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Date: Tue, 13 Jan 2015 10:38:36 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [RFC PATCH v7 12/21] replay: recording and
	replaying clock ticks
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To: Pavel Dovgaluk <Pavel.Dovgaluk@ispras.ru>, qemu-devel@nongnu.org
Cc: peter.maydell@linaro.org, peter.crosthwaite@xilinx.com, alex.bennee@linaro.org, mark.burton@greensocs.com, real@ispras.ru, batuzovk@ispras.ru, maria.klimushenkova@ispras.ru, afaerber@suse.de, fred.konrad@greensocs.com



On 13/01/2015 10:21, Pavel Dovgaluk wrote:
>>> +/*! Reads next clock event from the input. */
>>> > > +int64_t replay_read_clock(unsigned int kind)
>>> > > +{
>>> > > +    if (kind >= REPLAY_CLOCK_COUNT) {
>>> > > +        fprintf(stderr, "invalid clock ID %d for replay\n", kind);
>>> > > +        exit(1);
>>> > > +    }
>>> > > +
>>> > > +    replay_exec_instructions();
>>> > > +
>>> > > +    if (replay_file) {
>>> > > +        if (skip_async_events(EVENT_CLOCK + kind)) {
>>> > > +            replay_read_next_clock(kind);
>>> > > +        }
>>> > > +        int64_t ret = replay_state.cached_clock[kind];
>>> > > +
>>> > > +        return ret;
>>> > > +    }
>>> > > +
>>> > > +    fprintf(stderr, "REPLAY INTERNAL ERROR %d\n", __LINE__);
>>> > > +    exit(1);
>>> > > +}
>> > 
>> > Is this thread safe?  
> It is, because order of main_loop and cpu_exec executions is protected
> by global mutex.
> 

Please document exactly which globals are protected by the rr QemuMutex,
and which by the global mutex.  But I think as many variables as
possible should be protected by the rr QemuMutex, for two reasons:

1) people are working on threaded TCG.  While SMP record/replay is a
whole different story, even UP TCG will be multithreaded.

2) in the end it makes reviewing the code simpler.

Paolo