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bpo-28254: Add a C-API for controlling the state of the garbage collector #25687

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Merged
vstinner merged 17 commits into from
Apr 28, 2021
Merged

bpo-28254: Add a C-API for controlling the state of the garbage collector #25687

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6229a31
bpo-28254: Add a C-API for controlling the state of the garbage colle…
scoder Apr 28, 2021
bfbadb9
bpo-28254: Improve markup and add a What's New entry.
scoder Apr 28, 2021
f41d269
Apply suggestions from code review
pablogsal Apr 28, 2021
56465a9
bpo-28254: Return the previous GC state from the Enable/Disable funct…
scoder Apr 28, 2021
7b6e320
Update Modules/_testcapimodule.c
pablogsal Apr 28, 2021
b7e4ee3
Update Modules/_testcapimodule.c
pablogsal Apr 28, 2021
4e11560
Update Modules/_testcapimodule.c
pablogsal Apr 28, 2021
e5f0077
bpo-28254: Formatting.
scoder Apr 28, 2021
c64aa42
bpo-28254: Move new functions to a better place (not cutting into the…
scoder Apr 28, 2021
cbee918
Remove an incorrect part of a comment: PyGC_Collect() actually does n…
scoder Apr 28, 2021
0f7e608
bpo-28254: Add documentation for the PyGC_*() functions.
scoder Apr 28, 2021
80c3625
bpo-28254: Add new PyGC_*() functions to the stable ABI list.
scoder Apr 28, 2021
25fb2aa
bpo-28254: Apply suggestions from doc review.
scoder Apr 28, 2021
10ad929
Apply suggestions from doc review
scoder Apr 28, 2021
1ffe937
Add a word on how PyGC_Collect() and gc.collect() differ.
scoder Apr 28, 2021
d517665
Fix version marker.
scoder Apr 28, 2021
84fb2af
Fix version marker (II).
scoder 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
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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
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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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@vstinner vstinner Apr 28, 2021

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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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@scoder scoder Apr 28, 2021

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

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@vstinner vstinner Apr 28, 2021

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In general yes, but _testcapimodule.c starts with:

/* Always enable assertions */
#undef NDEBUG

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@scoder scoder Apr 28, 2021

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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;
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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;
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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;
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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
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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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