From: Mark Wielaard <mark@klomp.org>
To: "Frank Ch. Eigler" <fche@redhat.com>
Cc: elfutils-devel@sourceware.org, amerey@redhat.com
Subject: Re: patch 1/2 debuginfod client
Date: Tue, 19 Nov 2019 15:57:00 -0000 [thread overview]
Message-ID: <7ca3cc662684459fe21801344f0899f5108a8a70.camel@klomp.org> (raw)
In-Reply-To: <20191118203324.GD2880@redhat.com>
Hi,
On Mon, 2019-11-18 at 15:33 -0500, Frank Ch. Eigler wrote:
> > > > Do you know how other libraries that use libcurl deal with this?
> > >
> > > I looked over some other libcurl users in fedora. Some don't worry
> > > about the issue at all, relying on implicit initialization, which is
> > > only safe if single-threaded. Others (libvirtd) do an explicitly
> > > invoked initialization function, which is also only safe if invoked
> > > from a single-threaded context.
> > >
> > > I think actually our way here, running the init function from the
> > > shared library constructor, is about the best possible. As long as
> > > the ld.so process is done as normal, it should be fine. Programs that
> > > use the elfutils trick of manual dlopen'ing libdebuginfod.so should do
> > > so only if they are single-threaded.
> >
> > But they cannot really control that... Since they might not know (and
> > really shouldn't care) that libdw lazily tries to dlopen
> > libdebuginfod.so which then pulls in libcurl and calls that global init
> > function...
> >
> > Could we do try to do the dlopen and global curl initialization from
> > libdw _init, or a ctor, to make sure it is done as early as possible?
>
> Doing a redundant initialization later is not a problem; there is a
> counter in there. The problematic case would be
> - a multithreaded application
> - loading debuginfod.so multiply concurrently somehow
> - and calling the solib ctor concurrently somehow
> - and all of this concurrently enough to defeat libcurl's init-counter
>
> IMHO, not worth worrying about. Someday libcurl will do the right
> thing (tm) and plop this initialization into their solib ctor.
I do worry about this because any multi-threaded app that uses libdw.so
might cause trouble because we dlopen libdebuginfod.so lazily and then
it will call curl_global_init () which explicitly says:
This function is not thread safe. You must not call it when any
other thread in the program (i.e. a thread sharing the same memory)
is running. This doesn't just mean no other thread that is using
libcurl. Because curl_global_init calls functions of other
libraries that are similarly thread unsafe, it could conflict with
any other thread that uses these other libraries.
That is why I think doing the dlopen of libdebuginfod.so eagerly from a
libdw.so constructor function or _init might be necessary to make sure
no other threads are running yet.
> > > > I was more thinking zero == infinity (no timeout).
> > >
> > > An unset environment variable should do that.
> >
> > Are you sure? If DEBUGINFOD_TIMEOUT isn't set, then it seems it
> > defaults to 5 seconds:
> >
> > /* Timeout for debuginfods, in seconds.
> > This env var must be set for debuginfod-client to run. */
> > static const char *server_timeout_envvar =
> > DEBUGINFOD_TIMEOUT_ENV_VAR;
> > static int server_timeout = 5;
> > [...]
> >
> > if (getenv(server_timeout_envvar))
> > server_timeout = atoi (getenv(server_timeout_envvar));
>
> OK, hm, we could make an -empty- but set environment variable mean
> 'infinity'. Then again, a user can also say =99999.
Yes. In this case even setting it to 600 probably feels like forever
anyway since someone is waiting on the file... :)
Cheers,
Mark
next prev parent reply other threads:[~2019-11-19 15:57 UTC|newest]
Thread overview: 78+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-28 19:04 patch 0/2 debuginfod submission Frank Ch. Eigler
2019-10-28 19:06 ` patch 1/2 debuginfod client Frank Ch. Eigler
2019-10-28 19:09 ` patch 2/2 debuginfod server etc Frank Ch. Eigler
2019-11-04 21:48 ` patch 3/3 debuginfod client interruptability Frank Ch. Eigler
2019-11-07 9:07 ` patch 4 debuginfod: symlink following mode Frank Ch. Eigler
2019-11-07 9:08 ` patch 5 debuginfod: prometheus metrics Frank Ch. Eigler
2019-11-15 17:26 ` Mark Wielaard
2019-11-15 17:58 ` Frank Ch. Eigler
2019-11-18 16:20 ` Mark Wielaard
2019-11-18 16:48 ` Frank Ch. Eigler
2019-11-19 16:13 ` Mark Wielaard
2019-11-15 16:49 ` patch 4 debuginfod: symlink following mode Mark Wielaard
2019-11-15 18:31 ` Frank Ch. Eigler
2019-11-18 16:27 ` Mark Wielaard
2019-11-15 16:16 ` patch 3/3 debuginfod client interruptability Mark Wielaard
2019-11-15 17:03 ` Aaron Merey
2019-11-15 17:35 ` Mark Wielaard
2019-11-15 18:14 ` Pedro Alves
2019-11-17 23:44 ` Mark Wielaard
2019-11-18 2:50 ` Frank Ch. Eigler
2019-11-18 9:24 ` Pedro Alves
2019-11-19 12:58 ` Mark Wielaard
2019-11-13 17:22 ` patch 2/2 debuginfod server etc Mark Wielaard
2019-11-14 11:54 ` Frank Ch. Eigler
2019-11-16 1:31 ` Mark Wielaard
2019-11-13 23:19 ` Mark Wielaard
2019-11-14 12:30 ` Frank Ch. Eigler
2019-11-18 14:17 ` Mark Wielaard
2019-11-18 18:41 ` Frank Ch. Eigler
2019-11-19 15:41 ` Mark Wielaard
2019-11-19 16:13 ` Frank Ch. Eigler
2019-11-19 20:11 ` Mark Wielaard
2019-11-19 21:15 ` Frank Ch. Eigler
2019-11-20 11:53 ` Mark Wielaard
2019-11-20 12:29 ` Frank Ch. Eigler
2019-11-21 14:16 ` Mark Wielaard
2019-11-21 15:40 ` Mark Wielaard
2019-11-21 16:01 ` Frank Ch. Eigler
2019-11-21 15:58 ` Frank Ch. Eigler
2019-11-21 16:37 ` Mark Wielaard
2019-11-21 17:18 ` Frank Ch. Eigler
2019-11-21 20:42 ` Mark Wielaard
2019-11-22 12:08 ` Mark Wielaard
2019-11-14 20:45 ` Mark Wielaard
2019-11-15 11:03 ` Mark Wielaard
2019-11-15 21:00 ` Frank Ch. Eigler
2019-11-18 15:01 ` Mark Wielaard
2019-11-15 14:40 ` Mark Wielaard
2019-11-15 19:54 ` Frank Ch. Eigler
2019-11-18 15:31 ` Mark Wielaard
2019-11-18 15:49 ` Frank Ch. Eigler
2019-11-12 11:12 ` patch 1/2 debuginfod client Mark Wielaard
2019-11-12 15:14 ` Frank Ch. Eigler
2019-11-12 21:59 ` Mark Wielaard
2019-11-14 0:33 ` Frank Ch. Eigler
2019-11-15 21:33 ` Mark Wielaard
2019-11-12 21:25 ` Mark Wielaard
2019-11-13 23:25 ` Frank Ch. Eigler
2019-11-16 0:46 ` Mark Wielaard
2019-11-16 18:53 ` Frank Ch. Eigler
2019-11-18 17:17 ` Mark Wielaard
2019-11-18 20:33 ` Frank Ch. Eigler
2019-11-19 15:57 ` Mark Wielaard [this message]
2019-11-19 16:20 ` Frank Ch. Eigler
2019-11-19 20:16 ` Mark Wielaard
2019-11-19 21:22 ` Frank Ch. Eigler
2019-11-20 12:50 ` Mark Wielaard
2019-11-20 13:30 ` Frank Ch. Eigler
2019-11-21 14:02 ` Mark Wielaard
2019-11-13 13:57 ` Mark Wielaard
2019-11-14 11:24 ` Frank Ch. Eigler
2019-11-16 0:52 ` Mark Wielaard
2019-11-16 2:28 ` Frank Ch. Eigler
2019-10-30 11:04 ` patch 0/2 debuginfod submission Mark Wielaard
2019-10-30 13:40 ` Frank Ch. Eigler
2019-10-30 14:12 ` Mark Wielaard
2019-10-30 18:11 ` Frank Ch. Eigler
2019-10-31 11:18 ` Mark Wielaard
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