[issue45251] signal.SIGCLD alias is not available on OSX

[Terry J. Reedy]

Change by Terry J. Reedy :


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versions:  -Python 3.6, Python 3.7, Python 3.8

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[issue45251] signal.SIGCLD alias is not available on OSX

[Ronald Oussoren]

Ronald Oussoren  added the comment:

The documentation for the SIG* constants also mentions:


SIG*
All the signal numbers are defined symbolically. For example, the hangup signal 
is defined as signal.SIGHUP; the variable names are identical to the names used 
in C programs, as found in . The Unix man page for ‘signal()’ lists 
the existing signals (on some systems this is signal(2), on others the list is 
in signal(7)). Note that not all systems define the same set of signal names; 
only those names defined by the system are defined by this module.


This is however mentioned halfway through the list of constants.  I'm not sure 
why this is so, IMHO it would be clearer to move the fragment I quote to the 
start of the module constants section.

We shouldn't define SIGCLD on platforms that don't have this name available in 
their libc headers, which includes macOS.  If the fragment above were moved to 
the start of the section no further updates would be required (IMHO).

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components: +macOS
nosy: +ned.deily, ronaldoussoren

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[issue45251] signal.SIGCLD alias is not available on OSX

[Thomas Caswell]

New submission from Thomas Caswell :

The module attribute signal.SIGCLD 
(https://docs.python.org/3/library/signal.html#signal.SIGCLD) is an "archaic" 
(quoting from the GNU C Library source) alias for signal.SIGCHLD 
(https://docs.python.org/3/library/signal.html#signal.SIGCHLD). signal.SIGCHLD 
is documented as being available on unix, and signal.SIGCLD is documented as an 
alias of signal.SIGCHLD.  

However, it seems that clang does not define the SIGCLD back-compatibility name 
[1] so the SIGCLD alias is missing on OSX (all the way to at least 2.7) because 
the clang headers appear to not define the SIGCLD macro and hence the logic in 
modulesignal.c does not find it, and hence the rest of the tooling in signal.py 
does not find it.

I am not sure if the correct fix is to document that SIGCLD in only available 
on linux (which I am not sure is completely correct, maybe "availability is 
platform dependent, but definitely not on darwin"?) or to add the macro if 
SIGCHLD is defined and SIGCLD is missing (see attached patch)

[1] SIGCLD is not documented in 
https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man3/signal.3.html
 and not the signal.h that ships with xcode

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assignee: docs@python
components: Documentation, Library (Lib)
files: osx_signal_compat.patch
keywords: patch
messages: 402280
nosy: docs@python, tcaswell
priority: normal
severity: normal
status: open
title: signal.SIGCLD alias is not available on OSX
versions: Python 3.10, Python 3.11, Python 3.6, Python 3.7, Python 3.8, Python 
3.9
Added file: https://bugs.python.org/file50290/osx_signal_compat.patch

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