In Files

  • eval.c

Parent

Methods

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

Public Instance Methods

call(args, ...) click to toggle source
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(argc, argv, cont)
    int argc;
    VALUE *argv;
    VALUE cont;
{
    rb_thread_t th = rb_cont_check(cont);

    if (th->thread != curr_thread->thread) {
        rb_raise(rb_eRuntimeError, "continuation called across threads");
    }
    if (th->thgroup != cont_protect) {
        rb_raise(rb_eRuntimeError, "continuation called across trap");
    }
    switch (argc) {
      case 0:
        th->result = Qnil;
        break;
      case 1:
        th->result = argv[0];
        break;
      default:
        th->result = rb_ary_new4(argc, argv);
        break;
    }

    rb_thread_restore_context(th, RESTORE_NORMAL);
    return Qnil;
}
            
call(args, ...) click to toggle source
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(argc, argv, cont)
    int argc;
    VALUE *argv;
    VALUE cont;
{
    rb_thread_t th = rb_cont_check(cont);

    if (th->thread != curr_thread->thread) {
        rb_raise(rb_eRuntimeError, "continuation called across threads");
    }
    if (th->thgroup != cont_protect) {
        rb_raise(rb_eRuntimeError, "continuation called across trap");
    }
    switch (argc) {
      case 0:
        th->result = Qnil;
        break;
      case 1:
        th->result = argv[0];
        break;
      default:
        th->result = rb_ary_new4(argc, argv);
        break;
    }

    rb_thread_restore_context(th, RESTORE_NORMAL);
    return Qnil;
}