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libthread: deal with _schedfork() and _schedexec() returning -1

The current behaviour of the kernel to deadlock itself
instead of returning an error on fork.

This might change in the future, so prepare libthread
to handle this case.

For _schedfork(), we'r going to just retry forking
on every switch, while for _schedexec(), the exec
will fail and send ~0 down the pid channel.

--- a/sys/src/libthread/create.c

+++ b/sys/src/libthread/create.c

@@ -97,7 +97,8 @@

 	int id;

 	p = _threadgetproc();

-	assert(p->newproc == nil);

+	while(p->newproc)

+		_sched();

 	p->newproc = _newproc(f, arg, stacksize, nil, p->thread->grp, rforkflag);

 	id = p->newproc->threads.head->id;

 	_sched();

--- a/sys/src/libthread/exec.c

+++ b/sys/src/libthread/exec.c

@@ -45,8 +45,10 @@

 	close(p->exec.fd[1]);

 	p->exec.fd[1] = n;

+	while(p->needexec || p->newproc)

+		_sched();

+

 	/* exec in parallel via the scheduler */

-	assert(p->needexec==0);

 	p->exec.prog = prog;

 	p->exec.args = args;

 	p->needexec = 1;

@@ -61,6 +63,8 @@

 	}

 	close(p->exec.fd[0]);

+	if(t->ret == -1)

+		goto Bad;

 	if(pidc)

 		sendul(pidc, t->ret);

--- a/sys/src/libthread/exit.c

+++ b/sys/src/libthread/exit.c

@@ -2,7 +2,6 @@

 #include <libc.h>

 #include <thread.h>

 #include "threadimpl.h"

-#include <tos.h>

 char *_threadexitsallstatus;

 Channel *_threadwaitchan;

@@ -33,7 +32,7 @@

 		exitstr = "";

 	_threadexitsallstatus = exitstr;

 	_threaddebug(DBGSCHED, "_threadexitsallstatus set to %p", _threadexitsallstatus);

-	mypid = _tos->pid; //getpid();

+	mypid = getpid();

 	/*

 	 * signal others.

@@ -47,7 +46,7 @@

 		lock(&_threadpq.lock);

 		npid = 0;

 		for(p = _threadpq.head; p && npid < nelem(pid); p=p->next){

-			if(p->threadint == 0 && p->pid != mypid){

+			if(p->threadint == 0 && p->pid != mypid && p->pid != -1){

 				pid[npid++] = p->pid;

 				p->threadint = 1;

 			}

--- a/sys/src/libthread/id.c

+++ b/sys/src/libthread/id.c

@@ -2,7 +2,6 @@

 #include <libc.h>

 #include <thread.h>

 #include "threadimpl.h"

-#include <tos.h>

 int

 threadid(void)

--- a/sys/src/libthread/main.c

+++ b/sys/src/libthread/main.c

@@ -28,8 +28,6 @@

 	rfork(RFREND);

 	mainp = &p;

-	if(setjmp(_mainjmp))

-		_schedinit(p);

 //_threaddebuglevel = (DBGSCHED|DBGCHAN|DBGREND)^~0;

 	_systhreadinit();

@@ -45,6 +43,7 @@

 	a->argv = argv;

 	p = _newproc(mainlauncher, a, mainstacksize, "threadmain", 0, 0);

+	setjmp(_mainjmp);

 	_schedinit(p);

 	abort();	/* not reached */

 }

@@ -117,18 +116,6 @@

 _schedexit(Proc *p)

 {

 	char ex[ERRMAX];

-	Proc **l;

-

-	lock(&_threadpq.lock);

-	for(l=&_threadpq.head; *l; l=&(*l)->next){

-		if(*l == p){

-			*l = p->next;

-			if(*l == nil)

-				_threadpq.tail = l;

-			break;

-		}

-	}

-	unlock(&_threadpq.lock);

 	utfecpy(ex, ex+sizeof ex, p->exitstr);

 	free(p);

--- a/sys/src/libthread/sched.c

+++ b/sys/src/libthread/sched.c

@@ -2,15 +2,9 @@

 #include <libc.h>

 #include <thread.h>

 #include "threadimpl.h"

-#include <tos.h>

-static Thread	*runthread(Proc*);

-

 static char *_psstate[] = {

-	"Moribund",

 	"Dead",

-	"Exec",

-	"Fork",

 	"Running",

 	"Ready",

 	"Rendezvous",

@@ -24,6 +18,23 @@

 	return _psstate[s];

 }

+static void

+unlinkproc(Proc *p)

+{

+	Proc **l;

+

+	lock(&_threadpq.lock);

+	for(l=&_threadpq.head; *l; l=&(*l)->next){

+		if(*l == p){

+			*l = p->next;

+			if(*l == nil)

+				_threadpq.tail = l;

+			break;

+		}

+	}

+	unlock(&_threadpq.lock);

+}

+

 void

 _schedinit(void *arg)

 {

@@ -31,8 +42,8 @@

 	Thread *t, **l;

 	p = arg;

+	p->pid = getpid();

 	_threadsetproc(p);

-	p->pid = _tos->pid; //getpid();

 	while(setjmp(p->sched))

 		;

 	_threaddebug(DBGSCHED, "top of schedinit, _threadexitsallstatus=%p", _threadexitsallstatus);

@@ -67,8 +78,15 @@

 			p->needexec = 0;

 		}

 		if(p->newproc){

-			t->ret = _schedfork(p->newproc);

-			p->newproc = nil;

+			Thread *x = p->newproc->threads.head;

+			if(x->moribund){

+				x->proc = p;

+				_threadready(x);

+				unlinkproc(p->newproc);

+				free(p->newproc);

+				p->newproc = nil;

+			} else if(_schedfork(p->newproc) != -1)

+				p->newproc = nil;

 		}

 		t->state = t->nextstate;

 		if(t->state == Ready)

@@ -90,12 +108,38 @@

 	if((uchar*)&x - n < (uchar*)t->stk){

 		fprint(2, "%s %lud: &x=%p n=%d t->stk=%p\n",

-			argv0, _tos->pid, &x, n, t->stk);

-		fprint(2, "%s %lud: stack overflow\n", argv0, _tos->pid);

+			argv0, (ulong)p->pid, &x, n, t->stk);

+		fprint(2, "%s %lud: stack overflow\n", argv0, (ulong)p->pid);

 		abort();

 	}

 }

+static Thread*

+runthread(Proc *p)

+{

+	Thread *t;

+	Tqueue *q;

+

+	if(p->nthreads==0)

+		return nil;

+	q = &p->ready;

+	lock(&p->readylock);

+	if(q->head == nil){

+		q->asleep = 1;

+		_threaddebug(DBGSCHED, "sleeping for more work");

+		unlock(&p->readylock);

+		while(rendezvous(q, 0) == (void*)~0){

+			if(_threadexitsallstatus)

+				exits(_threadexitsallstatus);

+		}

+		/* lock picked up from _threadready */

+	}

+	t = q->head;

+	q->head = t->next;

+	unlock(&p->readylock);

+	return t;

+}

+

 void

 _sched(void)

 {

@@ -114,7 +158,8 @@

 		t = runthread(p);

 		if(t == nil){

 			_threaddebug(DBGSCHED, "all threads gone; exiting");

-			_schedexit(p);

+			unlinkproc(p);

+			_schedexit(p);	/* frees proc */

 		}

 		_threaddebug(DBGSCHED, "running %d.%d", t->proc->pid, t->id);

 		p->thread = t;

@@ -126,32 +171,6 @@

 		t->nextstate = Ready;

 		longjmp(t->sched, 1);

 	}

-}

-

-static Thread*

-runthread(Proc *p)

-{

-	Thread *t;

-	Tqueue *q;

-

-	if(p->nthreads==0)

-		return nil;

-	q = &p->ready;

-	lock(&p->readylock);

-	if(q->head == nil){

-		q->asleep = 1;

-		_threaddebug(DBGSCHED, "sleeping for more work");

-		unlock(&p->readylock);

-		while(rendezvous(q, 0) == (void*)~0){

-			if(_threadexitsallstatus)

-				exits(_threadexitsallstatus);

-		}

-		/* lock picked up from _threadready */

-	}

-	t = q->head;

-	q->head = t->next;

-	unlock(&p->readylock);

-	return t;

 }

 void