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Fix memory leaks in PL/Python.

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Previously, plpython was in the habit of allocating a lot of stuff in
TopMemoryContext, and it was very slipshod about making sure that stuff
got cleaned up; in particular, use of TopMemoryContext as fn_mcxt for
function calls represents an unfixable leak, since we generally don't
know what the called function might have allocated in fn_mcxt.  This
results in session-lifespan leakage in certain usage scenarios, as for
example in a case reported by Ed Behn back in July.

To fix, get rid of all the retail allocations in TopMemoryContext.
All long-lived allocations are now made in sub-contexts that are
associated with specific objects (either pl/python procedures, or
Python-visible objects such as cursors and plans).  We can clean these
up when the associated object is deleted.

I went so far as to get rid of PLy_malloc completely.  There were a
couple of places where it could still have been used safely, but on
the whole it was just an invitation to bad coding.

Haribabu Kommi, based on a draft patch by Heikki Linnakangas;
some further work by me
This commit is contained in:
Tom Lane
2015-11-05 13:52:30 -05:00
parent 64b2e7ad91
commit 8c75ad436f
15 changed files with 222 additions and 224 deletions
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15
src/pl/plpython/plpy_subxactobject.c
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@ -8,6 +8,7 @@
#include "access/xact.h"
#include "executor/spi.h"
#include "utils/memutils.h"
#include "plpython.h"
@ -132,16 +133,22 @@ PLy_subtransaction_enter(PyObject *self, PyObject *unused)
subxact->started = true;
oldcontext = CurrentMemoryContext;
subxactdata = PLy_malloc(sizeof(*subxactdata));
subxactdata = (PLySubtransactionData *)
MemoryContextAlloc(TopTransactionContext,
sizeof(PLySubtransactionData));
subxactdata->oldcontext = oldcontext;
subxactdata->oldowner = CurrentResourceOwner;
BeginInternalSubTransaction(NULL);
/* Do not want to leave the previous memory context */
MemoryContextSwitchTo(oldcontext);
/* Be sure that cells of explicit_subtransactions list are long-lived */
MemoryContextSwitchTo(TopTransactionContext);
explicit_subtransactions = lcons(subxactdata, explicit_subtransactions);
/* Caller wants to stay in original memory context */
MemoryContextSwitchTo(oldcontext);
Py_INCREF(self);
return self;
}
@ -204,7 +211,7 @@ PLy_subtransaction_exit(PyObject *self, PyObject *args)
MemoryContextSwitchTo(subxactdata->oldcontext);
CurrentResourceOwner = subxactdata->oldowner;
PLy_free(subxactdata);
pfree(subxactdata);
/*
* AtEOSubXact_SPI() should not have popped any SPI context, but just in