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gh-125997: ensure that time.sleep(0) is not delayed on non-Windows platforms #128274

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gh-125997: ensure that time.sleep(0) is not delayed on non-Windows platforms #128274

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3754e9e
Ensure that `time.sleep(0)` does not accumulate delays.
picnixz Dec 26, 2024
3c0c4e6
update globals
picnixz Dec 26, 2024
c18f15f
blurb
picnixz Dec 26, 2024
8d270f2
fix Windows compilation
picnixz Dec 26, 2024
2996937
use a fresh `timeval` variable for select(2) portability
picnixz Dec 27, 2024
80de853
ensure that `errno=0` when calling `pysleep[zero_posix]`
picnixz Dec 27, 2024
c7aa428
removing `assert(errno == 0)`
picnixz Dec 27, 2024
f15436e
add errors assertions
picnixz Dec 27, 2024
68e2988
simplify code
picnixz Dec 29, 2024
afc6186
add comments for `time.sleep(0)`
picnixz Dec 30, 2024
f6a817f
improve time.sleep() tests
picnixz Dec 30, 2024
fb9eb41
update `os` scheduling policy docs
picnixz Dec 30, 2024
ecb9636
update docs
picnixz Dec 30, 2024
1ed9877
add What's New
picnixz Dec 30, 2024
23b4740
fix typo
picnixz Jan 2, 2025
40155ff
optimize `time.sleep(0)` path
picnixz Jan 3, 2025
153b326
update docs
picnixz Jan 3, 2025
7e351c9
update tests
picnixz Jan 3, 2025
285c54a
revert un-necessary docs updates
picnixz Jan 3, 2025
434da31
remove performance tests
picnixz Jan 6, 2025
ff06516
implement platform compile-time dependent `time.sleep(0)`
picnixz Jan 6, 2025
40d56f1
address Victor's review
picnixz Jan 7, 2025
c4ce9cc
update blurb
picnixz Jan 7, 2025
54b6dde
simplify `pysleep`
picnixz Jan 7, 2025
405e473
add newline for readability
picnixz Jan 7, 2025
b803045
revert to a `select()` alternative
picnixz Jan 7, 2025
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implement platform compile-time dependent time.sleep(0) 
The implementations of `time.sleep(0)` on Windows and POSIX are
now handled by the same function. Previously, `time.sleep(0)` on
Windows was handled by `pysleep()` while on POSIX platforms, it
was handled by `pysleep_zero_posix()`.
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@picnixz
picnixz committed Jan 6, 2025
commit ff06516bfef7484795c28da777eedf596efc7724
43 changes: 20 additions & 23 deletions Modules/timemodule.c
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Original file line number Diff line number Diff line change
Expand Up @@ -72,9 +72,7 @@ module time

/* Forward declarations */
static int pysleep(PyTime_t timeout);
#ifndef MS_WINDOWS
static int pysleep_zero_posix(void); // see gh-125997
#endif
static int pysleep_zero(void); // see gh-125997


typedef struct {
Expand Down Expand Up @@ -2219,7 +2217,14 @@ pysleep(PyTime_t timeout)
assert(!PyErr_Occurred());
#ifndef MS_WINDOWS
if (timeout == 0) { // gh-125997
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return pysleep_zero_posix();
return pysleep_zero();
}
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#else
PyTime_t timeout_100ns = _PyTime_As100Nanoseconds(timeout,
_PyTime_ROUND_CEILING);
// Maintain Windows Sleep() semantics for time.sleep(0)
if (timeout_100ns == 0) {
return pysleep_zero();
}
#endif

Expand Down Expand Up @@ -2300,21 +2305,6 @@ pysleep(PyTime_t timeout)

return 0;
#else // MS_WINDOWS
PyTime_t timeout_100ns = _PyTime_As100Nanoseconds(timeout,
_PyTime_ROUND_CEILING);

// Maintain Windows Sleep() semantics for time.sleep(0)
if (timeout_100ns == 0) {
Py_BEGIN_ALLOW_THREADS
// A value of zero causes the thread to relinquish the remainder of its
// time slice to any other thread that is ready to run. If there are no
// other threads ready to run, the function returns immediately, and
// the thread continues execution.
Sleep(0);
Py_END_ALLOW_THREADS
return 0;
}

LARGE_INTEGER relative_timeout;
// No need to check for integer overflow, both types are signed
assert(sizeof(relative_timeout) == sizeof(timeout_100ns));
Expand Down Expand Up @@ -2401,7 +2391,6 @@ pysleep(PyTime_t timeout)
}


#ifndef MS_WINDOWS
// time.sleep(0) optimized implementation.
// On error, raise an exception and return -1.
// On success, return 0.
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Expand All @@ -2412,10 +2401,10 @@ pysleep(PyTime_t timeout)
// skip some calls to `PyTime_Monotonic()` and other checks when the timeout
// is zero. For details, see https://github.com/python/cpython/pull/128274.
static int
pysleep_zero_posix(void)
pysleep_zero(void)
{
assert(!PyErr_Occurred());

#ifndef MS_WINDOWS
int ret, err;
Py_BEGIN_ALLOW_THREADS
#ifdef HAVE_CLOCK_NANOSLEEP
Expand Down Expand Up @@ -2453,6 +2442,14 @@ pysleep_zero_posix(void)
if (PyErr_CheckSignals()) {
return -1;
}
#else
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Outdated
Py_BEGIN_ALLOW_THREADS
// A value of zero causes the thread to relinquish the remainder of its
// time slice to any other thread that is ready to run. If there are no
// other threads ready to run, the function returns immediately, and
// the thread continues execution.
Sleep(0);
Py_END_ALLOW_THREADS
#endif
return 0;
}
#endif