Date: Fri, 7 May 1999 13:36:51 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: Doug Rabson <dfr@nlsystems.com> Cc: current@FreeBSD.ORG Subject: Re: Debugging FreeBSD user threads with gdb Message-ID: <199905072036.NAA47016@apollo.backplane.com> References: <Pine.BSF.4.05.9905072123330.10400-100000@herring.nlsystems.com>
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:> :--- 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: dfr@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: dfr@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.
#define TIDINCR 32
struct tid {
struct tid *t_next;
int t_tid;
};
int maxtid = 1;
struct tid *tidpool;
struct tid *
alloctid(void)
{
struct tid *tid;
while ((tid = tidpool) == NULL) {
int i;
tidpool = malloc(sizeof(struct tid) * TIDINCR);
if (tidpool == NULL) {
... memory allocation failed ...
}
for (i = 0; i < TIDINCR; ++i) {
tidpool[i].t_tid = maxtid + i;
tidpool[i].t_next = &tidpool[i+1];
}
tidpool[i-1].t_next = NULL;
maxtid += TIDINCR;
}
tidpool = tid->t_next;
return(tid);
}
freetid(struct tid *tid)
{
tid->t_next = tidpool;
tidpool = tid;
}
-Matt
Matthew Dillon
<dillon@backplane.com>
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