出于好奇，我想知道我的程序有多少次被操作系统上下文切换。就像所有的寄存器都被保存了，控制权被传递给了另一个进程或线程，然后过了一段时间一切都恢复了，我们继续，因为它从未发生过。
系统是否在某处维护了这样一个数字，或者是否存在某种黑客攻击或其他什么？
我特别关注 Linux，但我也对其他系统感兴趣。
【问题讨论】：
标签： parallel-processing context-switch
好吧，让我们来看看这个案例。 Linux 类型的 O/S 系统地保留了这些细节，并且可以使用 python 的舒适性，既可以检查状态，也可以轻松设计监控系统，可以报告任何过度情况（前者非常匹配只是出于好奇的情况，后者对于系统工作的任何返工/重用都非常方便）：
这里的 python 既可以起到教育作用，又可以方便和舒适地进一步扩展功能范围：
分配signal.signal( signal.SIGALRM, SIG_ALRM_handler_A ) 和时间后，系统准备好报告自愿和非自愿（强制）上下文切换，
其中使用了“FAT”阻塞计算，由于历史原因，非 GIL Numpy/C/FORTRAN 代码会受到非自愿 CtxSwitched 情况的干扰，如下所示
(len(str([np.math.factorial(2**f) for f in range(20)][-1])))
但是
主要使用任何其他PID-号码，
这种微不足道的监控机制可以用于任何其他目的：
########################################################################
### SIGALRM_handler_
###
import psutil, resource, os, time
SIG_ALRM_last_ctx_switch_VOLUNTARY = -1
SIG_ALRM_last_ctx_switch_FORCED = -1
def SIG_ALRM_handler_A( aSigNUM, aFrame ): # SIG_ALRM fired evenly even during [ np.math.factorial( 2**f ) for f in range( 20 ) ] C-based processing =======================================
# onEntry_ROTATE_SigHandlers() -- MAY set another sub-sampled SIG_ALRM_handler_B() ... { last: 0, 0: handler_A, 1: handler_B, 2: handler_C }
#
# onEntry_SEQ of calls of regular, hierarchically timed MONITORS ( just the SNAPSHOT-DATA ACQUISITION Code-SPRINTs, handle later due to possible TimeDOMAIN overlaps )
#
#
# print( time.ctime() )
# print( formatExtMemoryUsed( getExtMemoryUsed() ) )
# print( 60 * "=", psutil.Process( os.getpid() ).num_ctx_switches(), "~~~", aProcess.cpu_percent( interval = 0 ) )
# ??? # WHY CPU 0.0%
aProcess = psutil.Process( os.getpid() )
aProcessCpuPCT = aProcess.cpu_percent( interval = 0 ) # EVENLY-TIME-STEPPED
aCtxSwitchNUMs = aProcess.num_ctx_switches() # THIS PROCESS ( may inspect other per-incident later ... on anomaly )
aVolCtxSwitchCNT = aCtxSwitchNUMs.voluntary
aForcedSwitchCNT = aCtxSwitchNUMs.involuntary
global SIG_ALRM_last_ctx_switch_VOLUNTARY
global SIG_ALRM_last_ctx_switch_FORCED
if ( SIG_ALRM_last_ctx_switch_VOLUNTARY != -1 ): # .INIT VALUE STILL UNCHANGED
#----------
# .ON_TICK: must process delta(s)
if ( SIG_ALRM_last_ctx_switch_VOLUNTARY == aVolCtxSwitchCNT ):
#
# AN INDIRECT INDICATION OF A LONG-RUNNING WORKLOAD OUTSIDE GIL-STEPPING ( regex / C-lib / FORTRAN / numpy-block et al )
# ||||| vvv
# SIG_: Wed Oct 19 12:24:32 2016 ------------------------------ pctxsw(voluntary=48714, involuntary=315) ~~~ 0.0
# SIG_: Wed Oct 19 12:24:37 2016 ------------------------------ pctxsw(voluntary=48714, involuntary=323) ~~~ 0.0
# SIG_: Wed Oct 19 12:24:42 2016 ------------------------------ pctxsw(voluntary=48714, involuntary=331) ~~~ 0.0
# SIG_: Wed Oct 19 12:24:47 2016 ------------------------------ pctxsw(voluntary=48714, involuntary=338) ~~~ 0.0
# SIG_: Wed Oct 19 12:24:52 2016 ------------------------------ pctxsw(voluntary=48714, involuntary=346) ~~~ 0.0
# SIG_: Wed Oct 19 12:24:57 2016 ------------------------------ pctxsw(voluntary=48714, involuntary=353) ~~~ 0.0
# ... ||||| ^^^
# 00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000]
# >>> ||||| |||
# vvvvv |||
# SIG_: Wed Oct 19 12:26:17 2016 ------------------------------ pctxsw(voluntary=49983, involuntary=502) ~~~ 0.0
# SIG_: Wed Oct 19 12:26:22 2016 ------------------------------ pctxsw(voluntary=49984, involuntary=502) ~~~ 0.0
# SIG_: Wed Oct 19 12:26:27 2016 ------------------------------ pctxsw(voluntary=49985, involuntary=502) ~~~ 0.0
# SIG_: Wed Oct 19 12:26:32 2016 ------------------------------ pctxsw(voluntary=49986, involuntary=502) ~~~ 0.0
# SIG_: Wed Oct 19 12:26:37 2016 ------------------------------ pctxsw(voluntary=49987, involuntary=502) ~~~ 0.0
# SIG_: Wed Oct 19 12:26:42 2016 ------------------------------ pctxsw(voluntary=49988, involuntary=502) ~~~ 0.0
#rint( "SIG_ALRM_handler_A(): A SUSPECT CPU-LOAD:: ", time.ctime(), 10 * "-", aProcess.num_ctx_switches(), "{0: > 8.2f} CPU_CORE_LOAD [%]".format( aProcessCpuPCT ), " INSPECT processes ... ev. add a StateFull-self-Introspection" )
print( "SIG_ALRM_handler_A(): A SUSPECT CPU-LOAD:: ", time.ctime(), 10 * "-", aProcess.num_ctx_switches(), "{0:_>60s}".format( str( aProcess.threads() ) ), " INSPECT processes ... ev. add a StateFull-self-Introspection" )
#rint( "SIG_ALRM_handler_A(): A SUSPECT CPU-LOAD:: ", str( resource.getrusage( resource.RUSAGE_SELF ) )[22:] )
else:
#----------
# .ON_INIT: may report .INIT()
#rint( "SIG_ALRM_handler_A(): A SUSPECT CPU-LOAD:: ", time.ctime(), ...
print( "SIG_ALRM_handler_A(): activated ", time.ctime(), 30 * "-", aProcess.num_ctx_switches() )
##########
# FINALLY:
SIG_ALRM_last_ctx_switch_VOLUNTARY = aVolCtxSwitchCNT # .STO ACTUALs
SIG_ALRM_last_ctx_switch_FORCED = aForcedSwitchCNT # .STO ACTUALs
#rint( "SIG_: ", time.ctime(), 30 * "-", aProcess.num_ctx_switches(), " ~~~ ", aProcess.cpu_percent( interval = 0 ), " % -?- ", aProcess.threads() )
#____________________________________________________________________
# SIG_ALRM_handler_A( aSigNUM, aFrame ): DEFINED
#####################################################################
##########
# FINALLY:
#
# > signal.signal( signal.SIGALRM, SIG_ALRM_handler_A ) # .ASSOC { SIGALRM: thisHandler }
# > signal.setitimer( signal.ITIMER_REAL, 10, 5 ) # .SET @5 [sec] interval, after first run, starting after 10[sec] initial-delay
# > signal.setitimer( signal.ITIMER_REAL, 0, 5 ) # .UNSET
# > SIG_ALRM_last_ctx_switch_VOLUNTARY = -1 # .RESET .INIT() the global { signalling | state }-variable
# > len(str([np.math.factorial(2**f) for f in range(20)][-1])) # .RUN A "FAT"-BLOCKING CHUNK OF A regex/numpy/C/FORTRAN-calculus
虽然没有对类似的深度进行详细阐述，但上述内容同样适用于：
>>> psutil.Process( 18263 ).cpu_percent() 0.0
>>> psutil.Process( 18263 ).ppid() 18054
>>> psutil.Process( 18054 ).cpu_percent() 0.0
=== ( 18054 ).threads(): [ 17679, 17680, 17681, 18054, 18265, 18266, 18267, ]
==4 -------------vvv-------------------=4--------------vvvv-------------------=4--------------vvv
>>> [ psutil.Process( p ).num_ctx_switches() for p in ( 18259, 18260, 18261 ) ] [pctxsw(voluntary=4, involuntary=267), pctxsw(voluntary=4, involuntary=1909), pctxsw(voluntary=4, involuntary=444)]
>>> [ psutil.Process( p ).num_ctx_switches() for p in ( 18259, 18260, 18261 ) ] [pctxsw(voluntary=4, involuntary=273), pctxsw(voluntary=4, involuntary=1915), pctxsw(voluntary=4, involuntary=445)]
>>> [ psutil.Process( p ).num_ctx_switches() for p in ( 18259, 18260, 18261 ) ] [pctxsw(voluntary=4, involuntary=275), pctxsw(voluntary=4, involuntary=1917), pctxsw(voluntary=4, involuntary=445)]
【讨论】：