Re: [boost] ARM help needed

From: Peter Dimov (pdimov_at_[hidden])
Date: 2008-04-09 18:07:19

Rene Rivera:

> Peter Dimov wrote:
>> Can someone with access to ARM please run
>> libs/smart_ptr/test/spinlock_test.cpp and/or take a look at
>> boost/detail/spinlock_gcc_arm.hpp? I've verified that it compiles, but 
>> can't
>> run it.
>
> What is the expected behavior? I get no output, no CPU usage, and an
> indefinite running time.

This means a deadlock. The test just locks and unlocks two spinlocks, the 
expected behavior is to return immediately. You can try 
spinlock_try_test.cpp which might produce some output.

Here's the relevant portion of spinlock_gcc_arm.hpp:

    bool try_lock()
    {
        int r;

        __asm__ __volatile__(
            "swp %0, %1, [%2]":
            "=r"( r ): // outputs
            "r"( 1 ), "r"( &v_ ): // inputs
            "memory", "cc" );

        return r == 0;
    }

    void lock()
    {
        for( unsigned k = 0; !try_lock(); ++k )
        {
            boost::detail::yield( k );
        }
    }

    void unlock()
    {
        __asm__ __volatile__( "" ::: "memory" );
        *const_cast< int volatile* >( &v_ ) = 0;
    }