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annotate mercurial/worker.py @ 30422:7bc25549e084

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worker: allow waitforworkers to be non-blocking This patch adds a boolean flag to waitforworkers and makes it non-blocking if set to True. This is to make it possible that we can reap our workers while keep other unrelated children untouched, after receiving SIGCHLD.
author Jun Wu <quark@fb.com>
date Thu, 28 Jul 2016 20:57:07 +0100
parents 47de34f79f93
children 9c25a1a8c685
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
18635
fed06dd07665 worker: count the number of CPUs
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1 # worker.py - master-slave parallelism support
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2 #
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3 # Copyright 2013 Facebook, Inc.
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4 #
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5 # This software may be used and distributed according to the terms of the
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6 # GNU General Public License version 2 or any later version.
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7
25992
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8 from __future__ import absolute_import
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9
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10 import errno
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11 import os
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12 import signal
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13 import sys
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14 import threading
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15
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16 from .i18n import _
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17 from . import (
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18 error,
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19 util,
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20 )
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21
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22 def countcpus():
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23 '''try to count the number of CPUs on the system'''
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24
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25 # posix
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26 try:
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27 n = int(os.sysconf('SC_NPROCESSORS_ONLN'))
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28 if n > 0:
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29 return n
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30 except (AttributeError, ValueError):
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31 pass
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32
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33 # windows
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34 try:
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35 n = int(os.environ['NUMBER_OF_PROCESSORS'])
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36 if n > 0:
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37 return n
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38 except (KeyError, ValueError):
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39 pass
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40
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41 return 1
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42
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43 def _numworkers(ui):
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44 s = ui.config('worker', 'numcpus')
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45 if s:
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46 try:
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47 n = int(s)
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48 if n >= 1:
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49 return n
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50 except ValueError:
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51 raise error.Abort(_('number of cpus must be an integer'))
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52 return min(max(countcpus(), 4), 32)
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53
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54 if os.name == 'posix':
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55 _startupcost = 0.01
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56 else:
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57 _startupcost = 1e30
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58
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59 def worthwhile(ui, costperop, nops):
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60 '''try to determine whether the benefit of multiple processes can
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61 outweigh the cost of starting them'''
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62 linear = costperop * nops
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63 workers = _numworkers(ui)
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64 benefit = linear - (_startupcost * workers + linear / workers)
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65 return benefit >= 0.15
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66
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67 def worker(ui, costperarg, func, staticargs, args):
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68 '''run a function, possibly in parallel in multiple worker
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69 processes.
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70
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71 returns a progress iterator
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72
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73 costperarg - cost of a single task
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74
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75 func - function to run
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76
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77 staticargs - arguments to pass to every invocation of the function
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78
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79 args - arguments to split into chunks, to pass to individual
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80 workers
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81 '''
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82 if worthwhile(ui, costperarg, len(args)):
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83 return _platformworker(ui, func, staticargs, args)
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84 return func(*staticargs + (args,))
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85
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86 def _posixworker(ui, func, staticargs, args):
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87 rfd, wfd = os.pipe()
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88 workers = _numworkers(ui)
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89 oldhandler = signal.getsignal(signal.SIGINT)
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90 signal.signal(signal.SIGINT, signal.SIG_IGN)
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91 pids, problem = [], [0]
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92 def killworkers():
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93 # if one worker bails, there's no good reason to wait for the rest
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94 for p in pids:
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95 try:
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96 os.kill(p, signal.SIGTERM)
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97 except OSError as err:
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98 if err.errno != errno.ESRCH:
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99 raise
30422
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100 def waitforworkers(blocking=True):
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101 for pid in pids:
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102 p, st = os.waitpid(pid, 0 if blocking else os.WNOHANG)
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103 if p:
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104 st = _exitstatus(st)
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105 if st and not problem[0]:
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106 problem[0] = st
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107 killworkers()
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108 for pargs in partition(args, workers):
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109 pid = os.fork()
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110 if pid == 0:
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111 signal.signal(signal.SIGINT, oldhandler)
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112 try:
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113 os.close(rfd)
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114 for i, item in func(*(staticargs + (pargs,))):
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115 os.write(wfd, '%d %s\n' % (i, item))
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116 os._exit(0)
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117 except KeyboardInterrupt:
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118 os._exit(255)
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119 # other exceptions are allowed to propagate, we rely
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120 # on lock.py's pid checks to avoid release callbacks
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121 pids.append(pid)
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122 pids.reverse()
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123 os.close(wfd)
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124 fp = os.fdopen(rfd, 'rb', 0)
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125 t = threading.Thread(target=waitforworkers)
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126 t.start()
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127 def cleanup():
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128 signal.signal(signal.SIGINT, oldhandler)
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129 t.join()
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130 status = problem[0]
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131 if status:
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132 if status < 0:
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133 os.kill(os.getpid(), -status)
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134 sys.exit(status)
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135 try:
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136 for line in util.iterfile(fp):
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137 l = line.split(' ', 1)
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138 yield int(l[0]), l[1][:-1]
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139 except: # re-raises
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140 killworkers()
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141 cleanup()
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142 raise
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143 cleanup()
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144
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145 def _posixexitstatus(code):
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146 '''convert a posix exit status into the same form returned by
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147 os.spawnv
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148
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149 returns None if the process was stopped instead of exiting'''
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150 if os.WIFEXITED(code):
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151 return os.WEXITSTATUS(code)
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152 elif os.WIFSIGNALED(code):
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153 return -os.WTERMSIG(code)
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154
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155 if os.name != 'nt':
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156 _platformworker = _posixworker
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157 _exitstatus = _posixexitstatus
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158
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159 def partition(lst, nslices):
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160 '''partition a list into N slices of roughly equal size
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161
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162 The current strategy takes every Nth element from the input. If
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163 we ever write workers that need to preserve grouping in input
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164 we should consider allowing callers to specify a partition strategy.
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165
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166 mpm is not a fan of this partitioning strategy when files are involved.
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167 In his words:
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168
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169 Single-threaded Mercurial makes a point of creating and visiting
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170 files in a fixed order (alphabetical). When creating files in order,
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171 a typical filesystem is likely to allocate them on nearby regions on
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172 disk. Thus, when revisiting in the same order, locality is maximized
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173 and various forms of OS and disk-level caching and read-ahead get a
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174 chance to work.
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175
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176 This effect can be quite significant on spinning disks. I discovered it
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177 circa Mercurial v0.4 when revlogs were named by hashes of filenames.
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178 Tarring a repo and copying it to another disk effectively randomized
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179 the revlog ordering on disk by sorting the revlogs by hash and suddenly
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180 performance of my kernel checkout benchmark dropped by ~10x because the
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181 "working set" of sectors visited no longer fit in the drive's cache and
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182 the workload switched from streaming to random I/O.
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183
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184 What we should really be doing is have workers read filenames from a
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185 ordered queue. This preserves locality and also keeps any worker from
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186 getting more than one file out of balance.
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187 '''
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188 for i in range(nslices):
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189 yield lst[i::nslices]