mrun: implement rudimentary event system built on top of mctx

This commit is contained in:
Brian Picciano 2019-01-10 17:58:29 -05:00
parent 92ecb09707
commit 48bb21668a
2 changed files with 146 additions and 0 deletions

View File

@ -94,3 +94,103 @@ func Wait(ctx mctx.Context, cancelCh <-chan struct{}) error {
return nil
}
type ctxEventKeyWrap struct {
key interface{}
}
// Hook describes a function which can be registered to trigger on an event via
// the OnEvent function.
type Hook func(mctx.Context) error
// OnEvent registers a Hook under a typed key. The Hook will be called when
// TriggerEvent is called with that same key. Multiple Hooks can be registered
// for the same key, and will be called sequentially when triggered.
//
// OnEvent registers Hooks onto the root of the given Context. Therefore, Hooks
// will be triggered in the global order they were registered (i.e. if a Hook is
// registered on a Context, then one registered on a child of that Context, then
// another on the original Context again, the three Hooks will be triggered in
// the order: parent, child, parent).
//
// Hooks will be called with whatever Context is passed into TriggerEvent.
func OnEvent(ctx mctx.Context, key interface{}, hook Hook) {
ctx = mctx.Root(ctx)
mctx.GetSetMutableValue(ctx, false, ctxEventKeyWrap{key}, func(v interface{}) interface{} {
hooks, _ := v.([]Hook)
return append(hooks, hook)
})
}
// TriggerEvent causes all Hooks registered with OnEvent under the given key to
// be called sequentially, using the given Context as their input. The given
// Context does not need to be the root Context (see OnEvent).
//
// If any Hook returns an error no further Hooks will be called and that error
// will be returned.
//
// TriggerEvent causes all Hooks which were called to be de-registered. If an
// error caused execution to stop prematurely then any Hooks which were not
// called will remain registered.
func TriggerEvent(ctx mctx.Context, key interface{}) error {
rootCtx := mctx.Root(ctx)
var err error
mctx.GetSetMutableValue(rootCtx, false, ctxEventKeyWrap{key}, func(i interface{}) interface{} {
hooks, _ := i.([]Hook)
for _, hook := range hooks {
hooks = hooks[1:]
// err here is the var outside GetSetMutableValue, we lift it out
if err = hook(ctx); err != nil {
break
}
}
// if there was an error then we want to keep all the hooks which
// weren't called. If there wasn't we want to reset the value to nil so
// the slice doesn't grow unbounded.
if err != nil {
return hooks
}
return nil
})
return err
}
type builtinEvent int
const (
start builtinEvent = iota
stop
)
// OnStart registers the given Hook to run when Start is called. This is a
// special case of OnEvent.
//
// As a convention Hooks running on the start event should block only as long as
// it takes to ensure that whatever is running can do so successfully. For
// short-lived tasks this isn't a problem, but long-lived tasks (e.g. a web
// server) will want to use the Hook only to initialize, and spawn off a
// go-routine to do their actual work. Long-lived tasks should set themselves up
// to stop on the stop event (see OnStop).
func OnStart(ctx mctx.Context, hook Hook) {
OnEvent(ctx, start, hook)
}
// Start runs all Hooks registered using OnStart. This is a special case of
// TriggerEvent.
func Start(ctx mctx.Context) error {
return TriggerEvent(ctx, start)
}
// OnStop registers the given Hook to run when Stop is called. This is a special
// case of OnEvent.
func OnStop(ctx mctx.Context, hook Hook) {
OnEvent(ctx, stop, hook)
}
// Stop runs all Hooks registered using OnStop. This is a special case of
// TriggerEvent.
func Stop(ctx mctx.Context) error {
return TriggerEvent(ctx, stop)
}

View File

@ -6,6 +6,7 @@ import (
"time"
"github.com/mediocregopher/mediocre-go-lib/mctx"
"github.com/mediocregopher/mediocre-go-lib/mtest/massert"
)
func TestThreadWait(t *T) {
@ -140,3 +141,48 @@ func TestThreadWait(t *T) {
})
})
}
func TestEvent(t *T) {
ch := make(chan int, 10)
ctx := mctx.New()
ctxChild := mctx.ChildOf(ctx, "child")
mkHook := func(i int) Hook {
return func(mctx.Context) error {
ch <- i
return nil
}
}
OnEvent(ctx, 0, mkHook(0))
OnEvent(ctxChild, 0, mkHook(1))
OnEvent(ctx, 0, mkHook(2))
bogusErr := errors.New("bogus error")
OnEvent(ctxChild, 0, func(mctx.Context) error { return bogusErr })
OnEvent(ctx, 0, mkHook(3))
OnEvent(ctx, 0, mkHook(4))
massert.Fatal(t, massert.All(
massert.Equal(bogusErr, TriggerEvent(ctx, 0)),
massert.Equal(0, <-ch),
massert.Equal(1, <-ch),
massert.Equal(2, <-ch),
))
// after the error the 3 and 4 Hooks should still be registered, but not
// called yet.
select {
case <-ch:
t.Fatal("Hooks should not have been called yet")
default:
}
massert.Fatal(t, massert.All(
massert.Nil(TriggerEvent(ctx, 0)),
massert.Equal(3, <-ch),
massert.Equal(4, <-ch),
))
}