightblock->leftlink;
                        assert(deque->leftblock != deque->rightblock);
-                       PyMem_Free(deque->rightblock);
+                       freeblock(deque->rightblock);
                        prevblock->rightlink = NULL;
                        deque->rightblock = prevblock;
                        deque->rightindex = BLOCKLEN - 1;
@@ -198,7 +218,7 @@ deque_popleft(dequeobject *deque, PyObject *unused)
                } else {
                        assert(deque->leftblock != deque->rightblock);
                        prevblock = deque->leftblock->rightlink;
-                       PyMem_Free(deque->leftblock);
+                       freeblock(deque->leftblock);
                        assert(prevblock != NULL);
                        prevblock->leftlink = NULL;
                        deque->leftblock = prevblock;
@@ -559,7 +579,7 @@ deque_dealloc(dequeobject *deque)
        if (deque->leftblock != NULL) {
                deque_clear(deque);
                assert(deque->leftblock != NULL);
-               PyMem_Free(deque->leftblock);
+               freeblock(deque->leftblock);
        }
        deque->leftblock = NULL;
        deque->rightblock = NULL;