Add --jobs support to gclient. --jobs=1 is still the default for now.

gclient_utils.py

Index: gclient_utils.py
diff --git a/gclient_utils.py b/gclient_utils.py
index c530f4cb4cd79078635de9fe26a0912023e426a0..b2b009314036ea3e8fb5910e27c78d78966eeb7c 100644
--- a/gclient_utils.py
+++ b/gclient_utils.py
@@ -21,6 +21,7 @@ import re
 import stat
 import subprocess
 import sys
+import threading
 import time
 import threading
 import xml.dom.minidom
@@ -378,21 +379,30 @@ class WorkItem(object):
 
 
 class ExecutionQueue(object):
-  """Dependencies sometime needs to be run out of order due to From() keyword.
+  """Runs a set of WorkItem that have interdependencies and were WorkItem are
+  added as they are processed.
 
-  This class manages that all the required dependencies are run before running
-  each one.
+  In gclient's case, Dependencies sometime needs to be run out of order due to
+  From() keyword. This class manages that all the required dependencies are run
+  before running each one.
 
-  Methods of this class are multithread safe.
+  Methods of this class are thread safe.
   """
-  def __init__(self, progress):
-    self.lock = threading.Lock()
-    # List of WorkItem, Dependency inherits from WorkItem.
+  def __init__(self, jobs, progress):
+    """jobs specifies the number of concurrent tasks to allow. progress is a
+    Progress instance."""
+    # Set when a thread is done or a new item is enqueued.
+    self.ready_cond = threading.Condition()
+    # Maximum number of concurrent tasks.
+    self.jobs = jobs
+    # List of WorkItem, for gclient, these are Dependency instances.
     self.queued = []
     # List of strings representing each Dependency.name that was run.
     self.ran = []
     # List of items currently running.
     self.running = []
+    # Exceptions thrown if any.
+    self.exceptions = []
     self.progress = progress
     if self.progress:
       self.progress.update()
@@ -402,71 +412,99 @@ class ExecutionQueue(object):
     satisfied.
     """
     assert isinstance(d, WorkItem)
+    self.ready_cond.acquire()
     try:
-      self.lock.acquire()
       self.queued.append(d)
       total = len(self.queued) + len(self.ran) + len(self.running)
+      logging.debug('enqueued(%s)' % d.name)
+      if self.progress:
+        self.progress._total = total + 1
+        self.progress.update(0)
+      self.ready_cond.notifyAll()
     finally:
-      self.lock.release()
-    if self.progress:
-      self.progress._total = total + 1
-      self.progress.update(0)
+      self.ready_cond.release()
 
   def flush(self, *args, **kwargs):
     """Runs all enqueued items until all are executed."""
-    while self._run_one_item(*args, **kwargs):
-      pass
-    queued = []
-    running = []
+    self.ready_cond.acquire()
     try:
-      self.lock.acquire()
-      if self.queued:
-        queued = self.queued
-        self.queued = []
-      if self.running:
-        running = self.running
-        self.running = []
+      while True:
+        # Check for task to run first, then wait.
+        while True:
+          if self.exceptions:
+            # Systematically flush the queue when there is an exception logged
+            # in.
+            self.queued = []
+          # Flush threads that have terminated.
+          self.running = [t for t in self.running if t.isAlive()]
+          if not self.queued and not self.running:
+            break
+          if self.jobs == len(self.running):
+            break
+          for i in xrange(len(self.queued)):
+            # Verify its requirements.
+            for r in self.queued[i].requirements:
+              if not r in self.ran:
+                # Requirement not met.
+                break
+            else:
+              # Start one work item: all its requirements are satisfied.
+              d = self.queued.pop(i)
+              new_thread = self._Worker(self, d, args=args, kwargs=kwargs)
+              if self.jobs > 1:
+                # Start the thread.
+                self.running.append(new_thread)
+                new_thread.start()
+              else:
+                # Run the 'thread' inside the main thread.
+                new_thread.run()
+              break
+          else:
+            # Couldn't find an item that could run. Break out the outher loop.
+            break
+        if not self.queued and not self.running:
+          break
+        # We need to poll here otherwise Ctrl-C isn't processed.
+        self.ready_cond.wait(10)
+        # Something happened: self.enqueue() or a thread terminated. Loop again.
     finally:
-      self.lock.release()
+      self.ready_cond.release()
+    assert not self.running, 'Now guaranteed to be single-threaded'
+    if self.exceptions:
+      # TODO(maruel): Get back the original stack location.
+      raise self.exceptions.pop(0)
     if self.progress:
       self.progress.end()
-    if queued:
-      raise gclient_utils.Error('Entries still queued: %s' % str(queued))
-    if running:
-      raise gclient_utils.Error('Entries still queued: %s' % str(running))
 
-  def _run_one_item(self, *args, **kwargs):
-    """Removes one item from the queue that has all its requirements completed
-    and execute it.
+  class _Worker(threading.Thread):
+    """One thread to execute one WorkItem."""
+    def __init__(self, parent, item, args=(), kwargs=None):
+      threading.Thread.__init__(self, name=item.name or 'Worker')
+      self.args = args
+      self.kwargs = kwargs or {}
+      self.item = item
+      self.parent = parent
+
+    def run(self):
+      """Runs in its own thread."""
+      logging.debug('running(%s)' % self.item.name)
+      exception = None
+      try:
+        self.item.run(*self.args, **self.kwargs)
+      except Exception, e:
+        # TODO(maruel): Catch exception location.
+        exception = e
 
-    Returns False if no item could be run.
-    """
-    i = 0
-    d = None
-    try:
-      self.lock.acquire()
-      while i != len(self.queued) and not d:
-        d = self.queued.pop(i)
-        for r in d.requirements:
-          if not r in self.ran:
-            self.queued.insert(i, d)
-            d = None
-            break
-        i += 1
-      if not d:
-        return False
-      self.running.append(d)
-    finally:
-      self.lock.release()
-    d.run(*args, **kwargs)
-    try:
-      self.lock.acquire()
-      assert not d.name in self.ran
-      if not d.name in self.ran:
-        self.ran.append(d.name)
-      self.running.remove(d)
-      if self.progress:
-        self.progress.update(1)
-    finally:
-      self.lock.release()
-    return True
+      # This assumes the following code won't throw an exception. Bad.
+      self.parent.ready_cond.acquire()
+      try:
+        if exception:
+          self.parent.exceptions.append(exception)
+        if self.parent.progress:
+          self.parent.progress.update(1)
+        assert not self.item.name in self.parent.ran
+        if not self.item.name in self.parent.ran:
+          self.parent.ran.append(self.item.name)
+      finally:
+        self.parent.ready_cond.notifyAll()
+        self.parent.ready_cond.release()