java/src/main/com/google/appengine/tools/development/InstanceStateHolder.java

   1 package com.google.appengine.tools.development;
   2
   3 import javax.annotation.concurrent.GuardedBy;
   4
   5 /**
   6  * Holder for the state of a server or backend instance.
   7  */
   8 public class InstanceStateHolder {
   9   static enum InstanceState {
  10     INITIALIZING, SLEEPING, RUNNING_START_REQUEST, RUNNING, STOPPED, SHUTDOWN;
  11   }
  12   private final String serverOrBackendName;
  13   private final int instance;
  14   @GuardedBy("this")
  15   private InstanceState currentState = InstanceState.SHUTDOWN;
  16
  17   /**
  18    * Constructs an {@link InstanceStateHolder}.
  19    *
  20    * @param serverOrBackendName For server instances the server name and for backend instances the
  21    *     backend name.
  22    * @param instance The instance number or -1 for load balancing servers and automatic servers.
  23    */
  24   InstanceStateHolder(String serverOrBackendName, int instance) {
  25     this.serverOrBackendName = serverOrBackendName;
  26     this.instance = instance;
  27   }
  28
  29   /**
  30    * Updates the current server state and verifies that the previous state is
  31    * what is expected.
  32    *
  33    * @param newState The new state to change to
  34    * @param acceptablePreviousStates Acceptable previous states
  35    * @throws IllegalStateException If the current state is not one of the
  36    *         acceptable previous states
  37    */
  38   synchronized void testAndSet(InstanceState newState,
  39       InstanceState... acceptablePreviousStates) throws IllegalStateException {
  40     if (test(acceptablePreviousStates)) {
  41       currentState = newState;
  42       return;
  43     }
  44     StringBuilder error = new StringBuilder();
  45     error.append("Tried to change state to " + newState);
  46     error.append(" on server " + serverOrBackendName + "." + instance);
  47     error.append(" but previous state is not ");
  48     for (int i = 0; i < acceptablePreviousStates.length; i++) {
  49       error.append(acceptablePreviousStates[i].name() + " | ");
  50     }
  51     throw new IllegalStateException(error.toString());
  52   }
  53
  54   /**
  55    * Returns true if current state is one of the provided acceptable states.
  56    */
  57   synchronized boolean test(InstanceState... acceptableStates) {
  58     for (InstanceState acceptable : acceptableStates) {
  59       if (currentState == acceptable) {
  60         return true;
  61       }
  62     }
  63     return false;
  64   }
  65
  66   /**
  67    * Checks if the server is in a state where it can accept incoming requests.
  68    *
  69    * @return true if the server can accept incoming requests, false otherwise.
  70    */
  71   synchronized boolean acceptsConnections() {
  72     return (currentState == InstanceState.RUNNING
  73         || currentState == InstanceState.RUNNING_START_REQUEST
  74         || currentState == InstanceState.SLEEPING);
  75   }
  76
  77   /**
  78    * Returns the display name for the current state.
  79    */
  80   synchronized String getDisplayName() {
  81     return currentState.name().toLowerCase();
  82   }
  83
  84   /**
  85    * Unconditionally sets the state.
  86    */
  87   synchronized void set(InstanceState newState) {
  88     currentState = newState;
  89   }
  90 }