Use flock-style lock on Windows to limit number of concurrent links

pylib/gyp/win_tool.py

Index: pylib/gyp/win_tool.py
===================================================================
--- pylib/gyp/win_tool.py	(revision 1462)
+++ pylib/gyp/win_tool.py	(working copy)
@@ -13,6 +13,9 @@
 import shutil
 import subprocess
 import sys
+import win32con
+import win32file
+import pywintypes
 
 
 def main(args):
@@ -22,6 +25,22 @@
     sys.exit(exit_code)
 
 
+class LinkLock(object):
+  """A flock-style lock to limit the number of concurrent links to one. Based on
+  http://code.activestate.com/recipes/65203-portalocker-cross-platform-posixnt-api-for-flock-s/
+  """
+  def __enter__(self):
+    self.file = open('LinkLock', 'w+')
+    self.file_handle = win32file._get_osfhandle(self.file.fileno())
+    win32file.LockFileEx(self.file_handle, win32con.LOCKFILE_EXCLUSIVE_LOCK,
+                         0, -0x10000, pywintypes.OVERLAPPED())
+
+  def __exit__(self, type, value, traceback):
+    win32file.UnlockFileEx(
+        self.file_handle, 0, -0x10000, pywintypes.OVERLAPPED())
+    self.file.close()
+
+
 class WinTool(object):
   """This class performs all the Windows tooling steps. The methods can either
   be executed directly, or dispatched from an argument list."""
@@ -68,14 +87,15 @@
     '   Creating library ui.dll.lib and object ui.dll.exp'
     This happens when there are exports from the dll or exe.
     """
-    env = self._GetEnv(arch)
-    popen = subprocess.Popen(args, shell=True, env=env,
-                             stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
-    out, _ = popen.communicate()
-    for line in out.splitlines():
-      if not line.startswith('   Creating library '):
-        print line
-    return popen.returncode
+    with LinkLock():
+      env = self._GetEnv(arch)
+      popen = subprocess.Popen(args, shell=True, env=env,
+                               stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
+      out, _ = popen.communicate()
+      for line in out.splitlines():
+        if not line.startswith('   Creating library '):
+          print line
+      return popen.returncode
 
   def ExecManifestWrapper(self, arch, *args):
     """Run manifest tool with environment set. Strip out undesirable warning