Timer replacement for Appengine

[Zero Trick Pony via StackOverflow]

To answer your question as asked:

I just found out that appengine does not allow timers! Why??

java.util.Timer is implemented using a Thread, which AppEngine does not allow except using its own API. So when you try to use java.util.Timer, you get an exception:

java.security.AccessControlException: access denied ("java.lang.RuntimePermission" "modifyThreadGroup")
    at java.security.AccessControlContext.checkPermission(AccessControlContext.java:375)
    at java.security.AccessController.checkPermission(AccessController.java:565)
    at java.lang.SecurityManager.checkPermission(SecurityManager.java:549)
    at com.google.apphosting.runtime.security.CustomSecurityManager.checkPermission(CustomSecurityManager.java:56)
    at com.google.apphosting.runtime.security.CustomSecurityManager.checkAccess(CustomSecurityManager.java:131)
    at java.lang.ThreadGroup.checkAccess(ThreadGroup.java:315)
    at java.lang.Thread.init(Thread.java:378)
    at java.lang.Thread.<init>(Thread.java:432)
    at java.util.TimerThread.<init>(Timer.java:499)
    at java.util.Timer.<init>(Timer.java:101)
    at java.util.Timer.<init>(Timer.java:132)

Disallowing arbitrary thread creation makes it easier for the AppEngine system to manage multiple applications on the same machine without interfering with each other too much.

AppEngine is offering a new service called "Managed VMs" which will allow any environment you want, including a full JVM that can have background threads: https://developers.google.com/appengine/docs/managed-vms/

Note that this API is currently in "preview" which means it is not yet recommended for reliable production use.

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http://stackoverflow.com/questions/13421872/timer-replacement-for-appengine/24621725#24621725