Re: [ECOS] ecos sync problem: Does it work well?

[张 亮 <johnsonest at hotmail dot com>]

Gary,
   maybe you make mistakes.i am level-headed!

> From: "Gary D. Thomas" <gary dot thomas at mind dot be>
> To: 寮?浜?<johnsonest at hotmail dot com>
> CC: eCos Discussion 
<ecos-discuss at sources dot redhat dot com>,nickg at calivar dot demon dot co dot uk
> Subject: Re: [ECOS] ecos sync problem: Does it work well?
> Date: 04 Mar 2003 22:54:55 -0700
>
> On Tue, 2003-03-04 at 22:25, 寮?浜?wrote:
> >
> > Hi,nickg!
> >      in support to tcp/ip stack,ecos packs two new sync function:
> >        cyg_tsleep(...)
> >        cyg_wakeup(...)
> > in synch.c file.
> >     according to ecos scheduler,I doubt it does not work well as 
following:
> >
>
> Actually, this code works just fine, thank you.
>
> Have you ever tried any of this code, or do you just sit up late
> at night and read it to ask questions?
>
> > int
> > cyg_tsleep(void *chan, int pri, char *wmesg, int timo)
> > {
> >     int i, res = 0;
> >     struct wakeup_event *ev;
> >     cyg_tick_count_t sleep_time;
> >     cyg_handle_t self = cyg_thread_self();
> >     int old_splflags = 0; // no flags held
> >
> >     cyg_scheduler_lock();//*******************lock=1,threads switch 
will be
> > impossible until last 
cyg_scheduler_unlock(),right?********************/
> >
> >     // Safely find a free slot:
> >     for (i = 0, ev = wakeup_list;  i < CYGPKG_NET_NUM_WAKEUP_EVENTS;  
i++,
> > ev++) {
> >         if (ev->chan == 0)
> >         {
> >             ev->chan = chan;
> >             break;
> >         }
> >     }
> >     CYG_ASSERT( i <  CYGPKG_NET_NUM_WAKEUP_EVENTS, "no sleep slots" );
> >     CYG_ASSERT( 1 == cyg_scheduler_read_lock(),
> >                 "Tsleep - called with scheduler locked" );
> >     // Defensive:
> >     if ( i >= CYGPKG_NET_NUM_WAKEUP_EVENTS ) {
> >         cyg_scheduler_unlock();
> >         return ETIMEDOUT;
> >     }
> >
> >     // If we are the owner, then we must release the mutex when
> >     // we wait.
> >     if ( self == splx_thread ) {
> >         old_splflags = spl_state; // Keep them for restoration
> >         CYG_ASSERT( spl_state, "spl_state not set" );
> >         // Also want to assert that the mutex is locked...
> >         CYG_ASSERT( splx_mutex.locked, "Splx mutex not locked" );
> >         CYG_ASSERT( (cyg_handle_t)splx_mutex.owner == self, "Splx mutex 
not
> > mine" );
> >         splx_thread = 0;
> >         spl_state = 0;
> >         cyg_mutex_unlock( &splx_mutex );
> >     }
> >
> >     // Re-initialize the semaphore - it might have counted up 
arbitrarily
> >     // in the time between a prior sleeper being signalled and them
> >     // actually running.
> >     cyg_semaphore_init(&ev->sem, 0);
> >
> >     // This part actually does the wait:
> >     // As of the new kernel, we can do this without unlocking the 
scheduler
> >     if (timo) {
> >         sleep_time = cyg_current_time() + timo;
> >        if (!cyg_semaphore_timed_wait(&ev->sem, sleep_time)) {
> > /**********lock will >1,never wait!!!*****************************/
>
> Wrong; read the scheduling code - it handle this case properly.
//////// this is cyg_semaphore_timed_wait(..) lock =2///////////////////
        Cyg_Scheduler::lock();

   CYG_INSTRUMENT_CNTSEM( CLAIM, this, count );
       
   if ( 0 < count ) {
       count--;
       Cyg_Scheduler::unlock();
   }
   else {

       // Put thread in sleep state before setting timer since if the
       // timeout is in the past, it will be re-awoken
       // immediately. If this happens then wake_reason will not be
       // NONE.
       
       self->sleep();

       self->set_timer( abs_timeout, Cyg_Thread::TIMEOUT );

       // only enqueue if the timeout did not already happen
       if( Cyg_Thread::NONE == self->get_wake_reason() )
           queue.enqueue( self );

       CYG_INSTRUMENT_CNTSEM( WAIT, this, 0 );

       
       Cyg_Scheduler::unlock();
////////////// in Cyg_Scheduler::unlock(),_lock=2-1=1 >0,unlock_inner(...) 
will never be called!
     so threads switch is impossible!
inline void Cyg_Scheduler::unlock()
{
   
   cyg_ucount32 __lock = get_sched_lock() - 1;
   
   if( __lock == 0 ) unlock_inner(0);
   else set_sched_lock(__lock);
}
////////////////////////////////////////////////////////////////////////
> >             if( cyg_current_time() >= sleep_time )
> >                 res = ETIMEDOUT;
> >             else
> >                 res = EINTR;
> >         }
> >     } else {
> >         if (!cyg_semaphore_wait(&ev->sem) ) {**********never wait for
> > lock>1
> >             res = EINTR;
> >         }
> >     }
> >
> >     ev->chan = 0;  // Free the slot - the wakeup call cannot do this.
> >
> >     if ( old_splflags ) { // restore to previous state
> >         // As of the new kernel, we can do this with the scheduler 
locked
> >         cyg_mutex_lock( &splx_mutex ); // this might wait
> >         CYG_ASSERT( 0 == splx_thread, "Splx thread set in tsleep" );
> >         CYG_ASSERT( 0 == spl_state, "spl_state set in tsleep" );
> >         splx_thread = self; // got it now...
> >         spl_state = old_splflags;
> >     }
> >
> >     cyg_scheduler_unlock();/****************till here,lock=0,threads 
switch
> > is possible,this means tsleep will never sleep!!!*************** /
>
> You can only get here *after* waiting above.
>
> >     return res;
> > }
> >
> >
> >
> > right?
> > but i do not know why redhat reported that stack works well?
> >
> >
> > BRS
> > johnsonest
> >
> > _________________________________________________________________
> > ??垂涓?浇 MSN Explorer:   http://explorer.msn.com/lccn
> >
> >
> > --
> > Before posting, please read the FAQ: http://sources.redhat.com/fom/ecos
> > and search the list archive: http://sources.redhat.com/ml/ecos-discuss
>
> --
> .--------------------------------------------------------.
> |       Mind: Embedded Linux and eCos Development        |
> |--------------------------------------------------------|
> | Gary Thomas              email:  gary dot thomas at mind dot be   |
> | Mind ( http://mind.be )  tel:    +1 (970) 229-1963     |
> | gpg: http://www.chez-thomas.org/gary/gpg_key.asc       |
> '--------------------------------------------------------'


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