adaptation: implement plugin synchronization blocks.

Add a mechanism to block and unblock plugin synchronization.
We use this first in our tests to ensure that test plugins
get properly synchronized either before or after we create
a pod or a container, but not halfway through it.

We should also do the same in the corresponding paths of the
NRI runtime integration core where otherwise processing NRI
events concurrent to plugin registration could result in an
inconsistent initial state of a new plugin (missing pods or
containers during sync, or omitted event for the plugin).

Signed-off-by: Krisztian Litkey <krisztian.litkey@intel.com>

Author: klihub

pkg/adaptation/adaptation.go

@@ -65,6 +65,7 @@ type Adaptation struct {
 	serverOpts []ttrpc.ServerOpt
 	listener   net.Listener
 	plugins    []*plugin
+	syncLock   sync.RWMutex
 }
 
 var (
@@ -135,6 +136,7 @@ func New(name, version string, syncFn SyncFn, updateFn UpdateFn, opts ...Option)
 		pluginPath: DefaultPluginPath,
 		dropinPath: DefaultPluginConfigPath,
 		socketPath: DefaultSocketPath,
+		syncLock:   sync.RWMutex{},
 	}
 
 	for _, o := range opts {
@@ -464,6 +466,8 @@ func (r *Adaptation) acceptPluginConnections(l net.Listener) error {
 				continue
 			}
 
+			r.requestPluginSync()
+
 			err = r.syncFn(ctx, p.synchronize)
 			if err != nil {
 				log.Infof(ctx, "failed to synchronize plugin: %v", err)
@@ -472,9 +476,10 @@ func (r *Adaptation) acceptPluginConnections(l net.Listener) error {
 				r.plugins = append(r.plugins, p)
 				r.sortPlugins()
 				r.Unlock()
-
 				log.Infof(ctx, "plugin %q connected and synchronized", p.name())
 			}
+
+			r.finishedPluginSync()
 		}
 	}()
 
@@ -545,3 +550,30 @@ func (r *Adaptation) sortPlugins() {
 		}
 	}
 }
+
+func (r *Adaptation) requestPluginSync() {
+	r.syncLock.Lock()
+}
+
+func (r *Adaptation) finishedPluginSync() {
+	r.syncLock.Unlock()
+}
+
+type PluginSyncBlock struct {
+	r *Adaptation
+}
+
+// BlockPluginSync blocks plugins from being synchronized/fully registered.
+func (r *Adaptation) BlockPluginSync() *PluginSyncBlock {
+	r.syncLock.RLock()
+	return &PluginSyncBlock{r: r}
+}
+
+// Unblock a plugin sync. block put in place by BlockPluginSync. Safe to call
+// multiple times but only from a single goroutine.
+func (b *PluginSyncBlock) Unblock() {
+	if b != nil && b.r != nil {
+		b.r.syncLock.RUnlock()
+		b.r = nil
+	}
+}