Re: Problem with task component

[Adam Beneschan <adam@irvine.com>]

On Wednesday, September 19, 2012 11:22:08 AM UTC-7, Simon Wright wrote:
> If a Limited_Controlled type has a component of a task type, is it wrong
> to call an entry of the task from Initialize? When I do, the caller
> blocks.
> 
>    package Chips is
> 
>       type Chip is limited private;
> 
>    private 
> 
>       task type Polling_Task (For_Chip : not null access Chip) is
>          entry Start;
>          entry Stop;
>       end Polling_Task;
> 
>       type Chip is new Ada.Finalization.Limited_Controlled with record
>          Polling_Interval : Duration := 0.1; 
>          Poller           : Polling_Task (For_Chip => Chip'Access);
>       end record;
> 
>       overriding
>       procedure Initialize (C : in out Chip);
> 
> ...
> 
>    package body Chips is
> 
>       task body Polling_Task is
>       begin
>          accept Start;
>          ...
>       end Polling_Task;
> 
>       overriding
>       procedure Initialize (C : in out Chip)
>       is
>       begin
>          C.Poller.Start;      <=========== sticks here
>       end Initialize;
> 
> ...
> 
> If the task won't start executing until its instance is completely
> elaborated and initialized, I don't need the entry Start in any case.

I think the relevant rules are spelled out in 9.2.  This specifies when a task is *activated*, and a task can't accept an entry call until it's been activated.  For a task created by an allocator (including a task that's a component of an allocated object), the task activation is the last thing that the allocator does (and 7.6(12) confirms that it will happen after Initialize).  For a task created by a standalone object, e.g.

   procedure P is
      C : Chip;
      X1 : Some_Other_Object;
      X2 : Another_Object;
      ...
   begin
      ...

C.Poller won't get activated until *all* the declared objects have been initialized, including X1 and X2.

So I think it's always the case that a task won't be activated until the outermost object that encloses it have been completely initialized.  So it looks like you don't need Start.

                            -- Adam