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The SIGCHLD handler reaps every child with waitpid(-1) and queues the statuses. That breaks any other party managing children in the same process: HPC-GAP's signal thread (issue #5), and programs embedding GAP such as julia, whose libuv reaps its subprocesses per pid and hangs forever once io has stolen a status (GAP.jl#902). In those two settings install no handler; instead keep a registry of the children created by IO_fork and wait for them with waitpid(pid), on demand. IO_IgnorePid marks a registered child to be reaped whenever io next deals with children, and IO_WaitPid(-1, ...) polls the registry. Standalone GAP keeps the handler and the FIFO unchanged. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
fingolfin
commented
Sep 8, 2026
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Member
|
So I'm happy with this. I remember (but I've forgotten the details!) that how io an gap core handle children was a bit of a mess, and it's hard to pick apart, but there are tests which should catch obvious breakage (like never cleaning up any children) |
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The SIGCHLD handler reaps every child with waitpid(-1) and queues the statuses. That breaks any other party managing children in the same process: HPC-GAP's signal thread (issue #5), and programs embedding GAP such as julia, whose libuv reaps its subprocesses per pid and hangs forever once io has stolen a status (GAP.jl#902).
In those two settings install no handler; instead keep a registry of the children created by IO_fork and wait for them with waitpid(pid), on demand. IO_IgnorePid marks a registered child to be reaped whenever io next deals with children, and IO_WaitPid(-1, ...) polls the registry. Standalone GAP keeps the handler and the FIFO unchanged.
Co-Authored-By: Claude Fable 5.1 noreply@anthropic.com
CC @lgoettgens
Progress towards issue #5 (I am not sure when exactly we can declare that one to be resolved)