[9fans] portable 9-style threads libraries

[9fans] portable 9-style threads libraries

[rog]

i've just been queried by a friend (and i'd like to know anyway):

a) has anyone bundled up the plan9 libthread into a package portable
to other systems?

b) i seem to remember another very lightweight portable thread library
produced by someone plan 9 related, but can't seem to find any
references.  any ideas?

Re: [9fans] portable 9-style threads libraries

[Russ Cox]

> a) has anyone bundled up the plan9 libthread into a package portable
> to other systems?

just yesterday, in fact, i packaged up libthread
and the current versions of the other libraries.
i haven't put them out for playing yet.  i'm a little
worried that my unix implementation of the rendezvous
system call is too heavyweight for switch-intensive jobs.

> b) i seem to remember another very lightweight portable thread library
> produced by someone plan 9 related, but can't seem to find any
> references.  any ideas?

if all you want is user-level threads (only one proc)
then i have an even lighter-weight library that works
better for programs you're willing to tailor to unix.
you can designate an idle function.  on unix it works
well to make this a wrapper around select.  sadly.

the original tra sources (and perhaps the ones still in
the anonymous cvs) used a stack-copying thread implementation
that was fairly portable.  the stack copying got around
stack overflow -- you were always on the system stack --
though it introduced the plan 9 "all stack variables are
thread local" complication/feature.  the initial plan 9 stab
at this version is below.

russ


/*
 * Stack-copying context switching.
 * Assumes stack grows toward lower addresses.
 */
#include <u.h>
#include <libc.h>

jmp_buf mainjmp;

typedef struct Label Label;
struct Label
{
	void *stk;
	jmp_buf jb;
};

void*
emalloc(int n)
{
	void *a;

	a = mallocz(n, 1);
	if(a==nil)
		sysfatal("out of memory");
	return a;
}

static void swtch0(Label*, Label*);
static void swtch1(Label*);
static void swtch2(Label*);

/* the abort() calls keep smart compilers from optimizing the tail recursion */

void
switchlabel(Label *cur, Label *nxt)
{
	/*
	 * save the current stack position and registers
	 * the first time through.  swtch0 won't return.
	 */
	if(setjmp(cur->jb)==0){
		swtch0(cur, nxt);
		abort();
	}
}

static void
swtch0(Label *cur, Label *nxt)
{
	uchar *lo, *hi;
	int n;

	/* save the stack for the current thread */
	lo = (uchar*)cur->jb[JMPBUFSP];
	hi = (uchar*)mainjmp[JMPBUFSP];
	n = hi-lo;
	cur->stk = emalloc(n);
	memmove(cur->stk, lo, n);

	/* switch to the next thread */
	swtch1(nxt);
	abort();
}

static void
swtch1(Label *nxt)
{
	uchar buf[64];	/* take up stack space */

	/* recurse until we're out of the area the new stack will occupy. */
	if(nxt->jb[JMPBUFSP] < (ulong)buf)
		swtch1(nxt);

	/* do the copy */
	swtch2(nxt);
	abort();
}

static void
swtch2(Label *nxt)
{
	uchar *lo, *hi;
	int n;

	/* put the next stack in place */
	lo = (uchar*)nxt->jb[JMPBUFSP];
	hi = (uchar*)mainjmp[JMPBUFSP];
	n = hi-lo;
	memmove(lo, nxt->stk, n);

	free(nxt->stk);
	nxt->stk = nil;

	/* hop to it */
	longjmp(nxt->jb, 1);
	abort();
}

void
initlabel(Label *l, void (*fn)(void*), void *arg)
{
	ulong *stk;
	int n;

	n = 16;
	l->stk = emalloc(n);
	stk = (ulong*)((uchar*)l->stk + n);
	--stk;
	*--stk = (ulong)arg;
	*--stk = 0;	/* return address */
	*--stk = 0;	/* new pc */
	l->jb[JMPBUFPC] = (ulong)fn+JMPBUFDPC;
	l->jb[JMPBUFSP] = mainjmp[JMPBUFSP]-n;
}

Label ml, pl;

void
printthread(void *a)
{
	print("printthread runs, arg is %d\n", (int)a);
	switchlabel(&pl, &ml);
}

void
main(int argc, char **argv)
{
	setjmp(mainjmp);

	initlabel(&pl, printthread, (void*)12345);
	print("main runs\n");
	switchlabel(&ml, &pl);
	print("main runs again\n");
	exits(nil);
}

Re: [9fans] portable 9-style threads libraries

[Russ Cox]

http://pdos.lcs.mit.edu/~rsc/software/
has current libutf, libfmt, libbio, libregexp,
lib9 (libc bits that don't fit anywhere else),
libthread, mk, and sam4e (thanks to scott schwartz).

Re: [9fans] portable 9-style threads libraries

[Russ Cox]

> I couldn't download about half of the files -- the server gives me 404.

Whoops.  The ones that did download were old.
I had named today's files .tar.gz but the links .tgz.
It should be fixed now.

Thanks.

Re: [9fans] portable 9-style threads libraries

[goga]

On Fri, Sep 26, 2003 at 03:21:23PM -0400, Russ Cox wrote:
> http://pdos.lcs.mit.edu/~rsc/software/
> has current libutf, libfmt, libbio, libregexp,
> lib9 (libc bits that don't fit anywhere else),
> libthread, mk, and sam4e (thanks to scott schwartz).
>
I couldn't download about half of the files -- the server gives me 404.

	goga

Re: [9fans] portable 9-style threads libraries

[goga]

On Fri, Sep 26, 2003 at 05:36:58PM -0400, Russ Cox wrote:
> > I couldn't download about half of the files -- the server gives me 404.
>
> Whoops.  The ones that did download were old.
> I had named today's files .tar.gz but the links .tgz.
> It should be fixed now.
>
> Thanks.
>
Now it works. Thank you!

	goga