bitbake: bitbake-worker/runqueue: Avoid unnecessary bytes object copies

declaring queue=b"" creates an object of types bytes().
bytes() is an immutable object, and therefore doing "self.queue = self.queue + r"
creates a new object containing "self.queue" concatenated with "r".

On my test setup, we are passing 180MB of data of "workerdata" to the bitbake-worker,
so those copies significantly slow down the initialization of the bitbake-worker.

Rather use bytearray() which a mutable type, and use extend() to avoid copies.
In my test setup, byterray.extend() is 10.000 times faster than copying the queue,
for a queue size of 180MB.

(Bitbake rev: 2302b5316091dff189e6c3f546341b2274ed9d0a)

Signed-off-by: Etienne Cordonnier <ecordonnier@snap.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/runqueue.py

@@ -3159,7 +3159,7 @@ class runQueuePipe():
         if pipeout:
             pipeout.close()
         bb.utils.nonblockingfd(self.input)
-        self.queue = b""
+        self.queue = bytearray()
         self.d = d
         self.rq = rq
         self.rqexec = rqexec
@@ -3178,7 +3178,7 @@ class runQueuePipe():
 
         start = len(self.queue)
         try:
-            self.queue = self.queue + (self.input.read(102400) or b"")
+            self.queue.extend(self.input.read(102400) or b"")
         except (OSError, IOError) as e:
             if e.errno != errno.EAGAIN:
                 raise