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| author | Paolo Bonzini <pbonzini@redhat.com> | 2017-01-12 19:07:59 +0100 |
|---|---|---|
| committer | Stefan Hajnoczi <stefanha@redhat.com> | 2017-01-16 13:25:18 +0000 |
| commit | 7c690fd1931f0908b18f7034b5d71d7b27ca59ef (patch) | |
| tree | fdc01d4b37919eb554fa3ed65d54138694f9ed58 /docs | |
| parent | b92d9a91abae1569ac499f72fbb90ee7b0ae5398 (diff) | |
| download | qemu-7c690fd1931f0908b18f7034b5d71d7b27ca59ef.tar.gz | |
aio: document locking
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>
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/multiple-iothreads.txt | 13 |
1 files changed, 5 insertions, 8 deletions
diff --git a/docs/multiple-iothreads.txt b/docs/multiple-iothreads.txt index 0e7cdb2c28..e4d340bbb7 100644 --- a/docs/multiple-iothreads.txt +++ b/docs/multiple-iothreads.txt @@ -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 ------------------------------ |