[ECOS] Scheduler lock in Doug Lea's mallock implementation

[bob.koninckx@o-3s.com]

Hi,

Can someone explain me why the default memory allocator locks the scheduler? I would expect it to be legitimate for a low priority thread with no real time constraints to do dynamic memory allocation without influencing the real-time behaviour of threads with real-time constraints, as long as they have a higher priority. We experienced timing problems with high priority real-time threads that do not touch the heap because of dynamic memory allocation in a lower priority thread without real-time constraints and traced it down to the code snippet from packages/services/memalloc/common/current/include/mempolt2.inl below

// get some memory; wait if none available
template <class T>
inline cyg_uint8 *
Cyg_Mempolt2<T>::alloc( cyg_int32 size )
{
    CYG_REPORT_FUNCTION();


    // Prevent preemption
    Cyg_Scheduler::lock();
    CYG_ASSERTCLASS( this, "Bad this pointer");


    cyg_uint8 *ret;
    ret = pool.try_alloc( size );
    if ( ret ) {
        Cyg_Scheduler::unlock();
        CYG_ASSERTCLASS( this, "Bad this pointer");
        CYG_REPORT_RETVAL( ret );
        return ret;
    }


    Cyg_Thread *self = Cyg_Thread::self();


    Mempolt2WaitInfo waitinfo( size );


    CYG_MEMALLOC_FAIL(size);


    self->set_wait_info( (CYG_ADDRWORD)&waitinfo );
    self->set_sleep_reason( Cyg_Thread::WAIT );
    self->sleep();
    queue.enqueue( self );


    CYG_ASSERT( 1 == Cyg_Scheduler::get_sched_lock(),
                "Called with non-zero scheduler lock");


    // Unlock scheduler and allow other threads to run
    Cyg_Scheduler::unlock();
[...]

Thanks,

Bob



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