On 21/06/12 10:00, Sergei Organov wrote: > A few clarifications below. > > Sergei Organov <o...@javad.com> writes: >> Hello, >> >> In the following sequence: >> >> cyg_scheduler_lock(); >> cyg_thread_suspend(thread); >> >> the second call returns immediately that is very surprising. Is it a bug >> or fature? > > 1. 'thread' is the current thread being executed so the suspend call asks > thread for suspending itself. > > 2. cyg_thread_delay(delay) returns immediately no matter what is 'delay' > value. > > 3. On the other hand, waiting on a primitive such as closed semaphore > works fine. > > Looks like a bug to me.
The form of many of these simple functions is to lock the scheduler, alter whatever state is appropriate, and then unlock the scheduler, with the understanding that any scheduling may happen at that point. Semaphore waits and other things are slightly different because they have changes to state to make after the wait, and need to retain the lock across it. In the cases you cite, any scheduling consequences of the calls made while the scheduler lock is claimed will occur when you finally unlock the scheduler yourself. One can argue that this is useful functionality, since it allows you to make a number of system state changes atomically under the scheduler lock. However, I don't actually know of any examples where this has been done, except in DSRs. Essentially locking the scheduler yourself is like running in a DSR, there is only a limited number of calls it makes sense to use, and their effects may be deferred until the scheduler lock returns to zero. While it might be possible to rewrite some of these routines to work even when the scheduler lock is already claimed, it would make them considerably more complex, larger, and thus less maintainable. -- Nick Garnett eCos Kernel Architect eCosCentric Limited http://www.eCosCentric.com The eCos experts Barnwell House, Barnwell Drive, Cambridge, UK. Tel: +44 1223 245571 Registered in England and Wales: Reg No: 4422071 -- Before posting, please read the FAQ: http://ecos.sourceware.org/fom/ecos and search the list archive: http://ecos.sourceware.org/ml/ecos-discuss
