From 7966faa931bfa9cf4ca53dd2d5b6e1eb0f174411 Mon Sep 17 00:00:00 2001
From: rsc <devnull@localhost>
Date: Thu, 23 Sep 2004 03:01:36 +0000
Subject: Continue fighting pthreads. Clean up thread library a bit too.

---
 src/libthread/chanprint.c  |   4 +-
 src/libthread/create.c     | 227 +++++++++++++++--------------
 src/libthread/debug.c      |   4 +-
 src/libthread/exec-unix.c  |  14 +-
 src/libthread/exec.c       |  82 -----------
 src/libthread/exit.c       |  31 +---
 src/libthread/id.c         |   8 +-
 src/libthread/iocall.c     |   5 +-
 src/libthread/ioproc.c     |   5 +-
 src/libthread/main.c       | 152 ++++++-------------
 src/libthread/mkfile       |   4 +-
 src/libthread/note.c       |   6 +-
 src/libthread/proctab.c    |   2 +-
 src/libthread/ref.c        |   6 +
 src/libthread/rendez.c     |  38 -----
 src/libthread/sched.c      | 355 +++++++++++++++++++++++----------------------
 src/libthread/sleep.c      |  38 +++++
 src/libthread/texec.c      |  11 +-
 src/libthread/threadimpl.h | 110 +++++++-------
 src/libthread/ucontext.c   |  13 +-
 20 files changed, 500 insertions(+), 615 deletions(-)
 delete mode 100644 src/libthread/exec.c
 delete mode 100644 src/libthread/rendez.c
 create mode 100644 src/libthread/sleep.c

(limited to 'src')

diff --git a/src/libthread/chanprint.c b/src/libthread/chanprint.c
index af9e8103..781c6f6f 100644
--- a/src/libthread/chanprint.c
+++ b/src/libthread/chanprint.c
@@ -1,4 +1,6 @@
-#include "threadimpl.h"
+#include <u.h>
+#include <libc.h>
+#include <thread.h>
 
 int
 chanprint(Channel *c, char *fmt, ...)
diff --git a/src/libthread/create.c b/src/libthread/create.c
index 5dee4c48..290c52a8 100644
--- a/src/libthread/create.c
+++ b/src/libthread/create.c
@@ -1,45 +1,46 @@
 #include "threadimpl.h"
 
-Pqueue _threadpq;
-int _threadprocs;
-int __pthread_nonstandard_stacks;
+Pqueue _threadpq;	/* list of all procs */
+int _threadnprocs;	/* count of procs */
 
-static int nextID(void);
+static int newthreadid(void);
+static int newprocid(void);
 
 /*
  * Create and initialize a new Thread structure attached to a given proc.
  */
-void
-_stackfree(void *v)
-{
-	free(v);
-}
-
-static int
-newthread(Proc *p, void (*f)(void *arg), void *arg, uint stacksize, char *name, int grp)
+int
+_newthread(Proc *p, void (*f)(void *arg), void *arg, uint stacksize, 
+	char *name, int grp)
 {
 	int id;
 	Thread *t;
-	char *s;
 
-	__pthread_nonstandard_stacks = 1;
-	if(stacksize < 32)
-		sysfatal("bad stacksize %d", stacksize);
 	t = _threadmalloc(sizeof(Thread), 1);
-	t->lastfd = -1;
-	s = _threadmalloc(stacksize, 0);
-	t->stk = (uchar*)s;
-	t->stksize = stacksize;
-	_threaddebugmemset(s, 0xFE, stacksize);
-	_threadinitstack(t, f, arg);
 	t->proc = p;
 	t->grp = grp;
+	t->id = id = newthreadid();
 	if(name)
-		t->cmdname = strdup(name);
-	t->id = nextID();
-	id = t->id;
-	t->next = (Thread*)~0;
-	_threaddebug(DBGSCHED, "create thread %d.%d name %s", p->pid, t->id, name);
+		t->name = strdup(name);
+	_threaddebug(DBGSCHED, "create thread %d.%d name %s", p->id, id, name);
+
+	/*
+	 * Allocate and clear stack.
+	 */
+	if(stacksize < 1024)
+		sysfatal("bad stacksize %d", stacksize);
+	t->stk = _threadmalloc(stacksize, 0);
+	t->stksize = stacksize;
+	_threaddebugmemset(t->stk, 0xFE, stacksize);
+
+	/*
+	 * Set up t->context to call f(arg).
+	 */
+	_threadinitstack(t, f, arg);
+
+	/*
+	 * Add thread to proc.
+	 */
 	lock(&p->lock);
 	p->nthreads++;
 	if(p->threads.head == nil)
@@ -49,120 +50,134 @@ newthread(Proc *p, void (*f)(void *arg), void *arg, uint stacksize, char *name,
 		t->prevt->nextt = t;
 	}
 	p->threads.tail = t;
+	t->next = (Thread*)~0;
+
+	/*
+	 * Mark thread as ready to run.
+	 */
 	t->state = Ready;
 	_threadready(t);
 	unlock(&p->lock);
+
 	return id;
 }
 
-static int
-nextID(void)
-{
-	static Lock l;
-	static int id;
-	int i;
-
-	lock(&l);
-	i = ++id;
-	unlock(&l);
-	return i;
-}
-	
-int
-procrfork(void (*f)(void *), void *arg, uint stacksize, int rforkflag)
+/* 
+ * Free a Thread structure.
+ */
+void
+_threadfree(Thread *t)
 {
-	Proc *p;
-	int id;
-
-	p = _threadgetproc();
-	assert(p->newproc == nil);
-	p->newproc = _newproc(f, arg, stacksize, nil, p->thread->grp, rforkflag);
-	id = p->newproc->threads.head->id;
-	_sched();
-	return id;
+	free(t->stk);
+	free(t->name);
+	free(t);
 }
 
-int
-proccreate(void (*f)(void*), void *arg, uint stacksize)
+/*
+ * Create and initialize a new Proc structure with a single Thread
+ * running inside it.  Add the Proc to the global process list.
+ */
+Proc*
+_newproc(void)
 {
 	Proc *p;
 
-	p = _threadgetproc();
-	if(p->idle){
-		fprint(2, "cannot create procs once there is an idle thread\n");
-		werrstr("cannot create procs once there is an idle thread");
-		return -1;
-	}
-	return procrfork(f, arg, stacksize, 0);
+	/*
+	 * Allocate.
+	 */
+	p = _threadmalloc(sizeof *p, 1);
+	p->id = newprocid();
+	
+	/*
+	 * Add to list.  Record if we're now multiprocess.
+	 */
+	lock(&_threadpq.lock);
+	if(_threadpq.head == nil)
+		_threadpq.head = p;
+	else
+		*_threadpq.tail = p;
+	_threadpq.tail = &p->next;
+	if(_threadnprocs == 1)
+		_threadmultiproc();
+	_threadnprocs++;
+	unlock(&_threadpq.lock);
+
+	return p;
 }
 
-void
-_freeproc(Proc *p)
+/*
+ * Allocate a new thread running f(arg) on a stack of size stacksize.
+ * Return the thread id.  The thread group inherits from the current thread.
+ */
+int
+threadcreate(void (*f)(void*), void *arg, uint stacksize)
 {
-	Thread *t, *nextt;
-
-	for(t = p->threads.head; t; t = nextt){
-		if(t->cmdname)
-			free(t->cmdname);
-		assert(t->stk != nil);
-		_stackfree(t->stk);
-		nextt = t->nextt;
-		free(t);
-	}
-	free(p);
+	return _newthread(_threadgetproc(), f, arg, stacksize, nil, threadgetgrp());
 }
 
 /* 
- * Create a new thread and schedule it to run.
- * The thread grp is inherited from the currently running thread.
+ * Allocate a new idle thread.  Only allowed in a single-proc program.
  */
 int
-threadcreate(void (*f)(void *arg), void *arg, uint stacksize)
+threadcreateidle(void (*f)(void *arg), void *arg, uint stacksize)
 {
-	return newthread(_threadgetproc(), f, arg, stacksize, nil, threadgetgrp());
+	int id;
+
+	assert(_threadnprocs == 1);
+
+	id = threadcreate(f, arg, stacksize);
+	_threaddebug(DBGSCHED, "idle is %d", id);
+	_threadsetidle(id);
+	return id;
 }
 
+/*
+ * Threadcreate, but do it inside a fresh proc.
+ */
 int
-threadcreateidle(void (*f)(void *arg), void *arg, uint stacksize)
+proccreate(void (*f)(void*), void *arg, uint stacksize)
 {
 	int id;
+	Proc *p, *np;
 
-	if(_threadprocs!=1){
-		fprint(2, "cannot have idle thread in multi-proc program\n");
-		werrstr("cannot have idle thread in multi-proc program");
-		return -1;
-	}
-	id = newthread(_threadgetproc(), f, arg, stacksize, nil, threadgetgrp());
-	_threaddebug(DBGSCHED, "idle is %d", id);
-	_threadidle();
+	p = _threadgetproc();
+	np = _newproc();
+	p->newproc = np;
+	p->schedfn = _threadstartproc;
+	id = _newthread(np, f, arg, stacksize, nil, p->thread->grp);
+	_sched();	/* call into scheduler to create proc XXX */
 	return id;
 }
 
 /*
- * Create and initialize a new Proc structure with a single Thread
- * running inside it.  Add the Proc to the global process list.
+ * Allocate a new thread id.
  */
-Proc*
-_newproc(void (*f)(void *arg), void *arg, uint stacksize, char *name, int grp, int rforkflag)
+static int
+newthreadid(void)
 {
-	Proc *p;
+	static Lock l;
+	static int id;
+	int i;
 
-	p = _threadmalloc(sizeof *p, 1);
-	p->pid = -1;
-	p->rforkflag = rforkflag;
-	newthread(p, f, arg, stacksize, name, grp);
+	lock(&l);
+	i = ++id;
+	unlock(&l);
+	return i;
+}
 
-	lock(&_threadpq.lock);
-	if(_threadpq.head == nil)
-		_threadpq.head = p;
-	else
-		*_threadpq.tail = p;
-	_threadpq.tail = &p->next;
+/*
+ * Allocate a new proc id.
+ */
+static int
+newprocid(void)
+{
+	static Lock l;
+	static int id;
+	int i;
 
-	if(_threadprocs == 1)
-		_threadmultiproc();
-	_threadprocs++;
-	unlock(&_threadpq.lock);
-	return p;
+	lock(&l);
+	i = ++id;
+	unlock(&l);
+	return i;
 }
 
diff --git a/src/libthread/debug.c b/src/libthread/debug.c
index 63e2e1b5..14b47c00 100644
--- a/src/libthread/debug.c
+++ b/src/libthread/debug.c
@@ -19,9 +19,9 @@ __threaddebug(ulong flag, char *fmt, ...)
 	if(p==nil)
 		fmtprint(&f, "noproc ");
 	else if(p->thread)
-		fmtprint(&f, "%d.%d ", p->pid, p->thread->id);
+		fmtprint(&f, "%d.%d ", p->id, p->thread->id);
 	else
-		fmtprint(&f, "%d._ ", p->pid);
+		fmtprint(&f, "%d._ ", p->id);
 
 	va_start(arg, fmt);
 	fmtvprint(&f, fmt, arg);
diff --git a/src/libthread/exec-unix.c b/src/libthread/exec-unix.c
index 3d4dfcac..91639bbb 100644
--- a/src/libthread/exec-unix.c
+++ b/src/libthread/exec-unix.c
@@ -10,9 +10,20 @@ _threadexec(Channel *pidc, int fd[3], char *prog, char *args[], int freeargs)
 	int pfd[2];
 	int n, pid;
 	char exitstr[ERRMAX];
+	static int firstexec = 1;
+	static Lock lk;
 
 	_threaddebug(DBGEXEC, "threadexec %s", prog);
-	
+
+	if(firstexec){
+		lock(&lk);
+		if(firstexec){
+			firstexec = 0;
+			_threadfirstexec();
+		}
+		unlock(&lk);
+	}
+
 	/*
 	 * We want threadexec to behave like exec; if exec succeeds,
 	 * never return, and if it fails, return with errstr set.
@@ -41,6 +52,7 @@ _threadexec(Channel *pidc, int fd[3], char *prog, char *args[], int freeargs)
 		efork(fd, pfd, prog, args);
 		_exit(0);
 	default:
+		_threadafterexec();
 		if(freeargs)
 			free(args);
 		break;
diff --git a/src/libthread/exec.c b/src/libthread/exec.c
deleted file mode 100644
index 0fb68111..00000000
--- a/src/libthread/exec.c
+++ /dev/null
@@ -1,82 +0,0 @@
-#include "threadimpl.h"
-
-#define PIPEMNT	"/mnt/temp"
-
-void
-procexec(Channel *pidc, int fd[3], char *prog, char *args[])
-{
-	int n;
-	Proc *p;
-	Thread *t;
-
-	_threaddebug(DBGEXEC, "procexec %s", prog);
-	/* must be only thread in proc */
-	p = _threadgetproc();
-	t = p->thread;
-	if(p->threads.head != t || p->threads.head->nextt != nil){
-		werrstr("not only thread in proc");
-	Bad:
-		if(pidc)
-			sendul(pidc, ~0);
-		return;
-	}
-
-	/*
-	 * We want procexec to behave like exec; if exec succeeds,
-	 * never return, and if it fails, return with errstr set.
-	 * Unfortunately, the exec happens in another proc since
-	 * we have to wait for the exec'ed process to finish.
-	 * To provide the semantics, we open a pipe with the 
-	 * write end close-on-exec and hand it to the proc that
-	 * is doing the exec.  If the exec succeeds, the pipe will
-	 * close so that our read below fails.  If the exec fails,
-	 * then the proc doing the exec sends the errstr down the
-	 * pipe to us.
-	 */
-	if(bind("#|", PIPEMNT, MREPL) < 0)
-		goto Bad;
-	if((p->exec.fd[0] = open(PIPEMNT "/data", OREAD)) < 0){
-		unmount(nil, PIPEMNT);
-		goto Bad;
-	}
-	if((p->exec.fd[1] = open(PIPEMNT "/data1", OWRITE|OCEXEC)) < 0){
-		close(p->exec.fd[0]);
-		unmount(nil, PIPEMNT);
-		goto Bad;
-	}
-	unmount(nil, PIPEMNT);
-
-	/* exec in parallel via the scheduler */
-	assert(p->needexec==0);
-	p->exec.prog = prog;
-	p->exec.args = args;
-	p->exec.stdfd = fd;
-	p->needexec = 1;
-	_sched();
-
-	close(p->exec.fd[1]);
-	if((n = read(p->exec.fd[0], p->exitstr, ERRMAX-1)) > 0){	/* exec failed */
-		p->exitstr[n] = '\0';
-		errstr(p->exitstr, ERRMAX);
-		close(p->exec.fd[0]);
-		goto Bad;
-	}
-	close(p->exec.fd[0]);
-	close(fd[0]);
-	if(fd[1] != fd[0])
-		close(fd[1]);
-	if(fd[2] != fd[1] && fd[2] != fd[0])
-		close(fd[2]);
-	if(pidc)
-		sendul(pidc, t->ret);
-
-	/* wait for exec'ed program, then exit */
-	_schedexecwait();
-}
-
-void
-procexecl(Channel *pidc, int fd[3], char *f, ...)
-{
-	procexec(pidc, fd, f, &f+1);
-}
-
diff --git a/src/libthread/exit.c b/src/libthread/exit.c
index f3d4bb8e..79aa7c7f 100644
--- a/src/libthread/exit.c
+++ b/src/libthread/exit.c
@@ -26,42 +26,13 @@ threadexits(char *exitstr)
 void
 threadexitsall(char *exitstr)
 {
-	Proc *p;
-	int *pid;
-	int i, npid, mypid;
-
 	_threaddebug(DBGSCHED, "threadexitsall %s", exitstr);
 	if(exitstr == nil)
 		exitstr = "";
 	_threadexitsallstatus = exitstr;
 	_threaddebug(DBGSCHED, "_threadexitsallstatus set to %p", _threadexitsallstatus);
-	mypid = _threadgetpid();
-
-	/*
-	 * signal others.
-	 * copying all the pids first avoids other thread's
-	 * teardown procedures getting in the way.
-	 */
-	lock(&_threadpq.lock);
-	npid = 0;
-	for(p=_threadpq.head; p; p=p->next)
-		npid++;
-	pid = _threadmalloc(npid*sizeof(pid[0]), 0);
-	npid = 0;
-	for(p = _threadpq.head; p; p=p->next)
-		pid[npid++] = p->pid;
-	unlock(&_threadpq.lock);
-	for(i=0; i<npid; i++){
-		_threaddebug(DBGSCHED, "threadexitsall kill %d", pid[i]);
-		if(pid[i]==0 || pid[i]==-1)
-			fprint(2, "bad pid in threadexitsall: %d\n", pid[i]);
-		else if(pid[i] != mypid){
-			kill(pid[i], SIGTERM);
-		}
-	}
-
 	/* leave */
-	exits(0);
+	_threadexitallproc(exitstr);
 }
 
 Channel*
diff --git a/src/libthread/id.c b/src/libthread/id.c
index d32a92f2..a6d5222f 100644
--- a/src/libthread/id.c
+++ b/src/libthread/id.c
@@ -60,10 +60,10 @@ threadsetname(char *fmt, ...)
 
 	p = _threadgetproc();
 	t = p->thread;
-	if (t->cmdname)
-		free(t->cmdname);
+	if(t->name)
+		free(t->name);
 	va_start(arg, fmt);
-	t->cmdname = vsmprint(fmt, arg);
+	t->name = vsmprint(fmt, arg);
 	va_end(arg);
 
 /* Plan 9 only 
@@ -85,7 +85,7 @@ threadsetname(char *fmt, ...)
 char*
 threadgetname(void)
 {
-	return _threadgetproc()->thread->cmdname;
+	return _threadgetproc()->thread->name;
 }
 
 void**
diff --git a/src/libthread/iocall.c b/src/libthread/iocall.c
index 0577f8a0..e359c4d5 100644
--- a/src/libthread/iocall.c
+++ b/src/libthread/iocall.c
@@ -1,4 +1,7 @@
-#include "threadimpl.h"
+#include <u.h>
+#include <libc.h>
+#include <thread.h>
+#include "ioproc.h"
 
 long
 iocall(Ioproc *io, long (*op)(va_list*), ...)
diff --git a/src/libthread/ioproc.c b/src/libthread/ioproc.c
index 2b2a6025..4e4c32a8 100644
--- a/src/libthread/ioproc.c
+++ b/src/libthread/ioproc.c
@@ -1,4 +1,7 @@
-#include "threadimpl.h"
+#include <u.h>
+#include <libc.h>
+#include <thread.h>
+#include "ioproc.h"
 
 enum
 {
diff --git a/src/libthread/main.c b/src/libthread/main.c
index 8cdd8ca3..83ee177c 100644
--- a/src/libthread/main.c
+++ b/src/libthread/main.c
@@ -1,135 +1,79 @@
-#include <u.h>
-#include <signal.h>
+/*
+ * Thread library.  
+ */
+
 #include "threadimpl.h"
 
 typedef struct Mainarg Mainarg;
 struct Mainarg
 {
-	int	argc;
-	char	**argv;
+	int argc;
+	char **argv;
 };
 
-int	mainstacksize;
-int	_threadnotefd;
-int	_threadpasserpid;
-static void mainlauncher(void*);
+int mainstacksize;
 extern void (*_sysfatal)(char*, va_list);
 
-void
-_threadstatus(int x)
-{
-	USED(x);
-	threadstatus();
-}
-
-void
-_threaddie(int x)
-{
-	extern char *_threadexitsallstatus;
-	USED(x);
-
-	if(_threadexitsallstatus)
-		_exits(_threadexitsallstatus);
-}
-
-int
-main(int argc, char **argv)
-{
-	Mainarg *a;
-	Proc *p;
-
-//_threaddebuglevel = (DBGSCHED|DBGCHAN|DBGREND)^~0;
-	_systhreadinit();
-	_qlockinit(_threadsleep, _threadwakeup);
-	_sysfatal = _threadsysfatal;
-	notify(_threadnote);
-	if(mainstacksize == 0)
-		mainstacksize = 32*1024;
-
-	a = _threadmalloc(sizeof *a, 1);
-	a->argc = argc;
-	a->argv = argv;
-	p = _newproc(mainlauncher, a, mainstacksize, "threadmain", 0, 0);
-	_scheduler(p);
-	abort();	/* not reached */
-	return 0;
-}
-
 static void
 mainlauncher(void *arg)
 {
 	Mainarg *a;
 
 	a = arg;
+	_threadmaininit();
 	threadmain(a->argc, a->argv);
 	threadexits("threadmain");
 }
 
-void
-_threadsignal(void)
-{
-}
-
-void
-_threadsignalpasser(void)
-{
-}
-
 int
-_schedfork(Proc *p)
+main(int argc, char **argv)
 {
-	int pid;
-	lock(&p->lock);
-	pid = ffork(RFMEM|RFNOWAIT, _scheduler, p);
-	p->pid = pid;
-	unlock(&p->lock);
-	return pid;
-	
-}
+	Mainarg a;
+	Proc *p;
 
-void
-_schedexit(Proc *p)
-{
-	char ex[ERRMAX];
-	Proc **l;
+	/*
+	 * XXX Do daemonize hack here.
+	 */
+
+	/*
+	 * Instruct QLock et al. to use our scheduling functions
+	 * so that they can operate at the thread level.
+	 */
+	_qlockinit(_threadsleep, _threadwakeup);
 
-	lock(&_threadpq.lock);
-	for(l=&_threadpq.head; *l; l=&(*l)->next){
-		if(*l == p){
-			*l = p->next;
-			if(*l == nil)
-				_threadpq.tail = l;
-			break;
-		}
-	}
-	_threadprocs--;
-	unlock(&_threadpq.lock);
+	/*
+	 * Install our own _threadsysfatal which takes down
+	 * the whole conglomeration of procs.
+	 */
+	_sysfatal = _threadsysfatal;
 
-	strncpy(ex, p->exitstr, sizeof ex);
-	ex[sizeof ex-1] = '\0';
-	free(p);
-	_exits(ex);
-}
+	/*
+	 * XXX Install our own jump handler.
+	 */
 
-int
-nrand(int n)
-{
-	return random()%n;
-}
+	/*
+	 * Install our own signal handlers.
+	 */
+	notify(_threadnote);
 
-void
-_systhreadinit(void)
-{
+	/*
+	 * Construct the initial proc running mainlauncher(&a).
+	 */
+	if(mainstacksize == 0)
+		mainstacksize = 32*1024;
+	a.argc = argc;
+	a.argv = argv;
+	p = _newproc();
+	_newthread(p, mainlauncher, &a, mainstacksize, "threadmain", 0);
+	_threadscheduler(p);
+	abort();	/* not reached */
+	return 0;
 }
 
+/*
+ * No-op function here so that sched.o drags in main.o.
+ */
 void
-threadstats(void)
+_threadlinkmain(void)
 {
-	extern int _threadnrendez, _threadhighnrendez,
-		_threadnalt, _threadhighnentry;
-	fprint(2, "*** THREAD LIBRARY STATS ***\n");
-	fprint(2, "nrendez %d high simultaneous %d\n", 
-		_threadnrendez, _threadhighnrendez);
-	fprint(2, "nalt %d high simultaneous entry %d\n",
-		_threadnalt, _threadhighnentry);
 }
diff --git a/src/libthread/mkfile b/src/libthread/mkfile
index abff1629..ede391da 100644
--- a/src/libthread/mkfile
+++ b/src/libthread/mkfile
@@ -28,11 +28,11 @@ OFILES=\
 	memset.$O\
 	memsetd.$O\
 	note.$O\
-	proctab.$O\
+	pthread.$O\
 	read9pmsg.$O\
 	ref.$O\
-	rendez.$O\
 	sched.$O\
+	sleep.$O\
 
 HFILES=\
 	$PLAN9/include/thread.h\
diff --git a/src/libthread/note.c b/src/libthread/note.c
index 241c16ff..60742aad 100644
--- a/src/libthread/note.c
+++ b/src/libthread/note.c
@@ -65,6 +65,8 @@ delayednotes(Proc *p, void *v)
 			}
 			if(i==NFN){
 				_threaddebug(DBGNOTE, "Unhandled note %s, proc %p\n", n->s, p);
+				if(strcmp(n->s, "sys: child") == 0)
+					noted(NCONT);
 				fprint(2, "unhandled note %s, pid %d\n", n->s, p->pid);
 				if(v != nil)
 					noted(NDFLT);
@@ -85,7 +87,9 @@ _threadnote(void *v, char *s)
 	Note *n;
 
 	_threaddebug(DBGNOTE, "Got note %s", s);
-	if(strncmp(s, "sys:", 4) == 0 && strcmp(s, "sys: write on closed pipe") != 0)
+	if(strncmp(s, "sys:", 4) == 0
+	&& strcmp(s, "sys: write on closed pipe") != 0
+	&& strcmp(s, "sys: child") != 0)
 		noted(NDFLT);
 
 //	if(_threadexitsallstatus){
diff --git a/src/libthread/proctab.c b/src/libthread/proctab.c
index ec28d676..b8dd2097 100644
--- a/src/libthread/proctab.c
+++ b/src/libthread/proctab.c
@@ -46,7 +46,7 @@ __threadgetproc(int rm)
 	if(!multi)
 		return theproc;
 
-	pid = _threadgetpid();
+	pid = getpid();
 
 	lock(&ptablock);
 	h = ((unsigned)pid)%PTABHASH;
diff --git a/src/libthread/ref.c b/src/libthread/ref.c
index 8f50fd5f..a3b2cbae 100644
--- a/src/libthread/ref.c
+++ b/src/libthread/ref.c
@@ -1,3 +1,9 @@
+/*
+ * Atomic reference counts - used by applications.
+ *
+ * We use locks to avoid the assembly of the Plan 9 versions.
+ */
+
 #include "threadimpl.h"
 
 void
diff --git a/src/libthread/rendez.c b/src/libthread/rendez.c
deleted file mode 100644
index 4451fa4d..00000000
--- a/src/libthread/rendez.c
+++ /dev/null
@@ -1,38 +0,0 @@
-#include "threadimpl.h"
-
-int _threadhighnrendez;
-int _threadnrendez;
-
-void
-_threadsleep(_Procrend *r)
-{
-	Thread *t;
-
-	t = _threadgetproc()->thread;
-	r->arg = t;
-	t->nextstate = Rendezvous;
-	t->inrendez = 1;
-	unlock(r->l);
-	_sched();
-	t->inrendez = 0;
-	lock(r->l);
-}
-
-void
-_threadwakeup(_Procrend *r)
-{
-	Thread *t;
-
-	t = r->arg;
-	while(t->state == Running)
-		sleep(0);
-	lock(&t->proc->lock);
-	if(t->state == Dead){
-		unlock(&t->proc->lock);
-		return;
-	}
-	assert(t->state == Rendezvous && t->inrendez);
-	t->state = Ready;
-	_threadready(t);
-	unlock(&t->proc->lock);
-}
diff --git a/src/libthread/sched.c b/src/libthread/sched.c
index 7f7b6daa..3fb2ff20 100644
--- a/src/libthread/sched.c
+++ b/src/libthread/sched.c
@@ -1,76 +1,59 @@
-#include <u.h>
-#include <signal.h>
-#include <errno.h>
+/*
+ * Thread scheduler.
+ */
 #include "threadimpl.h"
 
-static Thread	*runthread(Proc*);
-
-static char *_psstate[] = {
-	"Dead",
-	"Running",
-	"Ready",
-	"Rendezvous",
-};
-
-static char*
-psstate(int s)
-{
-	if(s < 0 || s >= nelem(_psstate))
-		return "unknown";
-	return _psstate[s];
-}
-
-void
-needstack(int howmuch)
-{
-	Proc *p;
-	Thread *t;
-
-	p = _threadgetproc();
-	if(p == nil || (t=p->thread) == nil)
-		return;
-	if((ulong)&howmuch < (ulong)t->stk+howmuch){	/* stack overflow waiting to happen */
-		fprint(2, "stack overflow: stack at 0x%lux, limit at 0x%lux, need 0x%lux\n", (ulong)&p, (ulong)t->stk, howmuch);
-		abort();
-	}
-}
+static Thread *runthread(Proc*);
+static void schedexit(Proc*);
 
+/*
+ * Main scheduling loop.
+ */
 void
-_scheduler(void *arg)
+_threadscheduler(void *arg)
 {
 	Proc *p;
 	Thread *t;
 
 	p = arg;
-	lock(&p->lock);
-	p->pid = _threadgetpid();
-	_threadsetproc(p);
+
+	_threadlinkmain();
+	_threadinitproc(p);
 
 	for(;;){
+		/* 
+		 * Clean up zombie children.
+		 */
+		_threadwaitkids(p);
+
+		/*
+		 * Find next thread to run.
+		 */
+		_threaddebug(DBGSCHED, "runthread");
 		t = runthread(p);
-		if(t == nil){
-			_threaddebug(DBGSCHED, "all threads gone; exiting");
-			_threaddelproc();
-			_schedexit(p);
-		}
-		_threaddebug(DBGSCHED, "running %d.%d", t->proc->pid, t->id);
-		p->thread = t;
-		if(t->moribund){
-			_threaddebug(DBGSCHED, "%d.%d marked to die");
-			goto Moribund;
+		if(t == nil)
+			schedexit(p);
+	
+		/*
+		 * If it's ready, run it (might instead be marked to die).
+		 */
+		lock(&p->lock);
+		if(t->state == Ready){
+			_threaddebug(DBGSCHED, "running %d.%d", p->id, t->id);
+			t->state = Running;
+			t->nextstate = Ready;
+			p->thread = t;
+			unlock(&p->lock);
+			_swaplabel(&p->context, &t->context);
+			lock(&p->lock);
+			p->thread = nil;
 		}
-		t->state = Running;
-		t->nextstate = Ready;
-		unlock(&p->lock);
 
-		_swaplabel(&p->sched, &t->sched);
-
-		lock(&p->lock);
-		p->thread = nil;
+		/*
+		 * If thread needs to die, kill it.
+		 */
 		if(t->moribund){
-		Moribund:
-			if(t->moribund != 1)
-				fprint(2, "moribund %d\n", t->moribund);
+			_threaddebug(DBGSCHED, "moribund %d.%d", p->id, t->id);
 			assert(t->moribund == 1);
 			t->state = Dead;
 			if(t->prevt)
@@ -82,40 +65,37 @@ _scheduler(void *arg)
 			else
 				p->threads.tail = t->prevt;
 			unlock(&p->lock);
-			if(t->inrendez){
-				abort();
-			//	_threadflagrendez(t);
-			//	_threadbreakrendez();
-			}
-			_stackfree(t->stk);
-			free(t->cmdname);
-			free(t);	/* XXX how do we know there are no references? */
+			_threadfree(t);
 			p->nthreads--;
 			t = nil;
-			lock(&p->lock);
 			continue;
 		}
-/*
-		if(p->needexec){
-			t->ret = _schedexec(&p->exec);
-			p->needexec = 0;
-		}
-*/
-		if(p->newproc){
-			t->ret = _schedfork(p->newproc);
-			if(t->ret < 0){
-//fprint(2, "_schedfork: %r\n");
-				abort();
-			}
-			p->newproc = nil;
+		unlock(&p->lock);
+
+		/*
+		 * If there is a request to run a function on the 
+		 * scheduling stack, do so.
+		 */
+		if(p->schedfn){
+			_threaddebug(DBGSCHED, "schedfn");
+			p->schedfn(p);
+			p->schedfn = nil;
+			_threaddebug(DBGSCHED, "schedfn ended");
 		}
+
+		/*
+		 * Move the thread along.
+		 */
 		t->state = t->nextstate;
+		_threaddebug(DBGSCHED, "moveon %d.%d", p->id, t->id);
 		if(t->state == Ready)
 			_threadready(t);
-		unlock(&p->lock);
 	}
 }
 
+/*
+ * Called by thread to give up control of processor to scheduler.
+ */
 int
 _sched(void)
 {
@@ -125,166 +105,195 @@ _sched(void)
 	p = _threadgetproc();
 	t = p->thread;
 	assert(t != nil);
-	_swaplabel(&t->sched, &p->sched);
+	_swaplabel(&t->context, &p->context);
 	return p->nsched++;
 }
 
+/*
+ * Called by thread to yield the processor to other threads.
+ * Returns number of other threads run between call and return.
+ */
+int
+yield(void)
+{
+	Proc *p;
+	int nsched;
+
+	p = _threadgetproc();
+	nsched = p->nsched;
+	return _sched() - nsched;
+}
+
+/*
+ * Choose the next thread to run.
+ */
 static Thread*
 runthread(Proc *p)
 {
-	Channel *c;
 	Thread *t;
 	Tqueue *q;
-	Waitmsg *w;
-	int e, sent;
 
+	/*
+	 * No threads left?
+	 */
 	if(p->nthreads==0 || (p->nthreads==1 && p->idle))
 		return nil;
-	q = &p->ready;
-relock:
+
 	lock(&p->readylock);
-	if(p->nsched%128 == 0){
-		/* clean up children */
-		e = errno;
-		if((c = _threadwaitchan) != nil){
-			if(c->n <= c->s){
-				sent = 0;
-				for(;;){
-					if((w = p->waitmsg) != nil)
-						p->waitmsg = nil;
-					else
-						w = waitnohang();
-					if(w == nil)
-						break;
-					if(sent == 0){
-						unlock(&p->readylock);
-						sent = 1;
-					}
-					if(nbsendp(c, w) != 1)
-						break;
-				}
-				p->waitmsg = w;
-				if(sent)
-					goto relock;
-			}
-		}else{
-			while((w = waitnohang()) != nil)
-				free(w);
-		}
-		errno = e;
-	}
+	q = &p->ready;
 	if(q->head == nil){
+		/*
+		 * Is this a single-process program with an idle thread?
+		 */
 		if(p->idle){
-			if(p->idle->state != Ready){
-				fprint(2, "everyone is asleep\n");
-				exits("everyone is asleep");
-			}
+			/*
+			 * The idle thread had better be ready!
+			 */
+			if(p->idle->state != Ready)
+				sysfatal("all threads are asleep");
+
+			/*
+			 * Run the idle thread.
+			 */
 			unlock(&p->readylock);
 			_threaddebug(DBGSCHED, "running idle thread", p->nthreads);
 			return p->idle;
 		}
 
-		_threaddebug(DBGSCHED, "sleeping for more work (%d threads)", p->nthreads);
+		/*
+		 * Wait until one of our threads is readied (by another proc!).
+		 */
 		q->asleep = 1;
 		p->rend.l = &p->readylock;
 		_procsleep(&p->rend);
+
+		/*
+		 * Maybe we were awakened to exit?
+		 */
 		if(_threadexitsallstatus)
 			_exits(_threadexitsallstatus);
+
+		assert(q->head != nil);
 	}
+
 	t = q->head;
 	q->head = t->next;
 	unlock(&p->readylock);
-	return t;
-}
 
-long
-threadstack(void)
-{
-	Proc *p;
-	Thread *t;
-
-	p = _threadgetproc();
-	t = p->thread;
-	return (ulong)&p - (ulong)t->stk;
+	return t;
 }
 
+/*
+ * Add a newly-ready thread to its proc's run queue.
+ */
 void
 _threadready(Thread *t)
 {
 	Tqueue *q;
 
+	/*
+	 * The idle thread does not go on the run queue.
+	 */
 	if(t == t->proc->idle){
 		_threaddebug(DBGSCHED, "idle thread is ready");
 		return;
 	}
 
 	assert(t->state == Ready);
-	_threaddebug(DBGSCHED, "readying %d.%d", t->proc->pid, t->id);
+	_threaddebug(DBGSCHED, "readying %d.%d", t->proc->id, t->id);
+
+	/*
+	 * Add thread to run queue.
+	 */
 	q = &t->proc->ready;
 	lock(&t->proc->readylock);
+
 	t->next = nil;
-	if(q->head==nil)
+	if(q->head == nil)
 		q->head = t;
 	else
 		q->tail->next = t;
 	q->tail = t;
+
+	/*
+	 * Wake proc scheduler if it is sleeping.
+	 */
 	if(q->asleep){
 		assert(q->asleep == 1);
 		q->asleep = 0;
-		/* lock passes to runthread */
 		_procwakeup(&t->proc->rend);
 	}
 	unlock(&t->proc->readylock);
-	if(_threadexitsallstatus)
-		_exits(_threadexitsallstatus);
 }
 
+/*
+ * Mark the given thread as the idle thread.
+ * Since the idle thread was just created, it is sitting
+ * somewhere on the ready queue.
+ */
 void
-_threadidle(void)
+_threadsetidle(int id)
 {
 	Tqueue *q;
-	Thread *t, *idle;
+	Thread *t, **l, *last;
 	Proc *p;
 
 	p = _threadgetproc();
-	q = &p->ready;
+
 	lock(&p->readylock);
-	assert(q->tail);
-	idle = q->tail;
-	if(q->head == idle){
-		q->head = nil;
-		q->tail = nil;
-	}else{
-		for(t=q->head; t->next!=q->tail; t=t->next)
-			;
-		t->next = nil;
-		q->tail = t;
-	}
-	p->idle = idle;
-	_threaddebug(DBGSCHED, "p->idle is %d\n", idle->id);
-	unlock(&p->readylock);
-}
 
-int
-yield(void)
-{
-	Proc *p;
-	int nsched;
+	/*
+	 * Find thread on ready queue.
+	 */
+	q = &p->ready;
+	for(l=&q->head, last=nil; (t=*l) != nil; l=&t->next, last=t)
+		if(t->id == id)
+			break;
+	assert(t != nil);
 
-	p = _threadgetproc();
-	nsched = p->nsched;
-	return _sched() - nsched;
+	/* 
+	 * Remove it from ready queue.
+	 */
+	*l = t->next;
+	if(t == q->head)
+		q->head = t->next;
+	if(t->next == nil)
+		q->tail = last;
+
+	/*
+	 * Set as idle thread.
+	 */
+	p->idle = t;
+	_threaddebug(DBGSCHED, "p->idle is %d\n", t->id);
+	unlock(&p->readylock);
 }
 
-void
-threadstatus(void)
+static void
+schedexit(Proc *p)
 {
-	Proc *p;
-	Thread *t;
+	char ex[ERRMAX];
+	int n;
+	Proc **l;
 
-	p = _threadgetproc();
-	for(t=p->threads.head; t; t=t->nextt)
-		fprint(2, "[%3d] %s userpc=%lux\n",
-			t->id, psstate(t->state), t->userpc);
+	_threaddebug(DBGSCHED, "exiting proc %d", p->id);
+	lock(&_threadpq.lock);
+	for(l=&_threadpq.head; *l; l=&(*l)->next){
+		if(*l == p){
+			*l = p->next;
+			if(*l == nil)
+				_threadpq.tail = l;
+			break;
+		}
+	}
+	n = --_threadnprocs;
+	unlock(&_threadpq.lock);
+
+	strncpy(ex, p->exitstr, sizeof ex);
+	ex[sizeof ex-1] = '\0';
+	free(p);
+	if(n == 0)
+		_threadexitallproc(ex);
+	else
+		_threadexitproc(ex);
 }
-	
+
diff --git a/src/libthread/sleep.c b/src/libthread/sleep.c
new file mode 100644
index 00000000..d6c4dac4
--- /dev/null
+++ b/src/libthread/sleep.c
@@ -0,0 +1,38 @@
+#include "threadimpl.h"
+
+int _threadhighnrendez;
+int _threadnrendez;
+
+void
+_threadsleep(_Procrend *r)
+{
+	Thread *t;
+
+	t = _threadgetproc()->thread;
+	r->arg = t;
+	t->nextstate = Rendezvous;
+	t->asleep = 1;
+	unlock(r->l);
+	_sched();
+	t->asleep = 0;
+	lock(r->l);
+}
+
+void
+_threadwakeup(_Procrend *r)
+{
+	Thread *t;
+
+	t = r->arg;
+	while(t->state == Running)
+		sleep(0);
+	lock(&t->proc->lock);
+	if(t->state == Dead){
+		unlock(&t->proc->lock);
+		return;
+	}
+	assert(t->state == Rendezvous && t->asleep);
+	t->state = Ready;
+	_threadready(t);
+	unlock(&t->proc->lock);
+}
diff --git a/src/libthread/texec.c b/src/libthread/texec.c
index 87c3f77b..bcfabee6 100644
--- a/src/libthread/texec.c
+++ b/src/libthread/texec.c
@@ -5,11 +5,16 @@ extern int _threaddebuglevel;
 void
 doexec(void *v)
 {
+	int fd[3];
 	char **argv = v;
 
-print("doexec\n");
-	procexec(nil, argv[0], argv);
+	fd[0] = dup(0, -1);
+	fd[1] = dup(1, -1);
+	fd[2] = dup(2, -1);
+	threadexec(nil, fd, argv[0], argv);
+	print("exec failed: %r\n");
 	sendp(threadwaitchan(), nil);
+	threadexits(nil);
 }
 
 void
@@ -28,7 +33,7 @@ threadmain(int argc, char **argv)
 	proccreate(doexec, argv, 8192);
 	w = recvp(c);
 	if(w == nil)
-		print("exec failed: %r\n");
+		print("exec/recvp failed: %r\n");
 	else
 		print("%d %lud %lud %lud %s\n", w->pid, w->time[0], w->time[1], w->time[2], w->msg);
 	threadexits(nil);
diff --git a/src/libthread/threadimpl.h b/src/libthread/threadimpl.h
index fea309d9..7c9a66bb 100644
--- a/src/libthread/threadimpl.h
+++ b/src/libthread/threadimpl.h
@@ -7,31 +7,28 @@
  *	_threadgetproc()->thread is always a live pointer.
  *	p->threads, p->ready, and _threadrgrp also contain
  * 	live thread pointers.  These may only be consulted
- *	while holding p->lock or _threadrgrp.lock; in procs
- *	other than p, the pointers are only guaranteed to be live
- *	while the lock is still being held.
+ *	while holding p->lock; in procs other than p, the
+ *	pointers are only guaranteed to be live while the lock
+ *	is still being held.
  *
  *	Thread structures can only be freed by the proc
  *	they belong to.  Threads marked with t->inrendez
  * 	need to be extracted from the _threadrgrp before
  *	being freed.
- *
- *	_threadrgrp.lock cannot be acquired while holding p->lock.
  */
 
+#include <u.h>
 #include <assert.h>
-#include <lib9.h>
+#include <libc.h>
 #include <thread.h>
 #include "label.h"
 
 typedef struct Thread	Thread;
-typedef struct Proc	Proc;
+typedef struct Proc		Proc;
 typedef struct Tqueue	Tqueue;
 typedef struct Pqueue	Pqueue;
-typedef struct Rgrp		Rgrp;
 typedef struct Execargs	Execargs;
 
-/* must match list in sched.c */
 typedef enum
 {
 	Dead,
@@ -50,17 +47,9 @@ typedef enum
 
 enum
 {
-	RENDHASH = 10009,
-	Printsize = 2048,
 	NPRIV = 8,
 };
 
-struct Rgrp
-{
-	Lock		lock;
-	Thread	*hash[RENDHASH];
-};
-
 struct Tqueue		/* Thread queue */
 {
 	int		asleep;
@@ -68,27 +57,38 @@ struct Tqueue		/* Thread queue */
 	Thread	*tail;
 };
 
+struct Pqueue {		/* Proc queue */
+	Lock		lock;
+	Proc		*head;
+	Proc		**tail;
+};
+
 struct Thread
 {
 	Lock		lock;			/* protects thread data structure */
-	Label	sched;		/* for context switches */
-	int		id;			/* thread id */
+
+	int		asleep;		/* thread is in _threadsleep */
+	Label	context;		/* for context switches */
 	int 		grp;			/* thread group */
+	int		id;			/* thread id */
 	int		moribund;	/* thread needs to die */
-	State		state;		/* run state */
-	State		nextstate;		/* next run state */
-	uchar	*stk;			/* top of stack (lowest address of stack) */
-	uint		stksize;		/* stack size */
+	char		*name;		/* name of thread */
 	Thread	*next;		/* next on ready queue */
-
-	Proc		*proc;		/* proc of this thread */
 	Thread	*nextt;		/* next on list of threads in this proc */
+	State		nextstate;		/* next run state */
+	Proc		*proc;		/* proc of this thread */
 	Thread	*prevt;		/* prev on list of threads in this proc */
 	int		ret;			/* return value for Exec, Fork */
+	State		state;		/* run state */
+	uchar	*stk;			/* top of stack (lowest address of stack) */
+	uint		stksize;		/* stack size */
+	void*	udata[NPRIV];	/* User per-thread data pointer */
 
-	char		*cmdname;	/* ptr to name of thread */
+	/*
+	 * for debugging only
+	 * (could go away without impacting correct behavior):
+	 */
 
-	int		inrendez;	
 	Channel	*altc;
 	_Procrend	altrend;
 
@@ -96,10 +96,7 @@ struct Thread
 	Alt		*alt;			/* pointer to current alt structure (debugging) */
 	ulong		userpc;
 	Channel	*c;
-	pthread_cond_t cond;
 
-	void*	udata[NPRIV];	/* User per-thread data pointer */
-	int		lastfd;
 };
 
 struct Execargs
@@ -113,12 +110,13 @@ struct Execargs
 struct Proc
 {
 	Lock		lock;
-	Label	sched;		/* for context switches */
-	Proc		*link;		/* in proctab */
-	int		pid;			/* process id */
+
+	Label	context;		/* for context switches */
+	Proc		*link;		/* in ptab */
 	int		splhi;		/* delay notes */
 	Thread	*thread;		/* running thread */
 	Thread	*idle;			/* idle thread */
+	int		id;
 
 	int		needexec;
 	Execargs	exec;		/* exec argument */
@@ -131,13 +129,15 @@ struct Proc
 	Tqueue	ready;		/* Runnable threads */
 	Lock		readylock;
 
-	char		printbuf[Printsize];
 	int		blocked;		/* In a rendezvous */
 	int		pending;		/* delayed note pending */
 	int		nonotes;		/*  delay notes */
 	uint		nextID;		/* ID of most recently created thread */
 	Proc		*next;		/* linked list of Procs */
 
+
+	void		(*schedfn)(Proc*);	/* function to call in scheduler */
+
 	_Procrend	rend;	/* sleep here for more ready threads */
 
 	void		*arg;			/* passed between shared and unshared stk */
@@ -147,29 +147,17 @@ struct Proc
 
 	void*	udata;		/* User per-proc data pointer */
 	int		nsched;
-};
-
-struct Pqueue {		/* Proc queue */
-	Lock		lock;
-	Proc		*head;
-	Proc		**tail;
-};
 
-struct Ioproc
-{
-	int tid;
-	Channel *c, *creply;
-	int inuse;
-	long (*op)(va_list*);
-	va_list arg;
-	long ret;
-	char err[ERRMAX];
-	Ioproc *next;
+	/*
+	 * for debugging only
+	 */
+	int		pid;			/* process id */
+	int		pthreadid;		/* pthread id */
 };
 
 void		_swaplabel(Label*, Label*);
-void		_freeproc(Proc*);
-Proc*	_newproc(void(*)(void*), void*, uint, char*, int, int);
+Proc*	_newproc(void);
+int		_newthread(Proc*, void(*)(void*), void*, uint, char*, int);
 int		_procsplhi(void);
 void		_procsplx(int);
 int		_sched(void);
@@ -177,7 +165,8 @@ int		_schedexec(Execargs*);
 void		_schedexecwait(void);
 void		_schedexit(Proc*);
 int		_schedfork(Proc*);
-void		_scheduler(void*);
+void		_threadfree(Thread*);
+void		_threadscheduler(void*);
 void		_systhreadinit(void);
 void		_threadassert(char*);
 void		__threaddebug(ulong, char*, ...);
@@ -186,12 +175,15 @@ void		_threadexitsall(char*);
 Proc*	_threadgetproc(void);
 extern void	_threadmultiproc(void);
 Proc*	_threaddelproc(void);
+void		_threadinitproc(Proc*);
+void		_threadwaitkids(Proc*);
 void		_threadsetproc(Proc*);
 void		_threadinitstack(Thread*, void(*)(void*), void*);
+void		_threadlinkmain(void);
 void*	_threadmalloc(long, int);
 void		_threadnote(void*, char*);
 void		_threadready(Thread*);
-void		_threadidle(void);
+void		_threadsetidle(int);
 void		_threadsleep(_Procrend*);
 void		_threadwakeup(_Procrend*);
 void		_threadsignal(void);
@@ -200,13 +192,15 @@ long		_xdec(long*);
 void		_xinc(long*);
 void		_threadremove(Proc*, Thread*);
 void		threadstatus(void);
+void		_threadstartproc(Proc*);
+void		_threadexitproc(char*);
+void		_threadexitallproc(char*);
 
+extern int			_threadnprocs;
 extern int			_threaddebuglevel;
 extern char*		_threadexitsallstatus;
 extern Pqueue		_threadpq;
 extern Channel*	_threadwaitchan;
-extern Rgrp		_threadrgrp;
-extern void _stackfree(void*);
 
 #define DBGAPPL	(1 << 0)
 #define DBGSCHED	(1 << 16)
@@ -216,8 +210,6 @@ extern void _stackfree(void*);
 #define DBGNOTE	(1 << 20)
 #define DBGEXEC	(1 << 21)
 
-#define ioproc_arg(io, type)	(va_arg((io)->arg, type))
-extern int _threadgetpid(void);
 extern void _threadmemset(void*, int, int);
 extern void _threaddebugmemset(void*, int, int);
 extern int _threadprocs;
diff --git a/src/libthread/ucontext.c b/src/libthread/ucontext.c
index 60f803d3..b1c5ef53 100644
--- a/src/libthread/ucontext.c
+++ b/src/libthread/ucontext.c
@@ -6,17 +6,18 @@ _threadinitstack(Thread *t, void (*f)(void*), void *arg)
 	sigset_t zero;
 
 	/* do a reasonable initialization */
-	memset(&t->sched.uc, 0, sizeof t->sched.uc);
+	memset(&t->context.uc, 0, sizeof t->context.uc);
 	sigemptyset(&zero);
-	sigprocmask(SIG_BLOCK, &zero, &t->sched.uc.uc_sigmask);
+	sigprocmask(SIG_BLOCK, &zero, &t->context.uc.uc_sigmask);
 
 	/* call getcontext, because on Linux makecontext neglects floating point */
-	getcontext(&t->sched.uc);
+	getcontext(&t->context.uc);
 
 	/* call makecontext to do the real work. */
-	t->sched.uc.uc_stack.ss_sp = t->stk;
-	t->sched.uc.uc_stack.ss_size = t->stksize;
-	makecontext(&t->sched.uc, (void(*)())f, 1, arg);
+	/* leave a few words open on both ends */
+	t->context.uc.uc_stack.ss_sp = t->stk+8;
+	t->context.uc.uc_stack.ss_size = t->stksize-16;
+	makecontext(&t->context.uc, (void(*)())f, 1, arg);
 }
 
 void
-- 
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