optimize the sync worker

This change optimize the sync worker when we only have to listen on one
interface. While I'm here, I fixed a long and unnoticed outstanding issue when
we were accepting on multiple interfaces (wonder if someone really use it), at
some point soe interfaces were skipped.

gunicorn/workers/sync.py

@@ -21,13 +21,38 @@ from gunicorn import six
 
 class SyncWorker(base.Worker):
 
-    def run(self):
-        # self.socket appears to lose its blocking status after
-        # we fork in the arbiter. Reset it here.
-        for s in self.sockets:
-            s.setblocking(0)
+    def accept(self, listener):
+        client, addr = listener.accept()
+        client.setblocking(1)
+        util.close_on_exec(client)
+        self.handle(listener, client, addr)
 
-        ready = self.sockets
+    def wait(self, timeout):
+        try:
+            self.notify()
+            ret = select.select(self.sockets, [], self.PIPE, timeout)
+            if ret[0]:
+                return ret[0]
+
+        except select.error as e:
+            if e.args[0] == errno.EINTR:
+                return self.sockets
+            if e.args[0] == errno.EBADF:
+                if self.nr < 0:
+                    return self.sockets
+                else:
+                    return False
+            raise
+
+    def is_parent_alive(self):
+        # If our parent changed then we shut down.
+        if self.ppid != os.getppid():
+            self.log.info("Parent changed, shutting down: %s", self)
+            return False
+        return True
+
+    def run_for_one(self, timeout):
+        listener = self.sockets[0]
         while self.alive:
             self.notify()
 
@@ -35,51 +60,57 @@ class SyncWorker(base.Worker):
             # that no connection is waiting we fall down to the
             # select which is where we'll wait for a bit for new
             # workers to come give us some love.
+            try:
+                self.accept(listener)
+                # Keep processing clients until no one is waiting. This
+                # prevents the need to select() for every client that we
+                # process.
+                continue
 
-            for sock in ready:
+            except socket.error as e:
+                if e.args[0] not in (errno.EAGAIN, errno.ECONNABORTED,
+                        errno.EWOULDBLOCK):
+                    raise
+
+            if not self.is_parent_alive():
+                return
+
+            if not self.wait(timeout):
+                return
+
+    def run_for_multiple(self, timeout):
+        while self.alive:
+            self.notify()
+
+            ready = self.wait(timeout)
+            if not ready:
+                return
+
+            for listener in ready:
                 try:
-                    client, addr = sock.accept()
-                    client.setblocking(1)
-                    util.close_on_exec(client)
-                    self.handle(sock, client, addr)
-
-                    # Keep processing clients until no one is waiting. This
-                    # prevents the need to select() for every client that we
-                    # process.
-                    continue
-
+                    self.accept(listener)
                 except socket.error as e:
                     if e.args[0] not in (errno.EAGAIN, errno.ECONNABORTED,
                             errno.EWOULDBLOCK):
                         raise
 
-            # If our parent changed then we shut down.
-            if self.ppid != os.getppid():
-                self.log.info("Parent changed, shutting down: %s", self)
+            if not self.is_parent_alive():
                 return
 
-            try:
-                self.notify()
+    def run(self):
+        # if no timeout is given the worker will never wait and will
+        # use the CPU for nothing. This minimal timeout prevent it.
+        timeout = self.timeout or 0.5
 
-                # if no timeout is given the worker will never wait and will
-                # use the CPU for nothing. This minimal timeout prevent it.
-                timeout = self.timeout or 0.5
+        # self.socket appears to lose its blocking status after
+        # we fork in the arbiter. Reset it here.
+        for s in self.sockets:
+            s.setblocking(0)
 
-                ret = select.select(self.sockets, [], self.PIPE, timeout)
-                if ret[0]:
-                    ready = ret[0]
-                    continue
-            except select.error as e:
-                if e.args[0] == errno.EINTR:
-                    ready = self.sockets
-                    continue
-                if e.args[0] == errno.EBADF:
-                    if self.nr < 0:
-                        ready = self.sockets
-                        continue
-                    else:
-                        return
-                raise
+        if len(self.sockets) > 1:
+            self.run_for_multiple(timeout)
+        else:
+            self.run_for_one(timeout)
 
     def handle(self, listener, client, addr):
         req = None