From 87a96ece672be026bb8e720f62777f6bb94e47af Mon Sep 17 00:00:00 2001
From: jsteemann <jan@arangodb.com>
Date: Fri, 15 Jul 2016 12:40:29 +0200
Subject: [PATCH] engine selection

---
 arangod/StorageEngine/EngineSelectorFeature.cpp | 14 +++++++++++++-
 arangod/StorageEngine/EngineSelectorFeature.h   |  9 +++++++++
 arangod/StorageEngine/MMFilesEngine.cpp         |  4 ++++
 arangod/StorageEngine/OtherEngine.cpp           |  4 ++++
 4 files changed, 30 insertions(+), 1 deletion(-)

diff --git a/arangod/StorageEngine/EngineSelectorFeature.cpp b/arangod/StorageEngine/EngineSelectorFeature.cpp
index 15a97b7680..d706c187ea 100644
--- a/arangod/StorageEngine/EngineSelectorFeature.cpp
+++ b/arangod/StorageEngine/EngineSelectorFeature.cpp
@@ -31,6 +31,8 @@
 using namespace arangodb;
 using namespace arangodb::options;
 
+StorageEngine* EngineSelectorFeature::ENGINE = nullptr;
+
 EngineSelectorFeature::EngineSelectorFeature(
     application_features::ApplicationServer* server)
     : ApplicationFeature(server, "EngineSelector"), _engine(MMFilesEngine::EngineName) {
@@ -54,15 +56,25 @@ void EngineSelectorFeature::prepare() {
       // this is the selected engine
       LOG(TRACE) << "enabling storage engine " << engine;
       e->enable();
+
+      // register storage engine
+      ENGINE = e;
     } else {
       // turn off all other storage engines
       LOG(TRACE) << "disabling storage engine " << engine;
       e->disable();
     }
   }
+
+  TRI_ASSERT(ENGINE != nullptr);
 }
 
-// all available storage engines
+void EngineSelectorFeature::unprepare() {
+  // unregister storage engine
+  ENGINE = nullptr;
+}
+
+// return all available storage engines
 std::unordered_set<std::string> EngineSelectorFeature::availableEngines() { 
   return std::unordered_set<std::string>{
     MMFilesEngine::EngineName, 
diff --git a/arangod/StorageEngine/EngineSelectorFeature.h b/arangod/StorageEngine/EngineSelectorFeature.h
index 8e3c690c47..70fd5eacf8 100644
--- a/arangod/StorageEngine/EngineSelectorFeature.h
+++ b/arangod/StorageEngine/EngineSelectorFeature.h
@@ -27,6 +27,8 @@
 #include "ProgramOptions/ProgramOptions.h"
 
 namespace arangodb {
+class StorageEngine;
+
 class EngineSelectorFeature final : public application_features::ApplicationFeature {
  public:
   explicit EngineSelectorFeature(application_features::ApplicationServer* server);
@@ -34,8 +36,15 @@ class EngineSelectorFeature final : public application_features::ApplicationFeat
  public:
   void collectOptions(std::shared_ptr<options::ProgramOptions>) override final;
   void prepare() override final;
+  void unprepare() override final;
   
+  // return the names of all available storage engines
   static std::unordered_set<std::string> availableEngines();
+  
+ public:
+  // selected storage engine. this will contain a pointer to the storage engine after
+  // prepare() and before unprepare()
+  static StorageEngine* ENGINE;
 
  private:
   std::string _engine;
diff --git a/arangod/StorageEngine/MMFilesEngine.cpp b/arangod/StorageEngine/MMFilesEngine.cpp
index 9f139323bd..8c620886a8 100644
--- a/arangod/StorageEngine/MMFilesEngine.cpp
+++ b/arangod/StorageEngine/MMFilesEngine.cpp
@@ -22,6 +22,7 @@
 ////////////////////////////////////////////////////////////////////////////////
 
 #include "MMFilesEngine.h"
+#include "StorageEngine/EngineSelectorFeature.h"
 
 using namespace arangodb;
 
@@ -46,17 +47,20 @@ void MMFilesEngine::validateOptions(std::shared_ptr<options::ProgramOptions>) {
 // preparation phase for storage engine. can be used for internal setup.
 // the storage engine must not start any threads here or write any files
 void MMFilesEngine::prepare() {
+  TRI_ASSERT(EngineSelectorFeature::ENGINE = this);
 }
   
 // start the engine. now it's allowed to start engine-specific threads,
 // write files etc.
 void MMFilesEngine::start() {
+  TRI_ASSERT(EngineSelectorFeature::ENGINE = this);
 }
 
 // stop the storage engine. this can be used to flush all data to disk,
 // shutdown threads etc. it is guaranteed that there will be no read and
 // write requests to the storage engine after this call
 void MMFilesEngine::stop() {
+  TRI_ASSERT(EngineSelectorFeature::ENGINE = this);
 }
 
 // fill the Builder object with an array of databases that were detected
diff --git a/arangod/StorageEngine/OtherEngine.cpp b/arangod/StorageEngine/OtherEngine.cpp
index 5dee8a2100..5e4fdd1c5c 100644
--- a/arangod/StorageEngine/OtherEngine.cpp
+++ b/arangod/StorageEngine/OtherEngine.cpp
@@ -22,6 +22,7 @@
 ////////////////////////////////////////////////////////////////////////////////
 
 #include "OtherEngine.h"
+#include "StorageEngine/EngineSelectorFeature.h"
 
 using namespace arangodb;
 
@@ -46,17 +47,20 @@ void OtherEngine::validateOptions(std::shared_ptr<options::ProgramOptions>) {
 // preparation phase for storage engine. can be used for internal setup.
 // the storage engine must not start any threads here or write any files
 void OtherEngine::prepare() {
+  TRI_ASSERT(EngineSelectorFeature::ENGINE = this);
 }
   
 // start the engine. now it's allowed to start engine-specific threads,
 // write files etc.
 void OtherEngine::start() {
+  TRI_ASSERT(EngineSelectorFeature::ENGINE = this);
 }
 
 // stop the storage engine. this can be used to flush all data to disk,
 // shutdown threads etc. it is guaranteed that there will be no read and
 // write requests to the storage engine after this call
 void OtherEngine::stop() {
+  TRI_ASSERT(EngineSelectorFeature::ENGINE = this);
 }
 
 // fill the Builder object with an array of databases that were detected