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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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address Victor's review
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@picnixz
picnixz committed Jan 7, 2025
commit 40d56f1d376b279bc7f14af6ebdf5c6113b660a5
5 changes: 3 additions & 2 deletions Doc/whatsnew/3.14.rst
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Expand Up @@ -621,8 +621,9 @@ Two new events are added: :monitoring-event:`BRANCH_LEFT` and
time
----

* Ensure that :func:`time.sleep(0) <time.sleep>` does not degrade over time
on non-Windows platforms.
* Ensure that the duration of :func:`time.sleep(0) <time.sleep>` is as small
as possible on non-Windows platforms when :manpage:`clock_nanosleep(2)`
or :manpage:`nanosleep(2)` are used to implement :func:`!time.sleep`.
(Contributed by Bénédikt Tran in :gh:`125997`.)


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11 changes: 5 additions & 6 deletions Modules/timemodule.c
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Expand Up @@ -2222,8 +2222,7 @@ pysleep(PyTime_t timeout)
#else
PyTime_t timeout_100ns = _PyTime_As100Nanoseconds(timeout,
_PyTime_ROUND_CEILING);
// Maintain Windows Sleep() semantics for time.sleep(0)
if (timeout_100ns == 0) {
if (timeout_100ns == 0) { // gh-125997
return pysleep_zero();
}
#endif
Expand Down Expand Up @@ -2397,9 +2396,9 @@ pysleep(PyTime_t timeout)
//
// Rationale
// ---------
// time.sleep(0) accumulates delays in the generic implementation, but we can
// skip some calls to `PyTime_Monotonic()` and other checks when the timeout
// is zero. For details, see https://github.com/python/cpython/pull/128274.
// time.sleep(0) is slower when using the generic implementation, but we make
// it faster than time.sleep(eps) for eps > 0 so to avoid some performance
// annoyance. For details, see https://github.com/python/cpython/pull/128274.
static int
pysleep_zero(void)
{
Expand Down Expand Up @@ -2442,7 +2441,7 @@ pysleep_zero(void)
if (PyErr_CheckSignals()) {
return -1;
}
#else
#else // Windows implementation
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
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