From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:37719) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QK6SG-00014R-5y for qemu-devel@nongnu.org; Wed, 11 May 2011 06:15:44 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1QK6SF-0000dy-9e for qemu-devel@nongnu.org; Wed, 11 May 2011 06:15:44 -0400 Received: from mtagate6.uk.ibm.com ([194.196.100.166]:46093) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QK6SF-0000av-1K for qemu-devel@nongnu.org; Wed, 11 May 2011 06:15:43 -0400 Received: from d06nrmr1707.portsmouth.uk.ibm.com (d06nrmr1707.portsmouth.uk.ibm.com [9.149.39.225]) by mtagate6.uk.ibm.com (8.13.1/8.13.1) with ESMTP id p4BAFSVI021024 for ; Wed, 11 May 2011 10:15:28 GMT Received: from d06av02.portsmouth.uk.ibm.com (d06av02.portsmouth.uk.ibm.com [9.149.37.228]) by d06nrmr1707.portsmouth.uk.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id p4BAFSZR1867864 for ; Wed, 11 May 2011 11:15:28 +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 p4BAFS8t016705 for ; Wed, 11 May 2011 04:15:28 -0600 From: Stefan Hajnoczi Date: Wed, 11 May 2011 11:15:23 +0100 Message-Id: <1305108925-26048-1-git-send-email-stefanha@linux.vnet.ibm.com> Subject: [Qemu-devel] [PATCH 0/2] 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 , Anthony Liguori , Venkateswararao Jujjuri 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 will follow shortly. Other areas of QEMU that could take advantage of coroutines include the VNC server, migration, and qemu-tools.