I believe that I discovered a nasty little race condition in the
org.jmol.viewer.ScriptManager class, which rears its head when
multiple calls to JMolViewer.script() are made in rapid
succession. Obviously, this is most likely to occur when using
JMolViewer programmatically, rather than from JavaScript (since
JavaScript is too slow to call frequently enough).
In any case, the problem is that the ScriptManager.addScript() method
first checks to see if the script execution thread is running; if
not, it starts it. The problem is that if two calls to addScript are
made in rapid succession, multiple threads can be created, and the
resulting scripts are run multiple times. Not good!
The solution is to move the setting of scriptQueueRunning = true from
the run() method of ScriptQueueRunnable to the start ScriptQueue
function itself. This eliminates the problem.
private void startScriptQueue() {
if (scriptQueueRunning)
return;
scriptQueueRunning = true; <- set it here!
queueThread = new Thread(new ScriptQueueRunnable());
queueThread.start();
}
The astute coder may not that this doesn't actually eliminate the
race condition, it just mitigates it. There is still a race
condition between the check in the if statement and the setting of
the variable. I think (but I haven't verified) that this can be
eliminated with a synchronized block, like
private void startScriptQueue() {
synchronized(this) {
if (scriptQueueRunning)
return;
scriptQueueRunning = true; <- set it here!
}
queueThread = new Thread(new ScriptQueueRunnable());
queueThread.start();
}
I don't have SVN write access, so I'll leave the final solution to
one of you fine fellows.
JR Schmidt
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