From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:57167) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QKodz-0003xZ-Bg for qemu-devel@nongnu.org; Fri, 13 May 2011 05:26:48 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1QKodx-0003Me-TO for qemu-devel@nongnu.org; Fri, 13 May 2011 05:26:47 -0400 Received: from mtagate5.uk.ibm.com ([194.196.100.165]:52810) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QKodx-0003MI-LK for qemu-devel@nongnu.org; Fri, 13 May 2011 05:26:45 -0400 Received: from d06nrmr1307.portsmouth.uk.ibm.com (d06nrmr1307.portsmouth.uk.ibm.com [9.149.38.129]) by mtagate5.uk.ibm.com (8.13.1/8.13.1) with ESMTP id p4D9QiOe004792 for ; Fri, 13 May 2011 09:26:44 GMT Received: from d06av02.portsmouth.uk.ibm.com (d06av02.portsmouth.uk.ibm.com [9.149.37.228]) by d06nrmr1307.portsmouth.uk.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id p4D9QdOe2289764 for ; Fri, 13 May 2011 10:26:43 +0100 Received: from d06av02.portsmouth.uk.ibm.com (loopback [127.0.0.1]) by d06av02.portsmouth.uk.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id p4D9QdIL013662 for ; Fri, 13 May 2011 03:26:39 -0600 From: Stefan Hajnoczi Date: Fri, 13 May 2011 10:26:28 +0100 Message-Id: <1305278792-20933-1-git-send-email-stefanha@linux.vnet.ibm.com> Subject: [Qemu-devel] [PATCH v3 0/4] Coroutines for better asynchronous programming List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Kevin Wolf , Paolo Bonzini , Anthony Liguori , Blue Swirl QEMU is event-driven and suffers when blocking operations are performed because VM execution may be stopped until the operation completes. Therefore many operations that could block are performed asynchronously and a callback is invoked when the operation has completed. This allows QEMU to continue executing while the operation is pending. The downside to callbacks is that they split up code into many smaller functions, each of which is a single step in a state machine that quickly becomes complex and hard to understand. Callback functions also result in lots of noise as variables are packed and unpacked into temporary structs that pass state to the callback function. This patch series introduces coroutines as a solution for writing asynchronous code while still having a nice sequential control flow. The semantics are explained in the first patch. The second patch adds automated tests. A nice feature of coroutines is that it is relatively easy to take synchronous code and lift it into a coroutine to make it asynchronous. Work has been done to move qcow2 request processing into coroutines and thereby make it asynchronous (today qcow2 will perform synchronous metadata accesses). This qcow2 work is still ongoing and not quite ready for mainline yet. Coroutines are also being used for virtfs (virtio-9p) so I have submitted this patch now because virtfs patches that depend on coroutines are being published. Other areas of QEMU that could take advantage of coroutines include the VNC server, migration, and qemu-tools. v3: * Updated LGPL v2 license header to use web link * Removed atexit(3) pool freeing * Removed thread-local current/leader * Documented thread-safety limitation * Disabled trace events v2: * Added ./check-coroutine --lifecycle-benchmark for performance measurement * Split pooling into a separate patch with performance justification * Set maximum pool size to prevent holding onto too many free coroutines * Added atexit(3) handler to free pool * Coding style cleanups