killdaemons: close pid file before killing processes

With #serve enabled on Windows, I was getting occasional stacktraces like this:

  Errored test-hgweb-json.t: Traceback (most recent call last):
    File "./run-tests.py", line 724, in run
      self.tearDown()
    File "./run-tests.py", line 805, in tearDown
      killdaemons(entry)
    File "./run-tests.py", line 540, in killdaemons
      logfn=vlog)
    File "...\tests\killdaemons.py", line 94, in killdaemons
      os.unlink(pidfile)
  WindowsError: [Error 32] The process cannot access the file because it is
     being used by another process: '...\\hgtests.zmpqj3\\child80\\daemon.pids'

Adrian suggested using util.posixfile, which works.  However, the 'mercurial'
package isn't in sys.path when invoking run-tests.py, and it isn't clear that
hacking[1] it in is a good thing (especially for test-run-tests.t, which uses an
installation in a temp folder).

I tried using ProcessMonitor to figure out what the other process is, but that
monitoring slows things down to such a degree that the issue doesn't occur.  I
was ready to blame the virus scanner, but it happens without that too.

Looking at the code, I don't see anything that would have the pid file open.
But I was able to get through about 20 full test runs without an issue with this
minor change, whereas before it was pretty certain to hit this at least once in
two or three runs.

[1] https://www.mercurial-scm.org/pipermail/mercurial-devel/2017-May/097907.html

tests/killdaemons.py

@@ -1,104 +1,106 b''
 #!/usr/bin/env python
 
 from __future__ import absolute_import
 import errno
 import os
 import signal
 import sys
 import time
 
 if os.name =='nt':
     import ctypes
 
     def _check(ret, expectederr=None):
         if ret == 0:
             winerrno = ctypes.GetLastError()
             if winerrno == expectederr:
                 return True
             raise ctypes.WinError(winerrno)
 
     def kill(pid, logfn, tryhard=True):
         logfn('# Killing daemon process %d' % pid)
         PROCESS_TERMINATE = 1
         PROCESS_QUERY_INFORMATION = 0x400
         SYNCHRONIZE = 0x00100000
         WAIT_OBJECT_0 = 0
         WAIT_TIMEOUT = 258
         handle = ctypes.windll.kernel32.OpenProcess(
                 PROCESS_TERMINATE|SYNCHRONIZE|PROCESS_QUERY_INFORMATION,
                 False, pid)
         if handle == 0:
             _check(0, 87) # err 87 when process not found
             return # process not found, already finished
         try:
             r = ctypes.windll.kernel32.WaitForSingleObject(handle, 100)
             if r == WAIT_OBJECT_0:
                 pass # terminated, but process handle still available
             elif r == WAIT_TIMEOUT:
                 _check(ctypes.windll.kernel32.TerminateProcess(handle, -1))
             else:
                 _check(r)
 
             # TODO?: forcefully kill when timeout
             #        and ?shorter waiting time? when tryhard==True
             r = ctypes.windll.kernel32.WaitForSingleObject(handle, 100)
                                                        # timeout = 100 ms
             if r == WAIT_OBJECT_0:
                 pass # process is terminated
             elif r == WAIT_TIMEOUT:
                 logfn('# Daemon process %d is stuck')
             else:
                 _check(r) # any error
         except: #re-raises
             ctypes.windll.kernel32.CloseHandle(handle) # no _check, keep error
             raise
         _check(ctypes.windll.kernel32.CloseHandle(handle))
 
 else:
     def kill(pid, logfn, tryhard=True):
         try:
             os.kill(pid, 0)
             logfn('# Killing daemon process %d' % pid)
             os.kill(pid, signal.SIGTERM)
             if tryhard:
                 for i in range(10):
                     time.sleep(0.05)
                     os.kill(pid, 0)
             else:
                 time.sleep(0.1)
                 os.kill(pid, 0)
             logfn('# Daemon process %d is stuck - really killing it' % pid)
             os.kill(pid, signal.SIGKILL)
         except OSError as err:
             if err.errno != errno.ESRCH:
                 raise
 
 def killdaemons(pidfile, tryhard=True, remove=False, logfn=None):
     if not logfn:
         logfn = lambda s: s
     # Kill off any leftover daemon processes
     try:
-        fp = open(pidfile)
-        for line in fp:
-            try:
-                pid = int(line)
-                if pid <= 0:
-                    raise ValueError
-            except ValueError:
-                logfn('# Not killing daemon process %s - invalid pid'
-                      % line.rstrip())
-                continue
+        pids = []
+        with open(pidfile) as fp:
+            for line in fp:
+                try:
+                    pid = int(line)
+                    if pid <= 0:
+                        raise ValueError
+                except ValueError:
+                    logfn('# Not killing daemon process %s - invalid pid'
+                          % line.rstrip())
+                    continue
+                pids.append(pid)
+        for pid in pids:
             kill(pid, logfn, tryhard)
-        fp.close()
         if remove:
             os.unlink(pidfile)
     except IOError:
         pass
 
 if __name__ == '__main__':
     if len(sys.argv) > 1:
         path, = sys.argv[1:]
     else:
         path = os.environ["DAEMON_PIDS"]
 
     killdaemons(path)