# class Fiber

Fibers are primitives for implementing light weight cooperative concurrency in Ruby. Basically they are a means of creating code blocks that can be paused and resumed, much like threads. The main difference is that they are never preempted and that the scheduling must be done by the programmer and not the VM.

As opposed to other stackless light weight concurrency models, each fiber comes with a stack. This enables the fiber to be paused from deeply nested function calls within the fiber block. See the ruby(1) manpage to configure the size of the fiber stack(s).

When a fiber is created it will not run automatically. Rather it must be explicitly asked to run using the `Fiber#resume` method. The code running inside the fiber can give up control by calling `Fiber.yield` in which case it yields control back to caller (the caller of the `Fiber#resume`).

Upon yielding or termination the `Fiber` returns the value of the last executed expression

For instance:

    fiber = Fiber.new do
      Fiber.yield 1
      2
    end

    puts fiber.resume
    puts fiber.resume
    puts fiber.resume

produces

    1
    2
    FiberError: dead fiber called

The `Fiber#resume` method accepts an arbitrary number of parameters, if it is the first call to `resume` then they will be passed as block arguments. Otherwise they will be the return value of the call to `Fiber.yield`

Example:

    fiber = Fiber.new do |first|
      second = Fiber.yield first + 2
    end

    puts fiber.resume 10
    puts fiber.resume 1_000_000
    puts fiber.resume "The fiber will be dead before I can cause trouble"

produces

    12
    1000000
    FiberError: dead fiber called

### Public Class Methods

current() → fiber click to toggle source

Returns the current fiber. You need to `require 'fiber'` before using this method. If you are not running in the context of a fiber this method will return the root fiber.

    static VALUE
    rb_fiber_s_current(VALUE klass)
    {
        return rb_fiber_current();
    }

yield(args, ...) → obj click to toggle source

Yields control back to the context that resumed the fiber, passing along any arguments that were passed to it. The fiber will resume processing at this point when `resume` is called next. Any arguments passed to the next `resume` will be the value that this `Fiber.yield` expression evaluates to.

    static VALUE
    rb_fiber_s_yield(int argc, VALUE *argv, VALUE klass)
    {
        return rb_fiber_yield_kw(argc, argv, PASS_KW_SPLAT);
    }

### Public Instance Methods

alive? → true or false click to toggle source

Returns true if the fiber can still be resumed (or transferred to). After finishing execution of the fiber block this method will always return false. You need to `require 'fiber'` before using this method.

    VALUE
    rb_fiber_alive_p(VALUE fiber_value)
    {
        return FIBER_TERMINATED_P(fiber_ptr(fiber_value)) ? Qfalse : Qtrue;
    }

inspect()
Alias for: to_s
raise → obj click to toggle source
raise(string) → obj
raise(exception [, string [, array]]) → obj

Raises an exception in the fiber at the point at which the last `Fiber.yield` was called, or at the start if neither `resume` nor `raise` were called before.

With no arguments, raises a `RuntimeError`. With a single `String` argument, raises a `RuntimeError` with the string as a message. Otherwise, the first parameter should be the name of an `Exception` class (or an object that returns an `Exception` object when sent an `exception` message). The optional second parameter sets the message associated with the exception, and the third parameter is an array of callback information. Exceptions are caught by the `rescue` clause of `begin...end` blocks.

    static VALUE
    rb_fiber_raise(int argc, VALUE *argv, VALUE fiber)
    {
        VALUE exc = rb_make_exception(argc, argv);
        return rb_fiber_resume_kw(fiber, -1, &exc, RB_NO_KEYWORDS);
    }

resume(args, ...) → obj click to toggle source

Resumes the fiber from the point at which the last `Fiber.yield` was called, or starts running it if it is the first call to `resume`. Arguments passed to resume will be the value of the `Fiber.yield` expression or will be passed as block parameters to the fiber's block if this is the first `resume`.

Alternatively, when resume is called it evaluates to the arguments passed to the next `Fiber.yield` statement inside the fiber's block or to the block value if it runs to completion without any `Fiber.yield`

    static VALUE
    rb_fiber_m_resume(int argc, VALUE *argv, VALUE fiber)
    {
        return rb_fiber_resume_kw(fiber, argc, argv, PASS_KW_SPLAT);
    }

to_s → string click to toggle source

Returns fiber information string.

    static VALUE
    fiber_to_s(VALUE fiber_value)
    {
        const rb_fiber_t *fiber = fiber_ptr(fiber_value);
        const rb_proc_t *proc;
        char status_info[0x20];

        if (fiber->transferred) {
            snprintf(status_info, 0x20, " (%s, transferred)", fiber_status_name(fiber->status));
        }
        else {
            snprintf(status_info, 0x20, " (%s)", fiber_status_name(fiber->status));
        }

        if (!rb_obj_is_proc(fiber->first_proc)) {
            VALUE str = rb_any_to_s(fiber_value);
            strlcat(status_info, ">", sizeof(status_info));
            rb_str_set_len(str, RSTRING_LEN(str)-1);
            rb_str_cat_cstr(str, status_info);
            return str;
        }
        GetProcPtr(fiber->first_proc, proc);
        return rb_block_to_s(fiber_value, &proc->block, status_info);
    }

Also aliased as: inspect
transfer(args, ...) → obj click to toggle source

Transfer control to another fiber, resuming it from where it last stopped or starting it if it was not resumed before. The calling fiber will be suspended much like in a call to `Fiber.yield`. You need to `require 'fiber'` before using this method.

The fiber which receives the transfer call is treats it much like a resume call. Arguments passed to transfer are treated like those passed to resume.

You cannot call `resume` on a fiber that has been transferred to. If you call `transfer` on a fiber, and later call `resume` on the the fiber, a `FiberError` will be raised. Once you call `transfer` on a fiber, the only way to resume processing the fiber is to call `transfer` on it again.

Example:

    fiber1 = Fiber.new do
      puts "In Fiber 1"
      Fiber.yield
      puts "In Fiber 1 again"
    end

    fiber2 = Fiber.new do
      puts "In Fiber 2"
      fiber1.transfer
      puts "Never see this message"
    end

    fiber3 = Fiber.new do
      puts "In Fiber 3"
    end

    fiber2.resume
    fiber3.resume
    fiber1.resume rescue (p $!)
    fiber1.transfer

produces

    In Fiber 2
    In Fiber 1
    In Fiber 3
    #<FiberError: cannot resume transferred Fiber>
    In Fiber 1 again

    static VALUE
    rb_fiber_m_transfer(int argc, VALUE *argv, VALUE fiber_value)
    {
        rb_fiber_t *fiber = fiber_ptr(fiber_value);
        fiber->transferred = 1;
        return fiber_switch(fiber, argc, argv, 0, PASS_KW_SPLAT);
    }