392 

   393   // Returns true if the current GC supports control of its concurrent

   394   // phase via requestConcurrentGCPhase().  If false, a request will

   395   // always fail.

   396   public native boolean supportsConcurrentGCPhaseControl();

   397 

   398   // Returns an array of concurrent phase names provided by this

   399   // collector.  These are the names recognized by

   400   // requestConcurrentGCPhase().

   401   public native String[] getConcurrentGCPhases();

   402 

   403   // Attempt to put the collector into the indicated concurrent phase,

   404   // and attempt to remain in that state until a new request is made.

   405   //

   406   // Returns immediately if already in the requested phase.

   407   // Otherwise, waits until the phase is reached.

   408   //

   409   // Throws IllegalStateException if unsupported by the current collector.

   410   // Throws NullPointerException if phase is null.

   411   // Throws IllegalArgumentException if phase is not valid for the current collector.

   412   public void requestConcurrentGCPhase(String phase) {

   413     if (!supportsConcurrentGCPhaseControl()) {

   414       throw new IllegalStateException("Concurrent GC phase control not supported");

   415     } else if (phase == null) {

   416       throw new NullPointerException("null phase");

   417     } else if (!requestConcurrentGCPhase0(phase)) {

   418       throw new IllegalArgumentException("Unknown concurrent GC phase: " + phase);

   419     }

   420   }

   421 

   422   // Helper for requestConcurrentGCPhase().  Returns true if request

   423   // succeeded, false if the phase is invalid.

   424   private native boolean requestConcurrentGCPhase0(String phase);