Added remove-executor hook for slave.

Review: https://reviews.apache.org/r/28875

src/hook/hook.hpp

@@ -58,6 +58,16 @@ class Hook
   {
     return None();
   }
+
+  // This hook is called from within slave when an executor is being
+  // removed.  A typical module implementing the hook will perform
+  // some cleanup as required.
+  virtual Try<Nothing> slaveRemoveExecutorHook(
+      const FrameworkInfo& frameworkInfo,
+      const ExecutorInfo& executorInfo)
+  {
+    return Nothing();
+  }
 };
 
 } // namespace internal {

src/hook/manager.cpp

@@ -132,5 +132,20 @@ Environment HookManager::slaveLaunchExecutorEnvironmentDecorator(
   return environment;
 }
 
+
+void HookManager::slaveRemoveExecutorHook(
+    const FrameworkInfo& frameworkInfo,
+    const ExecutorInfo& executorInfo)
+{
+  foreachpair (const string& name, Hook* hook, availableHooks) {
+    const Try<Nothing>& result =
+      hook->slaveRemoveExecutorHook(frameworkInfo, executorInfo);
+    if (result.isError()) {
+      LOG(WARNING) << "Slave remove executor hook failed for module '"
+                   << name << "': " << result.error();
+    }
+  }
+}
+
 } // namespace internal {
 } // namespace mesos {

src/hook/manager.hpp

@@ -48,6 +48,10 @@ class HookManager
   static Environment slaveLaunchExecutorEnvironmentDecorator(
       const ExecutorInfo& executorInfo,
       const TaskInfo& taskInfo);
+
+  static void slaveRemoveExecutorHook(
+      const FrameworkInfo& frameworkInfo,
+      const ExecutorInfo& executorInfo);
 };
 
 } // namespace internal {

src/slave/slave.cpp

@@ -3123,6 +3123,8 @@ void Slave::removeExecutor(Framework* framework, Executor* executor)
     }
   }
 
+  HookManager::slaveRemoveExecutorHook(framework->info, executor->info);
+
   framework->destroyExecutor(executor->id);
 }