From c033ead992a4e7bd8d031f25f3fa1256532c0540 Mon Sep 17 00:00:00 2001 From: Andreas Sandberg Date: Fri, 29 Nov 2013 14:36:10 +0100 Subject: base: Fix race in PollQueue and remove SIGALRM workaround There is a race between enabling asynchronous IO for a file descriptor and IO events happening on that descriptor. A SIGIO won't normally be delivered if an event is pending when asynchronous IO is enabled. Instead, the signal will be raised the next time there is an event on the FD. This changeset simulates a SIGIO by setting the async_io flag when setting up asynchronous IO for an FD. This causes the main event loop to poll all file descriptors to check for pending IO. As a consequence of this, the old SIGALRM hack should no longer be needed and is therefore removed. --- src/base/pollevent.cc | 10 ++++++++++ 1 file changed, 10 insertions(+) (limited to 'src/base/pollevent.cc') diff --git a/src/base/pollevent.cc b/src/base/pollevent.cc index 67e97f98f..9ed6df4fe 100644 --- a/src/base/pollevent.cc +++ b/src/base/pollevent.cc @@ -214,4 +214,14 @@ PollQueue::setupAsyncIO(int fd, bool set) if (fcntl(fd, F_SETFL, flags) == -1) panic("Could not set up async IO"); + + // The file descriptor might already have events pending. We won't + // see them if they occurred before we set the FASYNC + // flag. Simulate a SIGIO to ensure that the FD will be polled in + // next iteration of the simulation loop. We could just poll it, + // but this is much simpler. + if (set) { + async_event = true; + async_io = true; + } } -- cgit v1.2.3