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Re: [PATCH] Introduce tids cache for dwfl_getthreads
- From: Mark Wielaard <mjw at redhat dot com>
- To: elfutils-devel at lists dot fedorahosted dot org
- Date: Mon, 16 Dec 2013 16:24:26 +0100
- Subject: Re: [PATCH] Introduce tids cache for dwfl_getthreads
On Mon, 2013-12-16 at 15:07 +0900, Masatake YAMATO wrote:
> dwfl_getthreads can be called once for the same Dwfl object. In
> dwfl_getthreads, directory entries under /proc/$pid/tasks are
> traversed and the directory descriptor points the end of
> /proc/$pid/tasks. Even if dwfl_getthreads called again, no
> more directory entry can be read from the descriptor.
Yes, that seems like a bug indeed.
> (1)rewinding the directory or (2) caching the threads at the initial
> traversing can permit calling dwfl_getthreads repeatedly.
> This patch implements (2). (2) is faster than (1) because
> (2) can avoid overheads of readdir.
I must say I would like (1) better. Because the process underlying the
Dwfl might have added/removed threads which would not been seen if we
cache the first readdir run.
It is also somewhat simpler to implement:
diff --git a/libdwfl/linux-pid-attach.c b/libdwfl/linux-pid-attach.c
index 45a0732..3d0716a 100644
@@ -164,6 +164,9 @@ pid_next_thread (Dwfl *dwfl __attribute__
((unused)), void *
struct pid_arg *pid_arg = dwfl_arg;
struct dirent *dirent;
+ /* Start fresh on first traversal. */
+ if (*thread_argp == NULL)
+ rewinddir (pid_arg->dir);
errno = 0;
It is of course slower than your solution.