before _Objects_Open

[Joel Sherrill]

吴昊 wrote:
> Joel Sherrill 写道:
>> 吴昊 wrote:
>>> Hi:
>>> I am reading source code of rtems-4.0.0.Here i got a problem:
>>> Before "_Objects_Open()",why _Thread_Disable_dispatch() is called?(e.g.
>>> in function"rtems_semaphore_create",the comment is " /* prevents
>>> deletion */"
>>>   
>> It prevents any context switches from occurring which effectively 
>> prevents
>> the deletion of the thread doing the create operation.  Between 
>> pulling the
>> semaphore structure off the inactive list and publishing it via 
>> _Objects_Open,
>> you don't want to get deleted since that would lose the object instance.
>>
>> --joel
>  In what case the other thread will delete the object which is being 
> created,since
>  the object id has not been returned yet?
Right you can't delete the object being created but you can delete the 
thread
calling object create.  This is the case we are worried about.

T1:  semaphore create
T2: delete T1

If the delete of T1 happens in the middle of semaphore create, then the
semaphore is neither in the inactive list nor allocated -- it is just lost.

--joel
>>> Have fun!
>>>
>>> Hao Wu
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>>> rtems-users at rtems.com
>>> http://rtems.rtems.org/mailman/listinfo/rtems-users
>>>   
>>
>