Allow plugins to have multiple handlers

Currently the plugins pkg allows a single handler. This assumption
breaks down if there are mutiple listeners to a plugin of a certain
Manifest such as NetworkDriver or IpamDriver when swarm-mode is enabled.

Signed-off-by: Madhu Venugopal <madhu@docker.com>
Upstream-commit: 5e9c78aeaf1d88000921190b88a1d91d6261208c
Component: engine

components/engine/pkg/plugins/plugins.go

@@ -43,7 +43,7 @@ type plugins struct {
 
 var (
 	storage          = plugins{plugins: make(map[string]*Plugin)}
-	extpointHandlers = make(map[string]func(string, *Client))
+	extpointHandlers = make(map[string][]func(string, *Client))
 )
 
 // Manifest lists what a plugin implements.
@@ -129,11 +129,13 @@ func (p *Plugin) activateWithLock() error {
 	p.Manifest = m
 
 	for _, iface := range m.Implements {
-		handler, handled := extpointHandlers[iface]
+		handlers, handled := extpointHandlers[iface]
 		if !handled {
 			continue
 		}
-		handler(p.name, p.client)
+		for _, handler := range handlers {
+			handler(p.name, p.client)
+		}
 	}
 	return nil
 }
@@ -226,7 +228,16 @@ func Get(name, imp string) (*Plugin, error) {
 
 // Handle adds the specified function to the extpointHandlers.
 func Handle(iface string, fn func(string, *Client)) {
-	extpointHandlers[iface] = fn
+	handlers, ok := extpointHandlers[iface]
+	if !ok {
+		handlers = []func(string, *Client){}
+	}
+
+	handlers = append(handlers, fn)
+	extpointHandlers[iface] = handlers
+	for _, p := range storage.plugins {
+		p.activated = false
+	}
 }
 
 // GetAll returns all the plugins for the specified implementation