scheduler: tag executors with app id

Thus far, we tagged executors with the (user, function) pair. This is
needed in multi-threaded environments, where different threads must
share the same executor. However, using only the (user, function) pair
prevents the execution concurrent applications with the same pair.

Instead, the correct thing to do is to track applications using the
(user, function) pair in conjunction with the application id.

src/scheduler/Scheduler.cpp

@@ -243,7 +243,7 @@ int Scheduler::reapStaleExecutors()
 long Scheduler::getFunctionExecutorCount(const faabric::Message& msg)
 {
     faabric::util::SharedLock lock(mx);
-    const std::string funcStr = faabric::util::funcToString(msg, false);
+    const std::string funcStr = faabric::util::funcToString(msg, true);
     return executors[funcStr].size();
 }
 
@@ -252,7 +252,8 @@ void Scheduler::executeBatch(std::shared_ptr<faabric::BatchExecuteRequest> req)
     faabric::util::FullLock lock(mx);
 
     bool isThreads = req->type() == faabric::BatchExecuteRequest::THREADS;
-    auto funcStr = faabric::util::funcToString(req);
+    auto funcStr = faabric::util::funcToString(req->messages(0), true);
+
     int nMessages = req->messages_size();
 
     // Records for tests - copy messages before execution to avoid races
@@ -265,8 +266,8 @@ void Scheduler::executeBatch(std::shared_ptr<faabric::BatchExecuteRequest> req)
     // For threads we only need one executor, for anything else we want
     // one Executor per function in flight.
     if (isThreads) {
-        // Threads use the existing executor. We assume there's only
-        // one running at a time.
+        // Threads use the existing executor. There must only be one at a time,
+        // thus we use a function string that includes the app id
         std::vector<std::shared_ptr<faabric::executor::Executor>>&
           thisExecutors = executors[funcStr];
 
@@ -335,7 +336,7 @@ std::shared_ptr<faabric::executor::Executor> Scheduler::claimExecutor(
   faabric::Message& msg,
   faabric::util::FullLock& schedulerLock)
 {
-    std::string funcStr = faabric::util::funcToString(msg, false);
+    std::string funcStr = faabric::util::funcToString(msg, true);
 
     std::vector<std::shared_ptr<faabric::executor::Executor>>& thisExecutors =
       executors[funcStr];

src/util/func.cpp

@@ -24,7 +24,7 @@ std::string funcToString(const faabric::Message& msg, bool includeId)
     std::string str = msg.user() + "/" + msg.function();
 
     if (includeId) {
-        str += ":" + std::to_string(msg.id());
+        str += ":" + std::to_string(msg.appid());
     }
 
     return str;