bpo-21302: Add nanosleep() implementation for time.sleep() in Unix by Livius90 · Pull Request #28526

bpo-21302: Add nanosleep() implementation for time.sleep() in Unix by Livius90 · Pull Request #28526 · python/cpython

Use nanosleep() for time.sleep() in Unix operation systems in case if clock_nanosleep() is not available but nanosleep() is available.

Some previous pull request history can be found here: #28111, #28341, #28483

nanosleep() is supported in the following operating systems: Linux (since 2001), FreeBSD (since 1997), OpenBSD (since 1997), NetBSD (since 1997), IBM AIX (since v7.1 2010), macOS (since OS X v10.9 2013)
clock_nanosleep() is supported in the following operating systems: Linux (since 2001), FreeBSD (since 2008), NetBSD (since 2014), IBM AIX (since v7.1 2010)

https://bugs.python.org/issue21302

Replace outdated select() to use nanosleep() for sleep implementation in Unix

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I would prefer to restrict this PR to using nanosleep() in time.sleep(), and nothing else. IMO it's already complex enough :-)


		do {
		#ifndef HAVE_CLOCK_NANOSLEEP
		#if defined(HAVE_NANOSLEEP) && !defined(HAVE_CLOCK_NANOSLEEP)

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The change LGTM, but I propose to write the #ifdef dance differently and rename secs to timeout to make the code more readable. I created PR #28545 based on your PR. Is it better? For the main code in Py_BEGIN_ALLOW_THREADS/Py_END_ALLOW_THREADS, I merged the 3 code paths to put if #ifdef in the Py_BEGIN_ALLOW_THREADS block. What do you think?