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238 lines
7.0 KiB
Go
238 lines
7.0 KiB
Go
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// Copyright (c) 2011 - Gustavo Niemeyer <gustavo@niemeyer.net>
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//
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// All rights reserved.
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//
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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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//
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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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//
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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 handles clean goroutine tracking and termination.
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//
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// The zero value of a Tomb is ready to handle the creation of a tracked
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// goroutine via its Go method, and then any tracked goroutine may call
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// the Go method again to create additional tracked goroutines at
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// any point.
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//
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// If any of the tracked goroutines returns a non-nil error, or the
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// Kill or Killf method is called by any goroutine in the system (tracked
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// or not), the tomb Err is set, Alive is set to false, and the Dying
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// channel is closed to flag that all tracked goroutines are supposed
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// to willingly terminate as soon as possible.
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//
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// Once all tracked goroutines terminate, the Dead channel is closed,
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// and Wait unblocks and returns the first non-nil error presented
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// to the tomb via a result or an explicit Kill or Killf method call,
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// or nil if there were no errors.
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//
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// It is okay to create further goroutines via the Go method while
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// the tomb is in a dying state. The final dead state is only reached
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// once all tracked goroutines terminate, at which point calling
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// the Go method again will cause a runtime panic.
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//
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// Tracked functions and methods that are still running while the tomb
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// is in dying state may choose to return ErrDying as their error value.
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// This preserves the well established non-nil error convention, but is
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// understood by the tomb as a clean termination. The Err and Wait
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// methods will still return nil if all observed errors were either
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// nil or ErrDying.
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//
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// For background and a detailed example, see the following blog post:
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//
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// http://blog.labix.org/2011/10/09/death-of-goroutines-under-control
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//
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package tomb
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import (
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"errors"
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"fmt"
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"sync"
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)
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// A Tomb tracks the lifecycle of one or more goroutines as alive,
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// dying or dead, and the reason for their death.
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//
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// See the package documentation for details.
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type Tomb struct {
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m sync.Mutex
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alive int
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dying chan struct{}
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dead chan struct{}
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reason error
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// context.Context is available in Go 1.7+.
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parent interface{}
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child map[interface{}]childContext
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}
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type childContext struct {
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context interface{}
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cancel func()
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done <-chan struct{}
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}
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var (
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ErrStillAlive = errors.New("tomb: still alive")
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ErrDying = errors.New("tomb: dying")
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)
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func (t *Tomb) init() {
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t.m.Lock()
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if t.dead == nil {
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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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}
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t.m.Unlock()
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}
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// Dead returns the channel that can be used to wait until
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// all goroutines have finished running.
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func (t *Tomb) Dead() <-chan struct{} {
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t.init()
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return t.dead
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}
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// Dying returns the channel that can be used to wait until
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// t.Kill is called.
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func (t *Tomb) Dying() <-chan struct{} {
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t.init()
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return t.dying
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}
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// Wait blocks until all goroutines have finished running, and
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// then returns the reason for their death.
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func (t *Tomb) Wait() error {
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t.init()
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<-t.dead
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t.m.Lock()
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reason := t.reason
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t.m.Unlock()
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return reason
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}
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// Go runs f in a new goroutine and tracks its termination.
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//
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// If f returns a non-nil error, t.Kill is called with that
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// error as the death reason parameter.
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//
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// It is f's responsibility to monitor the tomb and return
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// appropriately once it is in a dying state.
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//
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// It is safe for the f function to call the Go method again
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// to create additional tracked goroutines. Once all tracked
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// goroutines return, the Dead channel is closed and the
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// Wait method unblocks and returns the death reason.
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//
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// Calling the Go method after all tracked goroutines return
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// causes a runtime panic. For that reason, calling the Go
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// method a second time out of a tracked goroutine is unsafe.
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func (t *Tomb) Go(f func() error) {
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t.init()
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t.m.Lock()
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defer t.m.Unlock()
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select {
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case <-t.dead:
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panic("tomb.Go called after all goroutines terminated")
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default:
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}
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t.alive++
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go t.run(f)
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}
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func (t *Tomb) run(f func() error) {
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err := f()
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t.m.Lock()
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defer t.m.Unlock()
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t.alive--
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if t.alive == 0 || err != nil {
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t.kill(err)
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if t.alive == 0 {
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close(t.dead)
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}
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}
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}
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// Kill puts the tomb in a dying state for the given reason,
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// closes the Dying channel, and sets Alive to false.
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//
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// Althoguh Kill may be called multiple times, only the first
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// non-nil error is recorded as the death reason.
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//
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// If reason is ErrDying, the previous reason isn't replaced
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// even if nil. It's a runtime error to call Kill with ErrDying
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// if t is not in a dying state.
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func (t *Tomb) Kill(reason error) {
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t.init()
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t.m.Lock()
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defer t.m.Unlock()
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t.kill(reason)
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}
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func (t *Tomb) kill(reason error) {
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if reason == ErrStillAlive {
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panic("tomb: Kill with ErrStillAlive")
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}
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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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}
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return
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}
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if t.reason == ErrStillAlive {
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t.reason = reason
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close(t.dying)
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for _, child := range t.child {
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child.cancel()
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}
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t.child = nil
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return
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}
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if t.reason == nil {
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t.reason = reason
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return
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}
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}
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// Killf calls the Kill method with an error built providing the received
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// parameters 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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t.Kill(err)
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return err
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}
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// Err returns the death reason, or ErrStillAlive if the tomb
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// is not in a dying or dead state.
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func (t *Tomb) Err() (reason error) {
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t.init()
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t.m.Lock()
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reason = t.reason
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t.m.Unlock()
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return
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}
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// Alive returns true if the tomb is not in a dying or dead state.
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func (t *Tomb) Alive() bool {
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return t.Err() == ErrStillAlive
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}
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