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// Copyright (c) 2011 - Gustavo Niemeyer <gustavo@niemeyer.net>
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// All rights reserved.
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are met:
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// * Redistributions of source code must retain the above copyright notice,
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// this list of conditions and the following disclaimer.
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// * Redistributions in binary form must reproduce the above copyright notice,
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// this list of conditions and the following disclaimer in the documentation
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// and/or other materials provided with the distribution.
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// * Neither the name of the copyright holder nor the names of its
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// contributors may be used to endorse or promote products derived from
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// this software without specific prior written permission.
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
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// CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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// EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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// PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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// LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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// NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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// The tomb package helps with clean goroutine termination.
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// See the Tomb type for details.
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// A Tomb tracks the lifecycle of a goroutine as alive, dying or dead,
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// and the reason for its death.
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// The zero value of a Tomb assumes that a goroutine is about to be
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// created or already alive. Once Kill or Killf is called with an
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// argument that informs the reason for death, the goroutine is in
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// a dying state and is expected to terminate soon. Right before the
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// goroutine function or method returns, Done must be called to inform
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// that the goroutine is indeed dead and about to stop running.
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// A Tomb exposes Dying and Dead channels. These channels are closed
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// when the Tomb state changes in the respective way. They enable
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// explicit blocking until the state changes, and also to selectively
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// unblock select statements accordingly.
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// When the tomb state changes to dying and there's still logic going
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// on within the goroutine, nested functions and methods may choose to
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// return ErrDying as their error value, as this error won't alter the
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// tomb state if provied to the Kill method. This is a convenient way to
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// follow standard Go practices in the context of a dying tomb.
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// For background and a detailed example, see the following blog post:
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// http://blog.labix.org/2011/10/09/death-of-goroutines-under-control
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// For a more complex code snippet demonstrating the use of multiple
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// goroutines with a single Tomb, see:
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// http://play.golang.org/p/Xh7qWsDPZP
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ErrStillAlive = errors.New("tomb: still alive")
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ErrDying = errors.New("tomb: dying")
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func (t *Tomb) init() {
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t.dead = make(chan struct{})
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t.dying = make(chan struct{})
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t.reason = ErrStillAlive
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// Dead returns the channel that can be used to wait
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// until t.Done has been called.
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func (t *Tomb) Dead() <-chan struct{} {
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// Dying returns the channel that can be used to wait
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// until t.Kill or t.Done has been called.
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func (t *Tomb) Dying() <-chan struct{} {
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// Wait blocks until the goroutine is in a dead state and returns the
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// reason for its death.
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func (t *Tomb) Wait() error {
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// Done flags the goroutine as dead, and should be called a single time
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// right before the goroutine function or method returns.
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// If the goroutine was not already in a dying state before Done is
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// called, it will be flagged as dying and dead at once with no
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func (t *Tomb) Done() {
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// Kill flags the goroutine as dying for the given reason.
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// Kill may be called multiple times, but only the first
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// non-nil error is recorded as the reason for termination.
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// If reason is ErrDying, the previous reason isn't replaced
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// even if it is nil. It's a runtime error to call Kill with
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// ErrDying if t is not in a dying state.
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func (t *Tomb) Kill(reason error) {
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if reason == ErrDying {
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if t.reason == ErrStillAlive {
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panic("tomb: Kill with ErrDying while still alive")
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if t.reason == nil || t.reason == ErrStillAlive {
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// If the receive on t.dying succeeds, then
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// it can only be because we have already closed it.
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// If it blocks, then we know that it needs to be closed.
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// Killf works like Kill, but builds the reason providing the received
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// arguments to fmt.Errorf. The generated error is also returned.
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func (t *Tomb) Killf(f string, a ...interface{}) error {
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err := fmt.Errorf(f, a...)
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// Err returns the reason for the goroutine death provided via Kill
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// or Killf, or ErrStillAlive when the goroutine is still alive.
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func (t *Tomb) Err() (reason error) {