workers: handling exceptions in windows workers

This adds handling of exceptions from worker threads and resurfaces them as if the function ran without workers.
If any of the threads throws, the main thread kills all running threads giving them 5 sec to handle the interruption and raises the first exception received.

We don't have to join threads if is_alive() is false

Test Plan:
Ran multiple updates/enable/disable sparse profile and things worked well

Ran test on CentOS- all tests passing on @ passed here

Added a forged exception into the worker code and got it properly resurfaced and the rest of workers killed: P58642088
PS C:\open\<repo>> ..\facebook-hg-rpms\build\hg\hg.exe --config extensions.fsmonitor=! sparse --enable-profile <profile>
updating [==>                                                                                                                ]  1300/39166 1m57sException in thread Thread-3:
Traceback (most recent call last):
  File "C:\open\facebook-hg-rpms\build\hg\hg-python\lib\threading.py", line 801, in __bootstrap_inner
    self.run()
  File "C:\open\facebook-hg-rpms\build\hg\mercurial\worker.py", line 244, in run
    raise e
Exception: Forged exception

Exception in thread Thread-2:
Traceback (most recent call last):
  File "C:\open\facebook-hg-rpms\build\hg\hg-python\lib\threading.py", line 801, in __bootstrap_inner
    self.run()
  File "C:\open\facebook-hg-rpms\build\hg\mercurial\worker.py", line 244, in run
    raise e
Exception: Forged exception
<...>
Traceback (most recent call last):
  File "C:\open\facebook-hg-rpms\build\hg\hgexe.py", line 41, in <module>
    dispatch.run()
  File "C:\open\facebook-hg-rpms\build\hg\mercurial\dispatch.py", line 85, in run
    status = (dispatch(req) or 0) & 255
  File "C:\open\facebook-hg-rpms\build\hg\mercurial\dispatch.py", line 173, in dispatch
    ret = _runcatch(req)
  File "C:\open\facebook-hg-rpms\build\hg\mercurial\dispatch.py", line 324, in _runcatch
    return _callcatch(ui, _runcatchfunc)
  File "C:\open\facebook-hg-rpms\build\hg\mercurial\dispatch.py", line 332, in _callcatch
    return scmutil.callcatch(ui, func)
  File "C:\open\facebook-hg-rpms\build\hg\mercurial\scmutil.py", line 154, in callcatch
    return func()
  File "C:\open\facebook-hg-rpms\build\hg\mercurial\dispatch.py", line 314, in _runcatchfunc
    return _dispatch(req)
  File "C:\open\facebook-hg-rpms\build\hg\mercurial\dispatch.py", line 951, in _dispatch
    cmdpats, cmdoptions)
  File "C:\open\facebook-hg-rpms\build\hg\hg-python\lib\site-packages\remotefilelog\__init__.py", line 415, in runcommand
    return orig(lui, repo, *args, **kwargs)
  File "C:\open\facebook-hg-rpms\build\hg\hg-python\lib\site-packages\hgext3rd\undo.py", line 118, in _runcommandwrapper
    result = orig(lui, repo, cmd, fullargs, *args)
  File "C:\open\facebook-hg-rpms\build\hg\hgext\journal.py", line 84, in runcommand
    return orig(lui, repo, cmd, fullargs, *args)
  File "C:\open\facebook-hg-rpms\build\hg\hg-python\lib\site-packages\hgext3rd\perftweaks.py", line 268, in _tracksparseprofiles
    res = runcommand(lui, repo, *args)
  File "C:\open\facebook-hg-rpms\build\hg\hg-python\lib\site-packages\hgext3rd\perftweaks.py", line 256, in _trackdirstatesizes
    res = runcommand(lui, repo, *args)
  File "C:\open\facebook-hg-rpms\build\hg\hg-python\lib\site-packages\hgext3rd\copytrace.py", line 144, in _runcommand
    return orig(lui, repo, cmd, fullargs, ui, *args, **kwargs)
  File "C:\open\facebook-hg-rpms\build\hg\hg-python\lib\site-packages\hgext3rd\fbamend\hiddenoverride.py", line 119, in runcommand
    result = orig(lui, repo, cmd, fullargs, *args)
  File "C:\open\facebook-hg-rpms\build\hg\mercurial\dispatch.py", line 712, in runcommand
    ret = _runcommand(ui, options, cmd, d)
  File "C:\open\facebook-hg-rpms\build\hg\mercurial\dispatch.py", line 959, in _runcommand
    return cmdfunc()
  File "C:\open\facebook-hg-rpms\build\hg\mercurial\dispatch.py", line 948, in <lambda>
    d = lambda: util.checksignature(func)(ui, *args, **strcmdopt)
  File "C:\open\facebook-hg-rpms\build\hg\mercurial\util.py", line 1183, in check
    return func(*args, **kwargs)
  File "C:\open\facebook-hg-rpms\build\hg\hg-python\lib\site-packages\hgext3rd\fbsparse.py", line 860, in sparse
    disableprofile=disableprofile, force=force)
  File "C:\open\facebook-hg-rpms\build\hg\hg-python\lib\site-packages\hgext3rd\fbsparse.py", line 949, in _config
    len, _refresh(ui, repo, oldstatus, oldsparsematch, force))
  File "C:\open\facebook-hg-rpms\build\hg\hg-python\lib\site-packages\hgext3rd\fbsparse.py", line 1116, in _refresh
    mergemod.applyupdates(repo, typeactions, repo[None], repo['.'], False)
  File "C:\open\facebook-hg-rpms\build\hg\hg-python\lib\site-packages\remotefilelog\__init__.py", line 311, in applyupdates
    return orig(repo, actions, wctx, mctx, overwrite, labels=labels)
  File "C:\open\facebook-hg-rpms\build\hg\mercurial\merge.py", line 1464, in applyupdates
    for i, item in prog:
  File "C:\open\facebook-hg-rpms\build\hg\mercurial\worker.py", line 286, in _windowsworker
    raise t.exception
Exception: Forged exception
PS C:\open\ovrsource>

Differential Revision: https://phab.mercurial-scm.org/D1459

mercurial/worker.py

@@ -214,18 +214,45 b' def _windowsworker(ui, func, staticargs,'
             self._resultqueue = resultqueue
             self._func = func
             self._staticargs = staticargs
+            self._interrupted = False
+            self.exception = None
+
+        def interrupt(self):
+            self._interrupted = True
 
         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
+            try:
+                while not self._taskqueue.empty():
+                    try:
+                        args = self._taskqueue.get_nowait()
+                        for res in self._func(*self._staticargs + (args,)):
+                            self._resultqueue.put(res)
+                            # threading doesn't provide a native way to
+                            # interrupt execution. handle it manually at every
+                            # iteration.
+                            if self._interrupted:
+                                return
+                    except util.empty:
+                        break
+            except Exception as e:
+                # store the exception such that the main thread can resurface
+                # it as if the func was running without workers.
+                self.exception = e
+                raise
+
+    threads = []
+    def killworkers():
+        for t in threads:
+            t.interrupt()
+        for t in threads:
+            # try to let the threads handle interruption, but don't wait
+            # indefintely. the thread could be in infinite loop, handling
+            # a very long task or in a deadlock situation
+            t.join(5)
+            if t.is_alive():
+                raise error.Abort(_('failed to join worker thread'))
 
     workers = _numworkers(ui)
-    threads = []
     resultqueue = util.queue()
     taskqueue = util.queue()
     # partition work to more pieces than workers to minimize the chance
@@ -236,12 +263,24 b' def _windowsworker(ui, func, staticargs,'
         t = Worker(taskqueue, resultqueue, func, staticargs)
         threads.append(t)
         t.start()
-    while any(t.is_alive() for t in threads):
+
+    while len(threads) > 0:
         while not resultqueue.empty():
             yield resultqueue.get()
-        t = threads[0]
-        t.join(0.05)
-        if not t.is_alive():
+        threads[0].join(0.05)
+        finishedthreads = [_t for _t in threads if not _t.is_alive()]
+        for t in finishedthreads:
+            if t.exception is not None:
+                try:
+                    killworkers()
+                except Exception:
+                    # pass over the workers joining failure. it is more
+                    # important to surface the inital exception than the
+                    # fact that one of workers may be processing a large
+                    # task and does not get to handle the interruption.
+                    ui.warn(_("failed to kill worker threads while handling "
+                              "an exception"))
+                raise t.exception
             threads.remove(t)
     while not resultqueue.empty():
         yield resultqueue.get()