125 lines
4.2 KiB
Go
125 lines
4.2 KiB
Go
package mrun
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import "github.com/mediocregopher/mediocre-go-lib/mctx"
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type ctxEventKeyWrap struct {
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key interface{}
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}
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// Hook describes a function which can be registered to trigger on an event via
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// the RegisterHook function.
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type Hook func(mctx.Context) error
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// RegisterHook registers a Hook under a typed key. The Hook will be called when
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// TriggerHooks is called with that same key. Multiple Hooks can be registered
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// for the same key, and will be called sequentially when triggered.
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//
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// RegisterHook registers Hooks onto the root of the given Context. Therefore,
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// Hooks will be triggered in the global order they were registered. For
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// example: if one Hook is registered on a Context, then one is registered on a
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// child of that Context, then another one is registered on the original Context
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// again, the three Hooks will be triggered in the order: parent, child,
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// parent.
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//
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// Hooks will be called with whatever Context is passed into TriggerHooks.
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func RegisterHook(ctx mctx.Context, key interface{}, hook Hook) {
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ctx = mctx.Root(ctx)
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mctx.GetSetMutableValue(ctx, false, ctxEventKeyWrap{key}, func(v interface{}) interface{} {
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hooks, _ := v.([]Hook)
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return append(hooks, hook)
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})
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}
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func triggerHooks(ctx mctx.Context, key interface{}, next func([]Hook) (Hook, []Hook)) error {
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rootCtx := mctx.Root(ctx)
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var err error
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mctx.GetSetMutableValue(rootCtx, false, ctxEventKeyWrap{key}, func(i interface{}) interface{} {
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var hook Hook
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hooks, _ := i.([]Hook)
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for {
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if len(hooks) == 0 {
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break
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}
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hook, hooks = next(hooks)
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// err here is the var outside GetSetMutableValue, we lift it out
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if err = hook(ctx); err != nil {
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break
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}
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}
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// if there was an error then we want to keep all the hooks which
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// weren't called. If there wasn't we want to reset the value to nil so
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// the slice doesn't grow unbounded.
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if err != nil {
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return hooks
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}
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return nil
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})
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return err
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}
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// TriggerHooks causes all Hooks registered with RegisterHook under the given
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// key to be called in the global order they were registered, using the given
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// Context as their input parameter. The given Context does not need to be the
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// root Context (see RegisterHook).
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//
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// If any Hook returns an error no further Hooks will be called and that error
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// will be returned.
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//
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// TriggerHooks causes all Hooks which were called to be de-registered. If an
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// error caused execution to stop prematurely then any Hooks which were not
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// called will remain registered.
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func TriggerHooks(ctx mctx.Context, key interface{}) error {
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return triggerHooks(ctx, key, func(hooks []Hook) (Hook, []Hook) {
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return hooks[0], hooks[1:]
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})
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}
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// TriggerHooksReverse is the same as TriggerHooks except that registered Hooks
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// are called in the reverse order in which they were registered.
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func TriggerHooksReverse(ctx mctx.Context, key interface{}) error {
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return triggerHooks(ctx, key, func(hooks []Hook) (Hook, []Hook) {
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last := len(hooks) - 1
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return hooks[last], hooks[:last]
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})
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}
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type builtinEvent int
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const (
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start builtinEvent = iota
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stop
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)
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// OnStart registers the given Hook to run when Start is called. This is a
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// special case of RegisterHook.
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//
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// As a convention Hooks running on the start event should block only as long as
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// it takes to ensure that whatever is running can do so successfully. For
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// short-lived tasks this isn't a problem, but long-lived tasks (e.g. a web
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// server) will want to use the Hook only to initialize, and spawn off a
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// go-routine to do their actual work. Long-lived tasks should set themselves up
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// to stop on the stop event (see OnStop).
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func OnStart(ctx mctx.Context, hook Hook) {
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RegisterHook(ctx, start, hook)
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}
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// Start runs all Hooks registered using OnStart. This is a special case of
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// TriggerHooks.
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func Start(ctx mctx.Context) error {
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return TriggerHooks(ctx, start)
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}
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// OnStop registers the given Hook to run when Stop is called. This is a special
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// case of RegisterHook.
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func OnStop(ctx mctx.Context, hook Hook) {
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RegisterHook(ctx, stop, hook)
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}
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// Stop runs all Hooks registered using OnStop in the reverse order in which
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// they were registered. This is a special case of TriggerHooks.
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func Stop(ctx mctx.Context) error {
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return TriggerHooksReverse(ctx, stop)
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}
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