Fix race condition in standard_error process registration #10290
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CT Test Results 2 files 72 suites 1h 11m 31s ⏱️ For more details on these failures, see this check. Results for commit 6b6f7f9. ♻️ This comment has been updated with latest results. To speed up review, make sure that you have read Contributing to Erlang/OTP and that all checks pass. See the TESTING and DEVELOPMENT HowTo guides for details about how to run test locally. Artifacts
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josevalim
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Oct 22, 2025
Fix a race condition where the standard_error process could call prim_tty:init/1 before being registered, causing a crash when prim_tty's writer and reader processes attempt to derive their own registered names from the parent process. The issue was introduced in commit ead7424 (PR erlang#9116), which changed prim_tty's reader and writer processes to dynamically derive their registered names from their parent process name (e.g., 'standard_error' -> 'standard_error_reader', 'standard_error_writer'). This was done to support multiple TTY instances (stdout and stderr) with distinct process names. However, the standard_error:start/0 function had a race condition: 1. spawn(fun server/0) - creates process, starts executing immediately 2. register(?NAME, Id) - parent registers the spawned process 3. server() calls prim_tty:init() - may execute before step 2 When prim_tty:init/1 spawns writer/reader processes, they call set_name(Parent, Postfix) which does: erlang:process_info(Parent, registered_name) If this executes before the parent completes registration, it returns [] instead of {registered_name, standard_error}, causing a pattern match failure: "no match of right hand side value: []" at prim_tty.erl:674. The fix moves the register/2 call into the spawned process itself, ensuring it completes before prim_tty:init/1 is called. This eliminates the race condition entirely. Closes erlang#10174
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Fix a race condition where the standard_error process could call prim_tty:init/1 before being registered, causing a crash when prim_tty's writer and reader processes attempt to derive their own registered names from the parent process.
The issue was introduced in commit ead7424 (PR #9116), which changed prim_tty's reader and writer processes to dynamically derive their registered names from their parent process name (e.g.,
standard_error->standard_error_reader,standard_error_writer). This was done to support multiple TTY instances (stdout and stderr) with distinct process names.However, the
standard_error:start/0function had a race condition:spawn(fun server/0)- creates process, starts executing immediatelyregister(?NAME, Id)- parent registers the spawned processserver()callsprim_tty:init()- may execute before step 2When
prim_tty:init/1spawns writer/reader processes, they callset_name(Parent, Postfix)which does:erlang:process_info(Parent, registered_name)If this executes before the parent completes registration, it returns [] instead of {registered_name, standard_error}, causing a pattern match failure: "no match of right hand side value: []" at prim_tty.erl:674.
The fix moves the
register/2call into the spawned process itself, ensuring it completes beforeprim_tty:init/1is called. This eliminates the race condition entirely.Closes #10174
For the record, this bug prevents the VM from starting altogether in a dockerised deployment at my workplace and we've had to stick to 27.x so far.