Class: Fiber

Inherits:
Object show all
Defined in:
cont.c,
cont.c

Overview

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 small 4KB stack. This enables the fiber to be paused from deeply nested function calls within the fiber block.

When a fiber is created it will not run automatically. Rather it must be 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 14
puts fiber.resume 18

produces

12
14
FiberError: dead fiber called

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initializeObject

:nodoc:


1214
1215
1216
1217
1218
# File 'cont.c', line 1214

static VALUE
rb_fiber_init(VALUE fibval)
{
    return fiber_init(fibval, rb_block_proc());
}

Class Method Details

.currentObject

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.


1628
1629
1630
1631
1632
# File 'cont.c', line 1628

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

.yield(args, ...) ⇒ Object

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.

Returns:


1614
1615
1616
1617
1618
# File 'cont.c', line 1614

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

Instance Method Details

#alive?Boolean

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.

Returns:

  • (Boolean)

Returns:

  • (Boolean)

1521
1522
1523
1524
1525
1526
1527
# File 'cont.c', line 1521

VALUE
rb_fiber_alive_p(VALUE fibval)
{
    rb_fiber_t *fib;
    GetFiberPtr(fibval, fib);
    return fib->status != TERMINATED ? Qtrue : Qfalse;
}

#resume(args, ...) ⇒ Object

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

Returns:


1544
1545
1546
1547
1548
# File 'cont.c', line 1544

static VALUE
rb_fiber_m_resume(int argc, VALUE *argv, VALUE fib)
{
    return rb_fiber_resume(fib, argc, argv);
}

#transfer(args, ...) ⇒ Object

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 resume a fiber that transferred control to another one. This will cause a double resume error. You need to transfer control back to this fiber before it can yield and resume.

Example:

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

<em>produces</em>

In fiber 2
In fiber 1
In fiber 3

Returns:


1595
1596
1597
1598
1599
1600
1601
1602
# File 'cont.c', line 1595

static VALUE
rb_fiber_m_transfer(int argc, VALUE *argv, VALUE fibval)
{
    rb_fiber_t *fib;
    GetFiberPtr(fibval, fib);
    fib->transfered = 1;
    return rb_fiber_transfer(fibval, argc, argv);
}