Re: Destructors and program termination

Thu, 9 Aug 2007 11:39:48 CST
Lance Diduck wrote:

I have always found that programs that somehow has destructors that
can fail need to have their design reevaluated.

<aol>me too</aol>. I must admit, I was concerned when I thought about
the work that must be going on, basically just to free resources. It
should be simple and must not fail (so if a dtor calls routines that
can throw it should trap the exception and silently absorb it to
prevent it propagating outside the dtor).

I have recently coded something that uses cond vars, mutexes, threads
etc where I had to provide an orderly shutdown in the event that a
third-party library threw a wobblie. I made it so that the thread that
picks events up from library does so via a mechanism that allows me to
send messages as well as the API. The API rcvs its events by doing
select for a bunch of sockets so I create a pipe and add the file
descriptor to the collection of sockets being listened to. The thread
that does the listening I call the listening thread. The thread that
creates the listening thread I call the parent thread. This allows the
parent thread to send a msg to the listening thread to tell it to
stop. The parent thread owns a list that is protected by a mutex that
the listening thread can also access. This reminds me of the situation
described by the OP. So the parent threads waits on a cond var that is
signalled by the listening thread when the listening thread is about
to terminate. This means the parent thread can destroy the list
without having to worry about the listening thread trying to take a
lock on it.

-Andrew Marlow

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