On Fri, 7 May 1999, Matthew Dillon wrote:

> :> :--- uthread_create.c      1999/03/23 05:07:55     1.12
> :> :+++ uthread_create.c      1999/05/06 15:27:33
> :> :@@ -42,6 +42,8 @@
> :> : #include "pthread_private.h"
> :> : #include "libc_private.h"
> :> : 
> :> :+static int next_tid = 1;
> :> :+
> :> : int
> :> : pthread_create(pthread_t * thread, const pthread_attr_t * attr,
> :> :         void *(*start_routine) (void *), void *arg)
> :> :@@ -87,6 +89,7 @@
> :> :          } else {
> :> :                  /* Initialise the thread structure: */
> :> :                  memset(new_thread, 0, sizeof(struct pthread));
> :> :+                 new_thread->tid = next_tid++;
> :> :
> :> :Doug Rabson                               Mail:  d...@nlsystems.com
> :> :Nonlinear Systems Ltd.                    Phone: +44 181 442 9037
> :> 
> :>     Hmmm.   tid is only an int and some programs which create and destroy
> :>     threads a lot are almost certainly going to overflow it.  4 billion
> :>     is not hard to reach.  This can result in duplicate tid's.
> :
> :Didn't think of that.  It gets a bit ugly inside gdb since gdb needs a
> :single int to encode the pid and thread id.  I'm currently allowing 20
> :bits for the pid and 11 for the tid. Any ideas?
> :
> :--
> :Doug Rabson                          Mail:  d...@nlsystems.com
> :Nonlinear Systems Ltd.                       Phone: +44 181 442 9037
> 
>     Hmmm.  11 bits is only 2048 threads.  You are going to have problems
>     no matter what.
> 
>     You could have a pool of tid structures.  A simple freelist.  Pseudo
>     code below.  This would fix the unique-tid problem but it would not fix
>     the 2048 thread limit with gdb.

I can probably increase the field size of the tid up to about 14 bits (we
only have pids going up to 100000 I think). I would rather not do this
amount of work inside uthread; perhaps it would be better to make the
uthread store a 64bit unique number and then compress it down to a 14 bit
tid inside gdb by keeping a hash table or something similar.

Its going to be pretty hard to debug a program with 16k active threads so
I think this limit should be ok.

--
Doug Rabson                             Mail:  d...@nlsystems.com
Nonlinear Systems Ltd.                  Phone: +44 181 442 9037




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