workers: implemented worker on windows

This change implements thread based worker on windows.
The handling of exception from within threads will happen in separate diff.

The worker is for now used in mercurial/merge.py and in lfs extension

After multiple tests and milions of files materiealized, thousands lfs fetched
it seems that neither merge.py nor lfs/blobstore.py is thread unsafe. I also
looked through the code and besides the backgroundfilecloser (handled in base
of this) things look good.

The performance boost of this on windows is

~50% for sparse --enable-profile
* Speedup of hg up/rebase - not exactly measured

Test Plan:
Ran 10s of hg sparse --enable-profile and --disable-profile operations on large profiles and verified that workers are running. Used sysinternals suite to see that all threads are spawned and run as they should

Run various other operations on the repo including update and rebase

Ran tests on CentOS and all tests that pass on @ pass here

Differential Revision: https://phab.mercurial-scm.org/D1458

mercurial/worker.py

@@ -1,240 +1,285 b''
 # worker.py - master-slave parallelism support
 #
 # Copyright 2013 Facebook, Inc.
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 from __future__ import absolute_import
 
 import errno
 import os
 import signal
 import sys
+import threading
 
 from .i18n import _
 from . import (
     encoding,
     error,
     pycompat,
     scmutil,
     util,
 )
 
 def countcpus():
     '''try to count the number of CPUs on the system'''
 
     # posix
     try:
         n = int(os.sysconf(r'SC_NPROCESSORS_ONLN'))
         if n > 0:
             return n
     except (AttributeError, ValueError):
         pass
 
     # windows
     try:
         n = int(encoding.environ['NUMBER_OF_PROCESSORS'])
         if n > 0:
             return n
     except (KeyError, ValueError):
         pass
 
     return 1
 
 def _numworkers(ui):
     s = ui.config('worker', 'numcpus')
     if s:
         try:
             n = int(s)
             if n >= 1:
                 return n
         except ValueError:
             raise error.Abort(_('number of cpus must be an integer'))
     return min(max(countcpus(), 4), 32)
 
-if pycompat.isposix:
+if pycompat.isposix or pycompat.iswindows:
     _startupcost = 0.01
 else:
     _startupcost = 1e30
 
 def worthwhile(ui, costperop, nops):
     '''try to determine whether the benefit of multiple processes can
     outweigh the cost of starting them'''
     linear = costperop * nops
     workers = _numworkers(ui)
     benefit = linear - (_startupcost * workers + linear / workers)
     return benefit >= 0.15
 
 def worker(ui, costperarg, func, staticargs, args):
     '''run a function, possibly in parallel in multiple worker
     processes.
 
     returns a progress iterator
 
     costperarg - cost of a single task
 
     func - function to run
 
     staticargs - arguments to pass to every invocation of the function
 
     args - arguments to split into chunks, to pass to individual
     workers
     '''
     if worthwhile(ui, costperarg, len(args)):
         return _platformworker(ui, func, staticargs, args)
     return func(*staticargs + (args,))
 
 def _posixworker(ui, func, staticargs, args):
     rfd, wfd = os.pipe()
     workers = _numworkers(ui)
     oldhandler = signal.getsignal(signal.SIGINT)
     signal.signal(signal.SIGINT, signal.SIG_IGN)
     pids, problem = set(), [0]
     def killworkers():
         # unregister SIGCHLD handler as all children will be killed. This
         # function shouldn't be interrupted by another SIGCHLD; otherwise pids
         # could be updated while iterating, which would cause inconsistency.
         signal.signal(signal.SIGCHLD, oldchldhandler)
         # if one worker bails, there's no good reason to wait for the rest
         for p in pids:
             try:
                 os.kill(p, signal.SIGTERM)
             except OSError as err:
                 if err.errno != errno.ESRCH:
                     raise
     def waitforworkers(blocking=True):
         for pid in pids.copy():
             p = st = 0
             while True:
                 try:
                     p, st = os.waitpid(pid, (0 if blocking else os.WNOHANG))
                     break
                 except OSError as e:
                     if e.errno == errno.EINTR:
                         continue
                     elif e.errno == errno.ECHILD:
                         # child would already be reaped, but pids yet been
                         # updated (maybe interrupted just after waitpid)
                         pids.discard(pid)
                         break
                     else:
                         raise
             if not p:
                 # skip subsequent steps, because child process should
                 # be still running in this case
                 continue
             pids.discard(p)
             st = _exitstatus(st)
             if st and not problem[0]:
                 problem[0] = st
     def sigchldhandler(signum, frame):
         waitforworkers(blocking=False)
         if problem[0]:
             killworkers()
     oldchldhandler = signal.signal(signal.SIGCHLD, sigchldhandler)
     ui.flush()
     parentpid = os.getpid()
     for pargs in partition(args, workers):
         # make sure we use os._exit in all worker code paths. otherwise the
         # worker may do some clean-ups which could cause surprises like
         # deadlock. see sshpeer.cleanup for example.
         # override error handling *before* fork. this is necessary because
         # exception (signal) may arrive after fork, before "pid =" assignment
         # completes, and other exception handler (dispatch.py) can lead to
         # unexpected code path without os._exit.
         ret = -1
         try:
             pid = os.fork()
             if pid == 0:
                 signal.signal(signal.SIGINT, oldhandler)
                 signal.signal(signal.SIGCHLD, oldchldhandler)
 
                 def workerfunc():
                     os.close(rfd)
                     for i, item in func(*(staticargs + (pargs,))):
                         os.write(wfd, '%d %s\n' % (i, item))
                     return 0
 
                 ret = scmutil.callcatch(ui, workerfunc)
         except: # parent re-raises, child never returns
             if os.getpid() == parentpid:
                 raise
             exctype = sys.exc_info()[0]
             force = not issubclass(exctype, KeyboardInterrupt)
             ui.traceback(force=force)
         finally:
             if os.getpid() != parentpid:
                 try:
                     ui.flush()
                 except: # never returns, no re-raises
                     pass
                 finally:
                     os._exit(ret & 255)
         pids.add(pid)
     os.close(wfd)
     fp = os.fdopen(rfd, pycompat.sysstr('rb'), 0)
     def cleanup():
         signal.signal(signal.SIGINT, oldhandler)
         waitforworkers()
         signal.signal(signal.SIGCHLD, oldchldhandler)
         status = problem[0]
         if status:
             if status < 0:
                 os.kill(os.getpid(), -status)
             sys.exit(status)
     try:
         for line in util.iterfile(fp):
             l = line.split(' ', 1)
             yield int(l[0]), l[1][:-1]
     except: # re-raises
         killworkers()
         cleanup()
         raise
     cleanup()
 
 def _posixexitstatus(code):
     '''convert a posix exit status into the same form returned by
     os.spawnv
 
     returns None if the process was stopped instead of exiting'''
     if os.WIFEXITED(code):
         return os.WEXITSTATUS(code)
     elif os.WIFSIGNALED(code):
         return -os.WTERMSIG(code)
 
-if not pycompat.iswindows:
+def _windowsworker(ui, func, staticargs, args):
+    class Worker(threading.Thread):
+        def __init__(self, taskqueue, resultqueue, func, staticargs,
+                     group=None, target=None, name=None, verbose=None):
+            threading.Thread.__init__(self, group=group, target=target,
+                                      name=name, verbose=verbose)
+            self._taskqueue = taskqueue
+            self._resultqueue = resultqueue
+            self._func = func
+            self._staticargs = staticargs
+
+        def run(self):
+            while not self._taskqueue.empty():
+                try:
+                    args = self._taskqueue.get_nowait()
+                    for res in self._func(*self._staticargs + (args,)):
+                        self._resultqueue.put(res)
+                except util.empty:
+                    break
+
+    workers = _numworkers(ui)
+    threads = []
+    resultqueue = util.queue()
+    taskqueue = util.queue()
+    # partition work to more pieces than workers to minimize the chance
+    # of uneven distribution of large tasks between the workers
+    for pargs in partition(args, workers * 20):
+        taskqueue.put(pargs)
+    for _i in range(workers):
+        t = Worker(taskqueue, resultqueue, func, staticargs)
+        threads.append(t)
+        t.start()
+    while any(t.is_alive() for t in threads):
+        while not resultqueue.empty():
+            yield resultqueue.get()
+        t = threads[0]
+        t.join(0.05)
+        if not t.is_alive():
+            threads.remove(t)
+    while not resultqueue.empty():
+        yield resultqueue.get()
+
+if pycompat.iswindows:
+    _platformworker = _windowsworker
+else:
     _platformworker = _posixworker
     _exitstatus = _posixexitstatus
 
 def partition(lst, nslices):
     '''partition a list into N slices of roughly equal size
 
     The current strategy takes every Nth element from the input. If
     we ever write workers that need to preserve grouping in input
     we should consider allowing callers to specify a partition strategy.
 
     mpm is not a fan of this partitioning strategy when files are involved.
     In his words:
 
         Single-threaded Mercurial makes a point of creating and visiting
         files in a fixed order (alphabetical). When creating files in order,
         a typical filesystem is likely to allocate them on nearby regions on
         disk. Thus, when revisiting in the same order, locality is maximized
         and various forms of OS and disk-level caching and read-ahead get a
         chance to work.
 
         This effect can be quite significant on spinning disks. I discovered it
         circa Mercurial v0.4 when revlogs were named by hashes of filenames.
         Tarring a repo and copying it to another disk effectively randomized
         the revlog ordering on disk by sorting the revlogs by hash and suddenly
         performance of my kernel checkout benchmark dropped by ~10x because the
         "working set" of sectors visited no longer fit in the drive's cache and
         the workload switched from streaming to random I/O.
 
         What we should really be doing is have workers read filenames from a
         ordered queue. This preserves locality and also keeps any worker from
         getting more than one file out of balance.
     '''
     for i in range(nslices):
         yield lst[i::nslices]