8000 bpo-28254: Add a C-API for controlling the state of the garbage collector by scoder · Pull Request #25687 · python/cpython · GitHub
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bpo-28254: Add a C-API for controlling the state of the garbage collector #25687

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merged 17 commits into from
Apr 28, 2021
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bpo-28254: Return the previous GC state from the Enable/Disable funct…
…ions to make it easy for users to ('atomically') know whether they actually changed something and what state to go back to later. Also, returning an "int" may make it easier to add error handling later, if that becomes needed at some point.
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scoder committed Apr 28, 2021
commit 56465a9c1b8ab8b5c4d0b203abd0881db9187aff
4 changes: 2 additions & 2 deletions Include/objimpl.h
Original file line number Diff line number Diff line change
Expand Up @@ -153,8 +153,8 @@ PyAPI_FUNC(PyVarObject *) _PyObject_NewVar(PyTypeObject *, Py_ssize_t);
/* C equivalent of gc.collect() which ignores the state of gc.enabled. */
PyAPI_FUNC(Py_ssize_t) PyGC_Collect(void);
/* C API for controlling the state of the garbage collector */
PyAPI_FUNC(void) PyGC_Enable(void);
PyAPI_FUNC(void) PyGC_Disable(void);
PyAPI_FUNC(int) PyGC_Enable(void);
PyAPI_FUNC(int) PyGC_Disable(void);
PyAPI_FUNC(int) PyGC_IsEnabled(void);

/* Test if a type has a GC head */
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27 changes: 19 additions & 8 deletions Modules/_testcapimodule.c
Original file line number Diff line number Diff line change
Expand Up @@ -149,20 +149,31 @@ test_gc_control(PyObject *self, PyObject *Py_UNUSED(ignored))
{
int orig_enabled = PyGC_IsEnabled();
const char* msg = "ok";
int old_state;

PyGC_Enable();
msg = "enable(1)";
old_state = PyGC_Enable();
msg = "Enable(1)";
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Bugs are unlikely. IMO using assert() is good enough for _testcapi tests. You can leave the code as it is ;-)

See for example test_refcount_funcs() which uses assert().

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I was thinking that assertions can be compiled out, which is decidedly not intended here.

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In general yes, but _testcapimodule.c starts with:

/* Always enable assertions */
#undef NDEBUG

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Good to know! I'd keep the test as it is though. It doesn't really hurt, I think.

if (old_state != orig_enabled) goto failed;
msg = "IsEnabled(1)";
if (!PyGC_IsEnabled()) goto failed;
PyGC_Disable();
msg = "disable(1)";

old_state = PyGC_Disable();
msg = "disable(2)";
if (!old_state) goto failed;
msg = "IsEnabled(2)";
if (PyGC_IsEnabled()) goto failed;
PyGC_Enable();
msg = "enable(2)";

old_state = PyGC_Enable();
msg = "enable(3)";
if (old_state) goto failed;
msg = "IsEnabled(3)";
if (!PyGC_IsEnabled()) goto failed;

if (!orig_enabled) {
PyGC_Disable();
msg = "disable(2)";
old_state = PyGC_Disable();
msg = "disable(4)";
if (old_state) goto failed;
msg = "IsEnabled(4)";
if (PyGC_IsEnabled()) goto failed;
}

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8 changes: 6 additions & 2 deletions Modules/gcmodule.c
Original file line number Diff line number Diff line change
Expand Up @@ -2079,18 +2079,22 @@ PyGC_Collect(void)
}

/* C API for controlling the state of the garbage collector */
void
int
PyGC_Enable(void)
{
GCState *gcstate = get_gc_state();
int old_state = gcstate->enabled;
gcstate->enabled = 1;
return old_state;
}

void
int
PyGC_Disable(void)
{
GCState *gcstate = get_gc_state();
int old_state = gcstate->enabled;
gcstate->enabled = 0;
return old_state;
}

int
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0