Unsafe: removing the monitorEnter/monitorExit/tryMonitorEnter methods

[Mandy Chung]

On 2/27/14 4:29 AM, Paul Sandoz wrote:
>> This will allocate about 10 Thread objects per second until the other thread finally reaches the synchronized read() method in BufferedInputStream...
>> >
> I like it.

I like it too.
> I do have a slight preference for Mandy's solution, see below, but i am not sure we can guarantee it is supported on all test platforms.

The hotspot VM implementation supports it on all platforms.  Note that 
this cost is not small - it stops the world and up call to JVM.

Mandy

>
> Paul.
>
>          try {
>              while (!isMonitorLockHeld(monitor)) {
>                  Thread.sleep(1);
>              }
>          } catch (UnsupportedOperationException e) {
>              // Back up plan?
>              Thread.sleep(TimeUnit.SECONDS.toMillis(1));
>          }
>
>      /**
>       * Returns {@code true} if and only if the a thread holds the
>       * monitor lock on the specified object.
>       *
>       * @throws java.lang.UnsupportedOperationException if monitoring of
>       * object monitor use is not supported
>       */
>      public static boolean isMonitorLockHeld(Object o) {
>          int oihc = System.identityHashCode(o);
>          ThreadMXBean tmxbean = ManagementFactory.getThreadMXBean();
>          ThreadInfo[] tinfos = tmxbean.dumpAllThreads(true, false);
>
>          for (ThreadInfo ti : tinfos) {
>              for (MonitorInfo mi : ti.getLockedMonitors()) {
>                  if (mi.getIdentityHashCode() == oihc)
>                      return true;
>              }
>          }
>          return false;
>      }
>