I have been using my own command tool, Blowhole, to write log entries a lot over the last couple of days, while working on GCD code. Today I have spent several hours trying to trace a bug which was preventing my GCD app from writing messages to the log via Blowhole.
You may have had a similar experience. You know the code should work, but no matter which way you try to work around it, it doesn’t. In the end, I wondered whether there might be something wrong with Blowhole itself – and yes, in the undocumented changes which Apple made to Sierra’s log system in the 10.12.4 update, Blowhole 1.2 no longer works properly. This accompanies the other undocumented change, which renders log entries inaccessible unless you have admin privileges.
I do not know how extensive this change is, but it certainly affects Swift 3 code which tries to write integer values into log entries. Instead of the entries being written as they should, a log error is returned. Should you maintain any code which uses Sierra’s log, I strongly recommend that you check that it still works in 10.12.4. I have not had to change any of my code, simply rebuild the project.
So here is an updated version (1.3) of Blowhole. I have taken the opportunity of adding usage information with a new -h option: blowhole13
I do not know whether this version is backward compatible, so if you are running 10.12.3 or earlier, you may prefer to keep with version 1.2. I will leave both in the Downloads page above.