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Host contract: the runtime flips the PROCESS's SIGPIPE to SIG_IGN on the first proc_spawn (and on http bind) and never restores it; print ignores flush errors, so a pipeline into head runs to completion and exits 0

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
48/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Active
Tech stack
c
Domain
operating-systems

Research direction

Start with the probe files in ~/src/wt/briefs/conc-review/probes-{A,B,C}/ and inspect proc_install_sigpipe_ignore in src/builtins_host.c, http_early_bind/http_serve in src/ext_http.c, and print in src/builtins.c. Reproduce the pipeline behavior, then verify that writes no longer change the host's SIGPIPE disposition, print handles flush errors, and eigs_embed.h documents remaining process-global dispositions.

Written by the indexing model from the issue text.

Description

area:runtime-vm bug

Found by the 2026-09-14 whole-runtime concurrency review (three independent reviewers, every finding below reproduced by execution on main @ a18deac unless marked reading). Probe files live in ~/src/wt/briefs/conc-review/probes-{A,B,C}/.

proc_install_sigpipe_ignore src/builtins_host.c:1437-1438 via pthread_once :1465; http_early_bind/http_serve do the same unconditionally (src/ext_http.c:604, :1792). print is fflush(stdout) with no error check (src/builtins.c:78-209).

Observed

p is proc_spawn of (["true"])
i is 0
loop while i < 200000:
    print of f"line {i}"
    i is i + 1

… | head -1: control (no spawn) rc=141 (SIGPIPE) in 0.03 s; with the spawn rc=0 in 0.59 s, stderr empty — 200k prints into a closed pipe, silently. For an embedder, the first subprocess or HTTP bind replaces the host's own SIGPIPE disposition process-wide; eigs_embed.h says nothing (SIGUSR1 is CLI-only, src/main.c:169-174).

Fix direction

Per-write suppression (MSG_NOSIGNAL on sockets; for pipes, block/unblock SIGPIPE around the write or use a save/restore) instead of a process-wide flip; make print check the flush and raise or exit on EPIPE; document the remaining process-global dispositions in eigs_embed.h.

Dominant language
C
Stars
3
Forks
7
Avg merge
3h 58m
Merged PRs (30d)
105

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