Class: Continuation
Overview
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( = arr.shift)
$cc.call unless =~ /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
Instance Method Summary collapse
-
#[] ⇒ Object
Invokes the continuation.
-
#call ⇒ Object
Invokes the continuation.
Instance Method Details
#call(args, ...) ⇒ Object #[](args, ...) ⇒ Object
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]
|
# File 'cont.c'
/*
* call-seq:
* cont.call(args, ...)
* cont[args, ...]
*
* Invokes the continuation. The program continues from the end of the
* <code>callcc</code> block. If no arguments are given, the original
* <code>callcc</code> returns <code>nil</code>. If one argument is
* given, <code>callcc</code> returns it. Otherwise, an array
* containing <i>args</i> 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_context_t *cont;
rb_thread_t *th = GET_THREAD();
GetContPtr(contval, cont);
if (cont->saved_thread.self != th->self) {
rb_raise(rb_eRuntimeError, "continuation called across threads");
}
if (cont->saved_thread.protect_tag != th->protect_tag) {
rb_raise(rb_eRuntimeError, "continuation called across stack rewinding barrier");
}
if (cont->saved_thread.fiber) {
rb_fiber_t *fcont;
GetFiberPtr(cont->saved_thread.fiber, fcont);
if (th->fiber != cont->saved_thread.fiber) {
rb_raise(rb_eRuntimeError, "continuation called across fiber");
}
}
cont->argc = argc;
cont->value = make_passing_arg(argc, argv);
cont_restore_0(cont, &contval);
return Qnil; /* unreachable */
}
|
#call(args, ...) ⇒ Object #[](args, ...) ⇒ Object
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]
|
# File 'cont.c'
/*
* call-seq:
* cont.call(args, ...)
* cont[args, ...]
*
* Invokes the continuation. The program continues from the end of the
* <code>callcc</code> block. If no arguments are given, the original
* <code>callcc</code> returns <code>nil</code>. If one argument is
* given, <code>callcc</code> returns it. Otherwise, an array
* containing <i>args</i> 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_context_t *cont;
rb_thread_t *th = GET_THREAD();
GetContPtr(contval, cont);
if (cont->saved_thread.self != th->self) {
rb_raise(rb_eRuntimeError, "continuation called across threads");
}
if (cont->saved_thread.protect_tag != th->protect_tag) {
rb_raise(rb_eRuntimeError, "continuation called across stack rewinding barrier");
}
if (cont->saved_thread.fiber) {
rb_fiber_t *fcont;
GetFiberPtr(cont->saved_thread.fiber, fcont);
if (th->fiber != cont->saved_thread.fiber) {
rb_raise(rb_eRuntimeError, "continuation called across fiber");
}
}
cont->argc = argc;
cont->value = make_passing_arg(argc, argv);
cont_restore_0(cont, &contval);
return Qnil; /* unreachable */
}
|