[SOLR-13408] Cannot start/stop DaemonStream repeatedly, other API improvements

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 7.7, 8.0, 9.0
• Fix Version/s: 7.7.2, 8.1, 9.0
• Component/s: streaming expressions
• Assignee: Erick Erickson
• Reporter: Erick Erickson
• Created: 16/Apr/19 02:01
• Updated: 08/Oct/19 14:50
• Resolved: 17/Apr/19 23:52

Description

If I create a DaemonStream then use the API commands to stop it then start it repeatedly, after the first time it's stopped/started, it cannot be stopped again.

DaemonStream.close() checks whether a local variable "closed" is true, and if so does nothing. Otherwise it closes the stream then sets "closed" to true.

However, when the stream is started again, "closed" is not set to false, therefore the next time you try to stop the deamon, nothing happens and it continues to run. One other consequence of this is that you can have orphan threads running in the background. Say I

stop the daemon
start it again
create another one with the same ID

When the new one is created, this code is executed over in StreamHandler.handleRequestBody:

daemons.remove(daemonStream.getId()).close();

which will not terminate the stream thread as above. Then the open() method executes this:

this.streamRunner = new StreamRunner(runInterval, id);

leaving the thread running.

Finally, there's an NPE if I try to start a non-existent daemon.