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Commit74ed3db

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gh-109649: Add os.process_cpu_count() function
* Refactor os_sched_getaffinity_impl(): move variable definitions to their first assignment.* Fix test_posix.test_sched_getaffinity(): restore the old CPU mask when the test completes!* Doc: Specify that os.cpu_count() counts *logicial* CPUs.* Doc: Specify that os.sched_getaffinity(0) is related to the calling thread.
1 parent2c23419 commit74ed3db

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8 files changed

+124
-47
lines changed

8 files changed

+124
-47
lines changed

‎Doc/library/os.rst

Lines changed: 24 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -5141,8 +5141,12 @@ operating system.
51415141

51425142
..function::sched_getaffinity(pid, /)
51435143

5144-
Return the set of CPUs the process with PID *pid* (or the current process
5145-
if zero) is restricted to.
5144+
Return the set of CPUs the process with PID *pid* is restricted to.
5145+
5146+
If *pid* is zero, return the set of CPUs the calling thread of the current
5147+
process is restricted to.
5148+
5149+
See also the:func:`process_cpu_count` function.
51465150

51475151

51485152
.. _os-path:
@@ -5183,12 +5187,11 @@ Miscellaneous System Information
51835187

51845188
..function::cpu_count()
51855189

5186-
Return the number of CPUs in the system. Returns ``None`` if undetermined.
5187-
5188-
This number is not equivalent to the number of CPUs the current process can
5189-
use. The number of usable CPUs can be obtained with
5190-
``len(os.sched_getaffinity(0))``
5190+
Return the number of logical CPUs in the **system**. Returns ``None`` if
5191+
undetermined.
51915192

5193+
The:func:`process_cpu_count` function can be used to get the number of
5194+
logical CPUs usable by the calling thread of the **current process**.
51925195

51935196
..versionadded::3.4
51945197

@@ -5202,6 +5205,20 @@ Miscellaneous System Information
52025205
..availability::Unix.
52035206

52045207

5208+
..function::process_cpu_count()
5209+
5210+
Get the number of logical CPUs usable by the calling thread of the **current
5211+
process**. Returns ``None`` if undetermined. It can be less than
5212+
:func:`cpu_count` depending on the CPU affinity.
5213+
5214+
The:func:`cpu_count` function can be used to get the number of logical CPUs
5215+
in the **system**.
5216+
5217+
See also the:func:`sched_getaffinity` functions.
5218+
5219+
..versionadded::3.13
5220+
5221+
52055222
..function::sysconf(name, /)
52065223

52075224
Return integer-valued system configuration values. If the configuration value

‎Doc/whatsnew/3.13.rst

Lines changed: 7 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -163,6 +163,13 @@ opcode
163163
documented or exposed through ``dis``, and were not intended to be
164164
used externally.
165165

166+
os
167+
--
168+
169+
* Add:func:`os.process_cpu_count` function to get the number of logical CPUs
170+
usable by the calling thread of the current process.
171+
(Contributed by Victor Stinner in:gh:`109649`.)
172+
166173
pathlib
167174
-------
168175

‎Lib/os.py

Lines changed: 13 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1136,3 +1136,16 @@ def add_dll_directory(path):
11361136
cookie,
11371137
nt._remove_dll_directory
11381138
)
1139+
1140+
1141+
if_exists('sched_getaffinity'):
1142+
defprocess_cpu_count():
1143+
"""
1144+
Get the number of logical CPUs usable by the current process.
1145+
1146+
Return None if indeterminable.
1147+
"""
1148+
returnlen(sched_getaffinity(0))
1149+
else:
1150+
# Just an alias to cpu_count() (same docstring)
1151+
process_cpu_count=cpu_count

‎Lib/test/test_os.py

Lines changed: 32 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -3996,14 +3996,42 @@ def test_oserror_filename(self):
39963996
self.fail(f"No exception thrown by{func}")
39973997

39983998
classCPUCountTests(unittest.TestCase):
3999+
defcheck_cpu_count(self,cpus):
4000+
ifcpusisNone:
4001+
self.skipTest("Could not determine the number of CPUs")
4002+
4003+
self.assertIsInstance(cpus,int)
4004+
self.assertGreater(cpus,0)
4005+
39994006
deftest_cpu_count(self):
40004007
cpus=os.cpu_count()
4001-
ifcpusisnotNone:
4002-
self.assertIsInstance(cpus,int)
4003-
self.assertGreater(cpus,0)
4004-
else:
4008+
self.check_cpu_count(cpus)
4009+
4010+
deftest_process_cpu_count(self):
4011+
cpus=os.process_cpu_count()
4012+
self.assertLessEqual(cpus,os.cpu_count())
4013+
self.check_cpu_count(cpus)
4014+
4015+
@unittest.skipUnless(hasattr(os,'sched_setaffinity'),
4016+
"don't have sched affinity support")
4017+
deftest_process_cpu_count_affinity(self):
4018+
ncpu=os.cpu_count()
4019+
ifncpuisNone:
40054020
self.skipTest("Could not determine the number of CPUs")
40064021

4022+
# Disable one CPU
4023+
mask=os.sched_getaffinity(0)
4024+
iflen(mask)<=1:
4025+
self.skipTest(f"sched_getaffinity() returns less than "
4026+
f"2 CPUs:{sorted(mask)}")
4027+
self.addCleanup(os.sched_setaffinity,0,list(mask))
4028+
mask.pop()
4029+
os.sched_setaffinity(0,mask)
4030+
4031+
# test process_cpu_count()
4032+
affinity=os.process_cpu_count()
4033+
self.assertEqual(affinity,ncpu-1)
4034+
40074035

40084036
# FD inheritance check is only useful for systems with process support.
40094037
@support.requires_subprocess()

‎Lib/test/test_posix.py

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1205,6 +1205,7 @@ def test_sched_getaffinity(self):
12051205
@requires_sched_affinity
12061206
deftest_sched_setaffinity(self):
12071207
mask=posix.sched_getaffinity(0)
1208+
self.addCleanup(posix.sched_setaffinity,0,list(mask))
12081209
iflen(mask)>1:
12091210
# Empty masks are forbidden
12101211
mask.pop()
Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,2 @@
1+
Add:func:`os.process_cpu_count` function to get the number of logical CPUs
2+
usable by the calling thread of the current process. Patch by Victor Stinner.

‎Modules/clinic/posixmodule.c.h

Lines changed: 3 additions & 5 deletions
Some generated files are not rendered by default. Learn more aboutcustomizing how changed files appear on GitHub.

‎Modules/posixmodule.c

Lines changed: 42 additions & 31 deletions
Original file line numberDiff line numberDiff line change
@@ -8133,39 +8133,45 @@ static PyObject *
81338133
os_sched_getaffinity_impl(PyObject*module,pid_tpid)
81348134
/*[clinic end generated code: output=f726f2c193c17a4f input=983ce7cb4a565980]*/
81358135
{
8136-
intcpu,ncpus,count;
8136+
intncpus=NCPUS_START;
81378137
size_tsetsize;
8138-
cpu_set_t*mask=NULL;
8139-
PyObject*res=NULL;
8138+
cpu_set_t*mask;
81408139

8141-
ncpus=NCPUS_START;
81428140
while (1) {
81438141
setsize=CPU_ALLOC_SIZE(ncpus);
81448142
mask=CPU_ALLOC(ncpus);
8145-
if (mask==NULL)
8143+
if (mask==NULL) {
81468144
returnPyErr_NoMemory();
8147-
if (sched_getaffinity(pid,setsize,mask)==0)
8145+
}
8146+
if (sched_getaffinity(pid,setsize,mask)==0) {
81488147
break;
8148+
}
81498149
CPU_FREE(mask);
8150-
if (errno!=EINVAL)
8150+
if (errno!=EINVAL) {
81518151
returnposix_error();
8152+
}
81528153
if (ncpus>INT_MAX /2) {
8153-
PyErr_SetString(PyExc_OverflowError,"could not allocate "
8154-
"a large enough CPU set");
8154+
PyErr_SetString(PyExc_OverflowError,
8155+
"could not allocatea large enough CPU set");
81558156
returnNULL;
81568157
}
8157-
ncpus=ncpus*2;
8158+
ncpus*=2;
81588159
}
81598160

8160-
res=PySet_New(NULL);
8161-
if (res==NULL)
8161+
PyObject*res=PySet_New(NULL);
8162+
if (res==NULL) {
81628163
gotoerror;
8163-
for (cpu=0,count=CPU_COUNT_S(setsize,mask);count;cpu++) {
8164+
}
8165+
8166+
intcpu=0;
8167+
intcount=CPU_COUNT_S(setsize,mask);
8168+
for (;count;cpu++) {
81648169
if (CPU_ISSET_S(cpu,setsize,mask)) {
81658170
PyObject*cpu_num=PyLong_FromLong(cpu);
81668171
--count;
8167-
if (cpu_num==NULL)
8172+
if (cpu_num==NULL) {
81688173
gotoerror;
8174+
}
81698175
if (PySet_Add(res,cpu_num)) {
81708176
Py_DECREF(cpu_num);
81718177
gotoerror;
@@ -8177,12 +8183,12 @@ os_sched_getaffinity_impl(PyObject *module, pid_t pid)
81778183
returnres;
81788184

81798185
error:
8180-
if (mask)
8186+
if (mask) {
81818187
CPU_FREE(mask);
8188+
}
81828189
Py_XDECREF(res);
81838190
returnNULL;
81848191
}
8185-
81868192
#endif/* HAVE_SCHED_SETAFFINITY */
81878193

81888194
#endif/* HAVE_SCHED_H */
@@ -14333,44 +14339,49 @@ os_get_terminal_size_impl(PyObject *module, int fd)
1433314339
/*[clinic input]
1433414340
os.cpu_count
1433514341
14336-
Return the number of CPUs in the system; return None if indeterminable.
14342+
Return the number oflogicalCPUs in the system.
1433714343
14338-
This number is not equivalent to the number of CPUs the current process can
14339-
use. The number of usable CPUs can be obtained with
14340-
``len(os.sched_getaffinity(0))``
14344+
Return None if indeterminable.
1434114345
[clinic start generated code]*/
1434214346

1434314347
staticPyObject*
1434414348
os_cpu_count_impl(PyObject*module)
14345-
/*[clinic end generated code: output=5fc29463c3936a9c input=e7c8f4ba6dbbadd3]*/
14349+
/*[clinic end generated code: output=5fc29463c3936a9c input=ba2f6f8980a0e2eb]*/
1434614350
{
14347-
intncpu=0;
14351+
intncpu;
1434814352
#ifdefMS_WINDOWS
14349-
#ifdefMS_WINDOWS_DESKTOP
14353+
#ifdefMS_WINDOWS_DESKTOP
1435014354
ncpu=GetActiveProcessorCount(ALL_PROCESSOR_GROUPS);
14351-
#endif
14355+
# else
14356+
ncpu=0;
14357+
# endif
14358+
1435214359
#elif defined(__hpux)
1435314360
ncpu=mpctl(MPC_GETNUMSPUS,NULL,NULL);
14361+
1435414362
#elif defined(HAVE_SYSCONF)&& defined(_SC_NPROCESSORS_ONLN)
1435514363
ncpu=sysconf(_SC_NPROCESSORS_ONLN);
14364+
1435614365
#elif defined(__VXWORKS__)
1435714366
ncpu=_Py_popcount32(vxCpuEnabledGet());
14367+
1435814368
#elif defined(__DragonFly__)|| \
1435914369
defined(__OpenBSD__)|| \
1436014370
defined(__FreeBSD__)|| \
1436114371
defined(__NetBSD__)|| \
1436214372
defined(__APPLE__)
14363-
intmib[2];
14373+
ncpu=0;
1436414374
size_tlen=sizeof(ncpu);
14365-
mib[0]=CTL_HW;
14366-
mib[1]=HW_NCPU;
14367-
if (sysctl(mib,2,&ncpu,&len,NULL,0)!=0)
14375+
intmib[2]= {CTL_HW,HW_NCPU};
14376+
if (sysctl(mib,2,&ncpu,&len,NULL,0)!=0) {
1436814377
ncpu=0;
14378+
}
1436914379
#endif
14370-
if (ncpu >=1)
14371-
returnPyLong_FromLong(ncpu);
14372-
else
14380+
14381+
if (ncpu<1) {
1437314382
Py_RETURN_NONE;
14383+
}
14384+
returnPyLong_FromLong(ncpu);
1437414385
}
1437514386

1437614387

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