motorhead/qemu
1
0
Fork 0
mirror of https://github.com/Motorhead1991/qemu.git synced 2025-08-03 07:43:54 -06:00
Code Issues Projects Releases Packages Wiki Activity Actions

aio: document locking

Browse source 
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Message-id: 20170112180800.21085-10-pbonzini@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Paolo Bonzini 2017-01-12 19:07:59 +01:00 • committed by Stefan Hajnoczi
parent b92d9a91ab
commit 7c690fd193
2 changed files with 21 additions and 24 deletions
Download patch file Download diff file Expand all files Collapse all files

13
docs/multiple-iothreads.txt
View file

@ -84,9 +84,8 @@ How to synchronize with an IOThread
AioContext is not thread-safe so some rules must be followed when using file
descriptors, event notifiers, timers, or BHs across threads:
1. AioContext functions can be called safely from file descriptor, event
notifier, timer, or BH callbacks invoked by the AioContext. No locking is
necessary.
1. AioContext functions can always be called safely. They handle their
own locking internally.
2. Other threads wishing to access the AioContext must use
aio_context_acquire()/aio_context_release() for mutual exclusion. Once the
@ -94,16 +93,14 @@ context is acquired no other thread can access it or run event loop iterations
in this AioContext.
aio_context_acquire()/aio_context_release() calls may be nested. This
means you can call them if you're not sure whether #1 applies.
means you can call them if you're not sure whether #2 applies.
There is currently no lock ordering rule if a thread needs to acquire multiple
AioContexts simultaneously. Therefore, it is only safe for code holding the
QEMU global mutex to acquire other AioContexts.
Side note: the best way to schedule a function call across threads is to create
a BH in the target AioContext beforehand and then call qemu_bh_schedule(). No
acquire/release or locking is needed for the qemu_bh_schedule() call. But be
sure to acquire the AioContext for aio_bh_new() if necessary.
Side note: the best way to schedule a function call across threads is to call
aio_bh_schedule_oneshot(). No acquire/release or locking is needed.
AioContext and the block layer
------------------------------