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Revert "bpo-40521: Remove freelist from collections.deque() (GH-21073)" #24944

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Merged
merged 1 commit into from
Mar 25, 2021
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Revert "bpo-40521: Remove freelist from collections.deque() (GH-21073)" #24944

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23 changes: 21 additions & 2 deletions Modules/_collectionsmodule.c
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Original file line number Diff line number Diff line change
Expand Up @@ -118,9 +118,23 @@ static PyTypeObject deque_type;
#define CHECK_NOT_END(link)
#endif

/* A simple freelisting scheme is used to minimize calls to the memory
allocator. It accommodates common use cases where new blocks are being
added at about the same rate as old blocks are being freed.
*/

#define MAXFREEBLOCKS 16
static Py_ssize_t numfreeblocks = 0;
static block *freeblocks[MAXFREEBLOCKS];
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Can you define the freelist in PyInterpreterState to make it per-interpreter, and so compatible with subinterpreters?

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@rhettinger rhettinger Mar 20, 2021 •
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The subinterpreters PEP is not approved a likely won't be for Python 3.10, so I don't want to pay that cost now. These macros are used heavily throughout the rest of the module and are performance sensitive. For Python 3.11 and later, this can be reapplied. Even then, it would probably be better to remove the freelists entirely than to add fenced logic to get the current interpreter.


static block *
newblock(void) {
block *b = PyMem_Malloc(sizeof(block));
block *b;
if (numfreeblocks) {
numfreeblocks--;
return freeblocks[numfreeblocks];
}
b = PyMem_Malloc(sizeof(block));
if (b != NULL) {
return b;
}
Expand All @@ -131,7 +145,12 @@ newblock(void) {
static void
freeblock(block *b)
{
PyMem_Free(b);
if (numfreeblocks < MAXFREEBLOCKS) {
freeblocks[numfreeblocks] = b;
numfreeblocks++;
} else {
PyMem_Free(b);
}
}

static PyObject *
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