Avoid traversing ocaml objects when not holding the runtime lock in spawn_unix
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This helps ensure the stability of existing behavior in light of the upcoming bugfix to `spawn_unix`. Signed-off-by: Nick Roberts <nroberts@janestreet.com>
Avoid traversing OCaml data structures when the runtime lock is not held. Signed-off-by: Nick Roberts <nroberts@janestreet.com>
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mshinwell
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Jul 3, 2024
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| sigprocmask_command = Long_val(v_sigprocmask_command); | ||
| sigprocmask_signals_length = Wosize_val(v_sigprocmask_signals); | ||
| sigprocmask_signals = (int*)malloc(sizeof(int) * sigprocmask_signals_length); |
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Need to check return value from malloc
| break; | ||
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| default: | ||
| caml_failwith("Unknown sigprocmask action"); |
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Can't call caml_failwith in this context -- need caml_leave_blocking_section (etc) first. See the cleanup when safe_pipe fails above.
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Whoops, it's as if I've never read the patch. This makes me convinced that we should split the file in two files:
- the part with bindings that runs with OCaml lock held
- the part with thread-safe code that doesn't even include any of the OCaml headers
I'll prepare a feature that does that.
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(Don’t be too hard on yourself — the failwith was there before. GitHub is just doing a bad job showing changed code, thus revealing bugs nearby.)
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sigprocmaskinto C data structures before releasing the runtime lock inspawn_unix.This fixes a possible bad interaction with the GC. When the runtime lock isn't held by the current thread, another OCaml thread could run the GC and thus move around OCaml heap objects.
The PR takes the approach described in the C FFI section of the OCaml manual:
("entering a blocking section" is the same thing as "releasing the runtime system".)