hs.ipc: Avoid reentrance when in printReplacement #3718
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hs.ipc replaces the print function with one that calls the original,
but also sends anything that print prints to any of the remote
connections. If you have debugging enabled, that means that the moment
the remote connection is created, a bunch of print statements are sent
to the this connection.
The problem I had is that my use of hs (command) was simply to send a
message to the screen:
warning () {
hs -c "hs.alert.show('$1')" > /dev/null
echo "$1"
}
The connection was so ephemeral, than I frequently got errors (related
to the client no long existing) which were tried to be send to the
client... so I ended with the following messages:
2023-12-31 22:00:02: 22:00:02 ERROR: LuaSkin: hs.ipc callback is
being called recursively. Check your callback function, it is
triggering further IPC messages. This message was triggered after
reaching 5 recursive callbacks.
This code avoid recursion for the same IPC client by keeping a counter
of how many times the client has entered the critical region.
Improved comments and identifiers of code that restricts printReplacement to reenter when it is already inside a print from a specific client.
![github-actions[bot]](https://avatars.githubusercontent.com/in/15368?s=60&v=4){kind=small}
Codecov ReportAll modified and coverable lines are covered by tests ✅
Additional details and impacted files@@ Coverage Diff @@
## master #3718 +/- ##
==========================================
+ Coverage 27.37% 27.42% +0.04%
==========================================
Files 191 191
Lines 51407 51407
==========================================
+ Hits 14074 14098 +24
+ Misses 37333 37309 -24 |
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when hs.ipc is enabled, print is replaced with printReplacement. The idea is to make sure that prints are sent to both the console and the client.
The problem arises when the client stops responding (either it is dead or it is taking time to respond). In that case, an error is generated, and a print is issued with the error/warning. Thus printReplacement is called again. This can go until HS detects the recursion and stops it. In some cases, this might cause crashes.
See this thread for context: https://groups.google.com/g/hammerspoon/c/dMH-exXe6ng
This code restricts printReplacement to never send a message while it is inside already of printReplacement for that particular client ID.
It is implemented by using a table indexed by the client ID. To avoid the table to grow forever, once a client ID counter is zero, it is removed from the table.