tree 8ddfd7aa65bfb93a1c77d1edfa0f4c5576cad52e
parent cb365646a942ed58aae053064b2048a415337ba2
author Paolo Bonzini <pbonzini@redhat.com> 1380090059 +0800
committer Paolo Bonzini <pbonzini@redhat.com> 1382023855 +0200

qemu-thread: add QemuEvent

This emulates Win32 manual-reset events using futexes or conditional
variables.  Typical ways to use them are with multi-producer,
single-consumer data structures, to test for a complex condition whose
elements come from different threads:

    for (;;) {
        qemu_event_reset(ev);
        ... test complex condition ...
        if (condition is true) {
            break;
        }
        qemu_event_wait(ev);
    }

Or more efficiently (but with some duplication):

    ... evaluate condition ...
    while (!condition) {
        qemu_event_reset(ev);
        ... evaluate condition ...
        if (!condition) {
            qemu_event_wait(ev);
            ... evaluate condition ...
        }
    }

QemuEvent provides a very fast userspace path in the common case when
no other thread is waiting, or the event is not changing state.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>