class Continuation - RDoc Documentation (original) (raw)

Continuation objects are generated by Kernel#callcc, after having +require+d continuation. 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:

require "continuation" arr = [ "Freddie", "Herbie", "Ron", "Max", "Ringo" ] callcc{|cc| $cc = cc} puts(message = arr.shift) $cc.call unless message =~ /Max/

produces:

Freddie Herbie Ron Max

Also you can call callcc in other methods:

require "continuation"

def g arr = [ "Freddie", "Herbie", "Ron", "Max", "Ringo" ] cc = callcc { |cc| cc } puts arr.shift return cc, arr.size end

def f c, size = g c.call(c) if size > 1 end

f

This (somewhat contrived) example allows the inner loop to abandon processing early:

require "continuation" callcc {|cont| for i in 0..4 print "#{i}: " for j in i*5...(i+1)*5 cont.call() if j == 17 printf "%3d", j end end } puts

produces:

0: 0 1 2 3 4 1: 5 6 7 8 9 2: 10 11 12 13 14 3: 15 16

Public Instance Methods

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 }
callcc {|cont| cont.call 1 }
callcc {|cont| cont.call 1, 2, 3 }

call(args, ...) click to toggle source

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 }
callcc {|cont| cont.call 1 }
callcc {|cont| cont.call 1, 2, 3 }

static VALUE rb_cont_call(int argc, VALUE *argv, VALUE contval) { rb_context_t *cont = cont_ptr(contval); rb_thread_t *th = GET_THREAD();

if (cont_thread_value(cont) != th->self) {
    rb_raise(rb_eRuntimeError, "continuation called across threads");
}
if (cont->saved_ec.protect_tag != th->ec->protect_tag) {
    rb_raise(rb_eRuntimeError, "continuation called across stack rewinding barrier");
}
if (cont->saved_ec.fiber_ptr) {
    if (th->ec->fiber_ptr != cont->saved_ec.fiber_ptr) {
        rb_raise(rb_eRuntimeError, "continuation called across fiber");
    }
}
rollback_ensure_stack(contval, th->ec->ensure_list, cont->ensure_array);

cont->argc = argc;
cont->value = make_passing_arg(argc, argv);

cont_restore_0(cont, &contval);
UNREACHABLE_RETURN(Qnil);

}

Also aliased as: []