Summary

The Synchrony process is killed, at random, usually after Confluence is running for a couple of days. As Confluence fails to restart the Synchrony process, Collaborative Editing stops working and the users can only edit pages after Collaborative Editing is disabled in the UI.

Synchrony can only be restarted by restarting Confluence.

Environment

• 7.1.1 - but can affect different Confluence versions after Synchrony was implemented (Confluence 6.0)
• Windows Server 

Diagnosis

Cannot enable Collaborative editing, as can be observed in the Synchrony logs:
<confluence-home>/logs/atlassian-synchrony.log

[plugins.synchrony.bootstrap.DefaultSynchronyProcessManager] startup Starting Synchrony and enabling Collaborative Editing
2020-10-15 12:23:46,193 DEBUG [synchrony-interop-executor:thread-1] [plugins.synchrony.utils.SynchronyProcessUtil] killRunningSynchronyProcess Reading C:\atlassian\confluence_server\temp\synchrony.pid
2020-10-15 12:23:46,349 ERROR [Long running task: Restart Synchrony Task] [plugins.synchrony.tasks.AbstractConfigLongRunningTask] runInternal An error occurred when running a Synchrony ConfigLongRunningTask
-- url: /rest/synchrony-interop/restart | referer: https://<confluence-baseurl>/admin/confluence-collaborative-editor-plugin/configure.action | traceId: 8bde67de28b99aec | userName: xxx
org.zeroturnaround.exec.InvalidExitValueException: Unexpected exit value: 1, allowed exit values: [0], executed command [taskkill, /F, /PID, 3052]
at org.zeroturnaround.exec.InvalidExitUtil.checkExit(InvalidExitUtil.java:27)
at org.zeroturnaround.exec.WaitForProcess.call(WaitForProcess.java:114)
at org.zeroturnaround.exec.ProcessExecutor.executeNoTimeout(ProcessExecutor.java:938)

In Confluence Administration Synchrony process is showing an error:

In some cases, Synchrony logs will not log anything since the Windows Update.

Cause

This entry normally indicates that Windows was unable to kill the old Synchrony process and returned this error message.

Solution

1. Stop Confluence
2. Open the file <Confluence-Install>\temp\synchrony.pid and take note of this ID
3. Open the task manager and go to the Details tab
4. Ensure no process is running with the noted PID from step 2, if you see one, stop it
5. Delete the file <Confluence-Install>\temp\synchrony.pid
6. Start Confluence
7. Check if the Synchrony process is started and Collaborative Editing feature is working as expected.