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From: Philip Martin <philip.martin@wandisco.com>
To: Daniel Shahaf <d.s@daniel.shahaf.name>
Cc: dev@subversion.apache.org
Subject: Moving cancellation support to libsvn_subr
References: <20160129185522.A2F813A0249@svn01-us-west.apache.org>
	<20160130074708.GA30257@tarsus.local2> <87h9hsaf27.fsf@wandisco.com>
	<87d1sgad97.fsf__33268.2802960791$1454325642$gmane$org@wandisco.com>
	<20160207002204.GA13224@tarsus.local2> <87r3gncx0e.fsf@wandisco.com>
	<20160209032347.GA27845@tarsus.local2>
Date: Tue, 09 Feb 2016 18:19:02 +0000
In-Reply-To: <20160209032347.GA27845@tarsus.local2> (Daniel Shahaf's message
	of "Tue, 09 Feb 2016 03:23:47 +0000")
Message-ID: <87y4at927d.fsf_-_@wandisco.com>
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Daniel Shahaf <d.s@daniel.shahaf.name> writes:

> This fixes the race I mentioned, but I think we have another problem
> here: signum_cancelled is accessed by the signal handler so it must be
> of type 'static volatile sig_atomic_t' (C89 =C2=A74.7.1.1)...  but I don't
> think anything guarantees that signal numbers are representable as
> a sig_atomic_t.  On Linux/amd64 and FreeBSD they are, but that need not
> be the case everywhere.
>
> If we can't assume sig_atomic_t is at least as large as an int, I think
> we have to use the following roundabout method:

I did something similar in r1729422.

This code keeps growing and I'm thinking of moving both the signal
handler and cancellation handler to libsvn_subr.  We need some storage
for the volatiles and using pool memory implies a limited lifetime that
interacts badly with the signal handlers so I'm thinking of using static
storage in the library.  Something like:

  /* Setup signal handlers and return a cancellation handler. */
  svn_cancel_func_t svn_cmdline__setup_cancellation_handler();

  /* Return a signal that triggered cancellation or zero if no such
     signal. */
  int svn_cmdline__get_cancelled_signum();

and the application would do:

int main()
{
  apr_pool_t *pool;
  ...
  SVN_ERR(svn_client_create_context2(&ctx, ..., pool));
  ...
  ctx->cancel_func =3D svn_cmdline__setup_cancellation_handler();
  ...
  svn_pool_destroy(pool);
  ...
#ifndef WIN32
  {
    int signum =3D svn_cmdline__get_cancelled_signum();
    if (signum)
      kill(getpid(), signum);
  }
#endif

  return exit_code;
}

--=20
Philip Martin
WANdisco