Enable SOCK_NONBLOCK on system call socket()

[panjf2000]

What this PR mainly does is:

1. Refactor the anetCreateSocket() to make it more generic for more socket arguments, and use SOCK_NONBLOCK if available, which will reduce two system calls (F_GETFL and F_SETFL) of enabling the non-blocking mode on each newly created socket.
2. Clean up the unused anetUnixGenericConnect() that calls anetCreateSocket().

SOCK_NONBLOCK for system call socket() is supported on most UNIX-like platforms (linux, dragonfly, freebsd, netbsd, openbsd, solaris, etc.). This improvement will significantly reduce the system calls considering how massively anetTcpGenericConnect() will be called when needed.

As for the cleanup, anetUnixGenericConnect was introduced in c61e692 and the only reference back then was from the createClient() in redis-benchmark.c which had been removed in ec8f066 and made it the dead code. Most of that dead code was also cleaned up in f657315, and it seems that the anetUnixGenericConnect got left out. Therefore, I also cleaned it up, but I'm not so certain about doing this cleanup in this PR. Maybe you would prefer to do it in a separate PR?

References

• socket(2) on Linux
• socket(2) on FreeBSD
• socket(2) on DragonFly
• socket(2) on NetBSD
• socket(2) on OpenBSD
• socket(3c) on Solaris
• socket(3socket) on illumos

[panjf2000]

@oranagra @yossigo

[panjf2000]

Kindly ping @oranagra @yossigo

[panjf2000]

Ping @oranagra @yossigo

[oranagra]

i'm confused.
why do we have to pass two different flags for the same purpose, rather than let anetCreateSocket handle it implicitly with ifdefs?
as far as i remember that was your previous approach, why did you abandon it?

[panjf2000]

since we do care about CLOEXEC for the listen sockets, maybe we should handle them like NONBLOCK REUSEADDR, and let anetCreateSocket get flags and handle them all internally?

Did I misunderstand your previous comment?

[oranagra]

maybe i misunderstood something and my comment isn't applicable..

when i gave that comment it was on a piece of code that explicitly called anetCloexec, and you added an #ifdef for SOCK_CLOEXEC, but code was far from the logical "#else. so i'm trying to suggest that all the logic about these 3 flags, (whether to pass them as flags to socketor call an explicit system call after it), should all be be hidden insideanetCreateSocket` that abstracts all the nuances about how to use the system calls.

i hope it's doable.

[panjf2000]

Please check out the latest commit.

[panjf2000]

@oranagra Any thoughts about the latest commit?

[panjf2000]

Ping @oranagra

[panjf2000]

Ping @oranagra

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