0
@@ -54,11 +54,23 @@ explicitly define some special types:
0
     inactive_apps. This iterator is only valid if this AppContainer really is
0
     in that list.
0
 
0
+=== Special functions
0
+
0
+- spawn(app_root)
0
+  Spawns a new instance of the application at the given application root.
0
+  Throws an exception if something went wrong. This function is thread-safe.
0
+  Note that application initialization can take an arbitrary amount of time.
0
+
0
 === Instance variables
0
 
0
 The algorithm requires the following instance variables for storing state
0
 information:
0
 
0
+- lock: mutex
0
+  This lock is used for implementing thread-safetiness. We assume that it
0
+  is non-recursive, i.e. if a thread locks a mutex that it has already locked,
0
+  then it will result in a deadlock.
0
+
0
 - apps: map[string => list<AppContainer>]
0
   Maps an application root to a list of AppContainers. Thus, this map contains
0
   all application instances that are in the pool.
0
@@ -107,10 +119,6 @@ information:
0
 == Algorithm in pseudo code
0
 
0
 # Thread-safetiness notes:
0
-# - The following functions are to be run inside the same lock:
0
-#   * get()
0
-#   * session_has_been_closed()
0
-#   * The cleaner thread's main function.
0
 # - All wait commands are to unlock the lock during waiting.
0
 
0
 function get(app_root):
0
@@ -118,23 +126,24 @@ function get(app_root):
0
   attempt = 0
0
   while (true):
0
     attempt++
0
-		container, list = spawn_or_use_existing(app_root)
0
-		container.last_used = current_time()
0
-		container.sessions++
0
-		try:
0
-			return container.app.connect()
0
-		on exception:
0
-			container.sessions--
0
-			if (attempt == MAX_ATTEMPTS):
0
-				propagate exception
0
-			else:
0
-				# The app instance seems to have crashed. So we remove this
0
-				# instance from our data structures.
0
-				list.remove(container.iterator)
0
-				if list.empty():
0
-					apps.remove(app_root)
0
-				count--
0
-				active--
0
+		lock.synchronize:
0
+			container, list = spawn_or_use_existing(app_root)
0
+			container.last_used = current_time()
0
+			container.sessions++
0
+			try:
0
+				return container.app.connect()
0
+			on exception:
0
+				container.sessions--
0
+				if (attempt == MAX_ATTEMPTS):
0
+					propagate exception
0
+				else:
0
+					# The app instance seems to have crashed. So we remove this
0
+					# instance from our data structures.
0
+					list.remove(container.iterator)
0
+					if list.empty():
0
+						apps.remove(app_root)
0
+					count--
0
+					active--
0
 
0
 
0
 # Returns a pair of [AppContainer, list<AppContainer>] that matches the
0
@@ -207,7 +216,7 @@ function spawn_or_use_existing(app_root):
0
     container = new AppContainer
0
     # TODO: we should unlock the mutex during spawning,
0
     # and add some kind of timeout check.
0
-		container.app = spawn(app)
0
+		container.app = spawn(app_root)
0
     container.sessions = 0;
0
     list = apps[app_root]
0
     if list == nil:
0
@@ -224,14 +233,15 @@ function spawn_or_use_existing(app_root):
0
 # _container_ is the AppContainer that contains the application for which a
0
 # session has been closed.
0
 function session_has_been_closed(container):
0
-	list = apps[container.app.app_root]
0
-	if list != nil:
0
-		container.last_used = current_time()
0
-		container.sessions--
0
-		if container.sessions == 0:
0
-			list.move_to_front(container.iterator)
0
-			container.ia_iterator = inactive_apps.add_to_back(container.app)
0
-		active--
0
+	lock.synchronize:
0
+		list = apps[container.app.app_root]
0
+		if list != nil:
0
+			container.last_used = current_time()
0
+			container.sessions--
0
+			if container.sessions == 0:
0
+				list.move_to_front(container.iterator)
0
+				container.ia_iterator = inactive_apps.add_to_back(container.app)
0
+			active--
0
 
0
 
0
 function needs_restart(app_root):
0
@@ -258,22 +268,23 @@ function needs_restart(app_root):
0
 # The following thread will be responsible for cleaning up idle application
0
 # instances, i.e. instances that haven't been used for a while.
0
 thread cleaner:
0
-	done = false
0
-	while !done:
0
-		Wait until CLEAN_INTERVAL seconds have expired, or until the thread has been signalled to quit.
0
-		if thread has been signalled to quit:
0
-			done = true
0
-			break
0
+	lock.synchronize:
0
+		done = false
0
+		while !done:
0
+			Wait until CLEAN_INTERVAL seconds have expired, or until the thread has been signalled to quit.
0
+			if thread has been signalled to quit:
0
+				done = true
0
+				break
0
     
0
-		now = current_time()
0
-		for all container in inactive_apps:
0
-			app = container.app
0
-			app_list = apps[app.app_root]
0
-			if now - container.last_used > MAX_IDLE_TIME:
0
-				app_list.remove(container.iterator)
0
-				inactive_apps.remove(iterator for container)
0
-				count--
0
-			if app_list.empty():
0
-				apps.remove(app.app_root)
0
-				restart_file_times.remove(app.app_root)
0
+			now = current_time()
0
+			for all container in inactive_apps:
0
+				app = container.app
0
+				app_list = apps[app.app_root]
0
+				if now - container.last_used > MAX_IDLE_TIME:
0
+					app_list.remove(container.iterator)
0
+					inactive_apps.remove(iterator for container)
0
+					count--
0
+				if app_list.empty():
0
+					apps.remove(app.app_root)
0
+					restart_file_times.remove(app.app_root)
0
 

0
@@ -557,7 +557,6 @@ public:
0
   
0
   virtual Application::SessionPtr
0
   get(const string &appRoot, bool lowerPrivilege = true, const string &lowestUser = "nobody") {
0
-		mutex::scoped_lock l(lock);
0
     unsigned int attempt;
0
     const unsigned int MAX_ATTEMPTS = 5;
0
     
0
@@ -565,6 +564,7 @@ public:
0
     while (true) {
0
       attempt++;
0
       
0
+			mutex::scoped_lock l(lock);
0
       pair<AppContainerPtr, AppContainerList *> p(
0
         spawnOrUseExisting(l, appRoot, lowerPrivilege, lowestUser)
0
       );