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unit.go
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unit.go
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// (c) 2019 Dapper Labs - ALL RIGHTS RESERVED
package engine
import (
"context"
"sync"
"time"
)
// Unit handles synchronization management, startup, and shutdown for engines.
type Unit struct {
admitLock sync.Mutex // used for synchronizing context cancellation with work admittance
wg sync.WaitGroup // tracks in-progress functions
ctx context.Context // context that is cancelled when the unit is Done
cancel context.CancelFunc // cancels the context
sync.Mutex // can be used to synchronize the engine
}
// NewUnit returns a new unit.
func NewUnit() *Unit {
ctx, cancel := context.WithCancel(context.Background())
unit := &Unit{
ctx: ctx,
cancel: cancel,
}
return unit
}
func (u *Unit) admit() bool {
u.admitLock.Lock()
defer u.admitLock.Unlock()
select {
case <-u.ctx.Done():
return false
default:
}
u.wg.Add(1)
return true
}
func (u *Unit) stopAdmitting() {
u.admitLock.Lock()
defer u.admitLock.Unlock()
u.cancel()
}
// Do synchronously executes the input function f unless the unit has shut down.
// It returns the result of f. If f is executed, the unit will not shut down
// until after f returns.
func (u *Unit) Do(f func() error) error {
if !u.admit() {
return nil
}
defer u.wg.Done()
return f()
}
// Launch asynchronously executes the input function unless the unit has shut
// down. If f is executed, the unit will not shut down until after f returns.
func (u *Unit) Launch(f func()) {
if !u.admit() {
return
}
go func() {
defer u.wg.Done()
f()
}()
}
// LaunchAfter asynchronously executes the input function after a certain delay
// unless the unit has shut down.
func (u *Unit) LaunchAfter(delay time.Duration, f func()) {
u.Launch(func() {
select {
case <-u.ctx.Done():
return
case <-time.After(delay):
f()
}
})
}
// LaunchPeriodically asynchronously executes the input function on `interval` periods
// unless the unit has shut down.
// If f is executed, the unit will not shut down until after f returns.
func (u *Unit) LaunchPeriodically(f func(), interval time.Duration, delay time.Duration) {
u.Launch(func() {
ticker := time.NewTicker(interval)
defer ticker.Stop()
select {
case <-u.ctx.Done():
return
case <-time.After(delay):
}
for {
select {
case <-u.ctx.Done():
return
default:
}
select {
case <-u.ctx.Done():
return
case <-ticker.C:
f()
}
}
})
}
// Ready returns a channel that is closed when the unit is ready. A unit is
// ready when the series of "check" functions are executed.
//
// The engine using the unit is responsible for defining these check functions
// as required.
func (u *Unit) Ready(checks ...func()) <-chan struct{} {
ready := make(chan struct{})
go func() {
for _, check := range checks {
check()
}
close(ready)
}()
return ready
}
// Ctx returns a context with the same lifecycle scope as the unit. In particular,
// it is cancelled when Done is called, so it can be used as the parent context
// for processes spawned by any engine whose lifecycle is managed by a unit.
func (u *Unit) Ctx() context.Context {
return u.ctx
}
// Quit returns a channel that is closed when the unit begins to shut down.
func (u *Unit) Quit() <-chan struct{} {
return u.ctx.Done()
}
// Done returns a channel that is closed when the unit is done. A unit is done
// when (i) the series of "action" functions are executed and (ii) all pending
// functions invoked with `Do` or `Launch` have completed.
//
// The engine using the unit is responsible for defining these action functions
// as required.
func (u *Unit) Done(actions ...func()) <-chan struct{} {
done := make(chan struct{})
go func() {
u.stopAdmitting()
for _, action := range actions {
action()
}
u.wg.Wait()
close(done)
}()
return done
}