[squid-dev] Moved PID file management from Coordinator to Master

[Amos Jeffries]

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On 14/01/2015 7:37 a.m., Tsantilas Christos wrote:
> On 01/12/2015 07:22 PM, Amos Jeffries wrote: On 12/01/2015 6:02
> a.m., Tsantilas Christos wrote:
>>>> Hi all, this patch moves pid file managment from coordinator 
>>>> process to master process.
>>>> 
>>>> This move is the first step necessary to avoid the following
>>>> race condition among PID file deletion and shared segment 
>>>> creation/destruction in SMP Squid:
>>>> 
>>>> O1) The old Squid Coordinator removes its PID file and quits.
>>>> N1) The system script notices Coordinator death and starts
>>>> the new Squid. N2) Shared segments are created by the new
>>>> Master process. O2) Shared segments are removed by the old
>>>> Master process. N3) New worker/disker processes fail due to
>>>> missing segments.
>>>> 
> 
> The Coordinator needs to continue coordinating activities over the
> SMP sockets until the workers are all shutdown and SMP sockets
> closed, only then should it do O2 and O1 (in that order).
> 
> The planned behaviour for worker shutdown is to: W1) early client
> FD closures into the beginning of the shutdown_timeout period W2)
> on each client closure or connection going idle, close it W3) at
> end of shutdown_timeout OR last client disconnect, release all 
> resources.
> 
> In that design the AsyncEngine still runs right up until the queue 
> completes draining. Using SMP sockets to inform Coordinator about 
> clean shutdown at the end.
> 
>> My sense is that the exit status can provide the same
>> functionality and also is easier to be implemented. If the worker
>> aborted early by a segfault then I am doubt that it will be able
>> to send a message to an SMP socket.
> 
> The Master process has no way to know if the workers are exiting
> early with no clients, or aborting on worker-specific
> shutdown_timeout values. But the coordinator can receive a
> terminated message from them over SMP sockets.
> 
>> We can use exit status.

Does the master process get exit status of *all* worker processes and
the sub-childs down N levels? It was my understanding that in SMP each
worker disker etc is a fork() and the child becomes new coordinator.


Amos
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