[ECOS] problem with select()

Маврин Геннадий genamavr@mail.ru
Sun Apr 2 15:01:00 GMT 2006


I use the old version of ecos (ecos 2.0 downloaded at December 2003). But I searched the problem I have in the ecos bug tracking database and didn't find it.

I use select() function to wait when the descriptor will be ready for reading. Sometime select() returns 0 (time limit expire) but I am sure that the requested descriptor was ready for reading some time ago. After that if I perform the reading operation with this descriptor it completes successfully.

I think that I know the reason of this problem. The structure of cyg_pselect() function is:

int cyg_pselect( )
{
 while (!error)
 {
  for (mode = 0;  !error && mode < 3;  mode++)
  {
    ...
    // Checking the descriptors to be ready to requested operation
    ...
  }

  ...

  Cyg_Scheduler::lock();
  ...
  // Waiting for cyg_selwakeup() call
  ...
  Cyg_Scheduler::unlock();
 }
}

I think that the descriptor may come ready after the loop which checks the descriptors to be ready to requested operation but before Cyg_Scheduler::lock() function call. In this case cyg_pselect( ) will wait for descriptor even if this descriptor is ready. My idea is to move Cyg_Scheduler::lock() call up.

int cyg_pselect( )
{
 while (!error)
 {
  for (mode = 0;  !error && mode < 3;  mode++)
  {
    Cyg_Scheduler::lock();
    ...
    // Checking the descriptors to be ready to requested operation
    ...
  }

  ...

  // Waiting for cyg_selwakeup() call
  ...
  Cyg_Scheduler::unlock();
 }
}

Is my idea good or not?

Gennady

-- 
Before posting, please read the FAQ: http://ecos.sourceware.org/fom/ecos
and search the list archive: http://ecos.sourceware.org/ml/ecos-discuss



More information about the Ecos-discuss mailing list