[Unix] Forward signals to pre-installed handlers + add --handle-signals=minimal#61294
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[Unix] Forward signals to pre-installed handlers + add --handle-signals=minimal#61294topolarity wants to merge 3 commits intoJuliaLang:masterfrom
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In theory, this significantly improves our Julia-as-a-library behavior by allowing Julia to forward signals to other copies of the Julia runtime, or an outer application that may have loaded us. Covers all fault handlers: SIGSEGV, SIGBUS, SIGFPE, SIGILL, SIGABRT, SIGSYS, SIGTRAP as well as SIGUSR2 Also adds forwarding for SIGINT, SIGTERM, SIGQUIT, SIGINFO, and SIGUSR1 although these `sigwait()`'d signals will typically be blocked anyway so that forwarding will not happen.
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This adds a `--handle-signals=minimal` option to restrict Julia to installing only those signals that are essential to its operation and which we can reliably forward to outer / pre-existing handlers. The signals excluded are generally the "I/O"-like signals, incl. SIGINT, SIGUSR1/2, SIGINFO, and SIGTERM / SIGQUIT and received by `sigwait()` which cannot forward signals to a competing `sigwait()` loop anyway. For an end user, this means that Julia will not respond to `Ctrl-C`, SIGTERM / SIGQUIT (requests to terminate), or support in-process profiling. This is appropriate behavior for a library, which should typically defer these signals to the overall application anyway.
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This test checks the "sweet spot" we're interested in: - Installed handlers can reliably forward signals - Installed handlers are sufficient for GC + multi-threading --------- Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
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This adds a
--handle-signals=minoption to restrict Julia to installing only those signals that are:The most important of these is our SIGSEGV / SIGBUS handler (used by the GC as a safepoint trigger), but this also changes divide-by-zero, SIGILL, and similar faults to prefer forwarding these to a previously installed handler, if one was found, rather than immediately throwing an exception in Julia.
This is intended to be used in a "Julia as a library" scenario.
From a user's perspective the limitations of "minimal" signal handling are:
Ctrl-CsignalsProfile.@profile) is not supportedSIGTERM/SIGQUITDivideError(and similar) exceptions despite triggering a faultIn the future, it may be a good idea to keep a stricter notion of "execution state" on each thread, so that Julia can distinguish, e.g., a
DivideErrorfault in its own code vs. faults in other libraries (or parallel copies of the Julia runtime).Python handles this "thread attach / detach" via
PyGILState_Ensure/PyGILState_Releaseand Java does this viaAttachCurrentThread/DetachCurrentThreadand of course Windows has the SEH stack but the Julia API has no equivalent (jl_adopt_thread/jl_destroy_threadare called based on the thread lifetime, not the active execution state).P.S. This is Linux / BSD-only as is. macOS will need additional work, since forwarding mach exceptions is somewhat more complicated.
Co-developed with Claude.