/**********************************************************************
cont.c -
$Author$
$Date$
created at: Thu May 23 09:03:43 2007
Copyright (C) 2007 Koichi Sasada
**********************************************************************/
#include "ruby.h"
#include "yarvcore.h"
#include "gc.h"
#include "eval_intern.h"
typedef struct rb_continuation_struct {
rb_thread_t saved_thread;
rb_jmpbuf_t jmpbuf;
VALUE retval;
VALUE *vm_stack;
VALUE *machine_stack;
VALUE *machine_stack_src;
int machine_stack_size;
} rb_continuation_t;
#define GetContPtr(obj, ptr) \
Data_Get_Struct(obj, rb_continuation_t, ptr)
NOINLINE(static VALUE cont_capture(volatile int *stat));
void rb_thread_mark(rb_thread_t *th);
static void
cont_mark(void *ptr)
{
MARK_REPORT_ENTER("cont");
if (ptr) {
rb_continuation_t *cont = ptr;
rb_gc_mark(cont->retval);
rb_thread_mark(&cont->saved_thread);
if (cont->vm_stack) {
rb_gc_mark_locations(cont->vm_stack,
cont->vm_stack + cont->saved_thread.stack_size);
}
if (cont->machine_stack) {
rb_gc_mark_locations(cont->machine_stack,
cont->machine_stack + cont->machine_stack_size);
}
}
MARK_REPORT_LEAVE("cont");
}
static void
cont_free(void *ptr)
{
FREE_REPORT_ENTER("cont");
if (ptr) {
rb_continuation_t *cont = ptr;
FREE_UNLESS_NULL(cont->machine_stack);
FREE_UNLESS_NULL(cont->vm_stack);
ruby_xfree(ptr);
}
FREE_REPORT_LEAVE("cont");
}
static VALUE
cont_capture(volatile int *stat)
{
rb_continuation_t *cont;
VALUE contval;
rb_thread_t *th = GET_THREAD(), *sth;
int size;
contval = Data_Make_Struct(rb_cCont, rb_continuation_t,
cont_mark, cont_free, cont);
/* save context */
cont->saved_thread = *th;
sth = &cont->saved_thread;
sth->stack = 0; /* clear to skip GC marking */
cont->vm_stack = ALLOC_N(VALUE, sth->stack_size);
MEMCPY(cont->vm_stack, th->stack, VALUE, sth->stack_size);
rb_gc_set_stack_end(&th->machine_stack_end);
if (th->machine_stack_start > th->machine_stack_end) {
size = cont->machine_stack_size = th->machine_stack_start - th->machine_stack_end;
cont->machine_stack_src = th->machine_stack_end;
}
else {
size = cont->machine_stack_size = th->machine_stack_end - th->machine_stack_start;
cont->machine_stack_src = th->machine_stack_start;
}
cont->machine_stack = ALLOC_N(VALUE, size);
MEMCPY(cont->machine_stack, cont->machine_stack_src, VALUE, size);
if (ruby_setjmp(cont->jmpbuf)) {
VALUE retval;
retval = cont->retval;
cont->retval = Qnil;
*stat = 1;
return retval;
}
else {
*stat = 0;
return contval;
}
}
static void
cont_restore_context_1(rb_continuation_t *cont)
{
rb_thread_t *th = GET_THREAD(), *sth = &cont->saved_thread;
/* restore thread context */
MEMCPY(th->stack, cont->vm_stack, VALUE, sth->stack_size);
th->cfp = sth->cfp;
th->safe_level = sth->safe_level;
th->raised_flag = sth->raised_flag;
th->state = sth->state;
th->status = sth->status;
th->tag = sth->tag;
/* restore machine stack */
MEMCPY(cont->machine_stack_src, cont->machine_stack,
VALUE, cont->machine_stack_size);
ruby_longjmp(cont->jmpbuf, 1);
}
NORETURN(NOINLINE(static void restore_context_0(rb_continuation_t *, VALUE *)));
static void
cont_restore_context_0(rb_continuation_t *cont, VALUE *addr_in_prev_frame)
{
#define STACK_PAD_SIZE 1024
VALUE space[STACK_PAD_SIZE];
#if STACK_GROW_DIRECTION < 0 /* downward */
if (addr_in_prev_frame > cont->machine_stack_src) {
cont_restore_context_0(cont, &space[0]);
}
#elif STACK_GROW_DIRECTION > 0 /* upward */
if (addr_in_prev_frame < cont->machine_stack_src + cont->machine_stack_size) {
cont_restore_context_0(cont, &space[STACK_PAD_SIZE-1]);
}
#else
if (addr_in_prev_frame > &space[0]) {
/* Stack grows downward */
if (addr_in_prev_frame > cont->saved_thread.machine_stack_src) {
cont_restore_context_0(cont, &space[0]);
}
}
else {
/* Stack grows upward */
if (addr_in_prev_frame < cont->machine_stack_src + cont->machine_stack_size) {
cont_restore_context_0(cont, &space[STACK_PAD_SIZE-1]);
}
}
#endif
cont_restore_context_1(cont);
}
/*
* Document-class: Continuation
*
* Continuation objects are generated by
* Kernel#callcc
. They hold a return address and execution
* context, allowing a nonlocal return to the end of the
* callcc
block from anywhere within a program.
* Continuations are somewhat analogous to a structured version of C's
* setjmp/longjmp
(although they contain more state, so
* you might consider them closer to threads).
*
* For instance:
*
* arr = [ "Freddie", "Herbie", "Ron", "Max", "Ringo" ]
* callcc{|$cc|}
* puts(message = arr.shift)
* $cc.call unless message =~ /Max/
*
* produces:
*
* Freddie
* Herbie
* Ron
* Max
*
* This (somewhat contrived) example allows the inner loop to abandon
* processing early:
*
* callcc {|cont|
* for i in 0..4
* print "\n#{i}: "
* for j in i*5...(i+1)*5
* cont.call() if j == 17
* printf "%3d", j
* end
* end
* }
* print "\n"
*
* produces:
*
* 0: 0 1 2 3 4
* 1: 5 6 7 8 9
* 2: 10 11 12 13 14
* 3: 15 16
*/
VALUE rb_cCont;
/*
* call-seq:
* callcc {|cont| block } => obj
*
* Generates a Continuation
object, which it passes to the
* associated block. Performing a cont.call
will
* cause the callcc
to return (as will falling through the
* end of the block). The value returned by the callcc
is
* the value of the block, or the value passed to
* cont.call
. See class Continuation
* for more details. Also see Kernel::throw
for
* an alternative mechanism for unwinding a call stack.
*/
static VALUE
rb_callcc(VALUE self)
{
volatile int called;
volatile VALUE val = cont_capture(&called);
if (called) {
return val;
}
else {
return rb_yield(val);
}
}
/*
* call-seq:
* cont.call(args, ...)
* cont[args, ...]
*
* Invokes the continuation. The program continues from the end of the
* callcc
block. If no arguments are given, the original
* callcc
returns nil
. If one argument is
* given, callcc
returns it. Otherwise, an array
* containing args is returned.
*
* callcc {|cont| cont.call } #=> nil
* callcc {|cont| cont.call 1 } #=> 1
* callcc {|cont| cont.call 1, 2, 3 } #=> [1, 2, 3]
*/
static VALUE
rb_cont_call(int argc, VALUE *argv, VALUE contval)
{
rb_continuation_t *cont;
rb_thread_t *th = GET_THREAD();
GetContPtr(contval, cont);
if (cont->saved_thread.value != th->value) {
rb_raise(rb_eRuntimeError, "continuation called across threads");
}
if (cont->saved_thread.trap_tag != th->trap_tag) {
rb_raise(rb_eRuntimeError, "continuation called across trap");
}
switch(argc) {
case 0:
cont->retval = Qnil;
break;
case 1:
cont->retval = argv[0];
break;
default:
cont->retval = rb_ary_new4(argc, argv);
break;
}
cont_restore_context_0(cont, (VALUE *)&cont);
return Qnil; /* unreachable */
}
void
Init_Cont(void)
{
rb_cCont = rb_define_class("Continuation", rb_cObject);
rb_undef_alloc_func(rb_cCont);
rb_undef_method(CLASS_OF(rb_cCont), "new");
rb_define_method(rb_cCont, "call", rb_cont_call, -1);
rb_define_method(rb_cCont, "[]", rb_cont_call, -1);
rb_define_global_function("callcc", rb_callcc, 0);
}