Add socket.getblocking() method

[1st1]

BPO	32373
Nosy	@pitrou, @vstinner, @njsmith, @asvetlov, @1st1
PRs	bpo-32373: Add socket.getblocking() method. #4926

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/1st1'
closed_at = <Date 2018-01-28.23:18:40.694>
created_at = <Date 2017-12-19.14:23:24.198>
labels = ['3.7', 'type-feature', 'library']
title = 'Add socket.getblocking() method'
updated_at = <Date 2018-01-28.23:18:40.693>
user = 'https://github.com/1st1'

bugs.python.org fields:

activity = <Date 2018-01-28.23:18:40.693>
actor = 'yselivanov'
assignee = 'yselivanov'
closed = True
closed_date = <Date 2018-01-28.23:18:40.694>
closer = 'yselivanov'
components = ['Library (Lib)']
creation = <Date 2017-12-19.14:23:24.198>
creator = 'yselivanov'
dependencies = []
files = []
hgrepos = []
issue_num = 32373
keywords = ['patch']
message_count = 6.0
messages = ['308645', '308656', '308658', '308663', '308693', '311019']
nosy_count = 5.0
nosy_names = ['pitrou', 'vstinner', 'njs', 'asvetlov', 'yselivanov']
pr_nums = ['4926']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue32373'
versions = ['Python 3.7']

[1st1]

Currently we have the following methods:

• socket.settimeout(t) -- can set the socket in blocking mode, when t==0.
• socket.setblocking(flag) -- sets in blocking or non-blocking mode.
• socket.gettimeout() -- returns 0 when socket is in non-blocking mode.

socket.gettimeout() is the only easy way of checking if the socket is non-blocking or blocking, but it's not intuitive to use it. It's especially strange that we have a setblocking() method without a corresponding getblocking().

I propose to add a 'socket.getblocking() -> bool' method.

[1st1]

It looks like we have a bug with 'sock.settimeout()' and non-blocking/blocking modes (or maybe this is a feature?)

Currently:

• to make a socket non-blocking, we call 'sock.settimeout(0)'.

• to make a socket blocking, we call 'sock.settimeout(None)'.

What happens if we call sock.settimeout(t), where t > 0? The internal timeout field of the socket object will simply be set to 't'. What happens if the socket was in a non-blocking mode? Nothing, it stays in non-blocking mode.

What it means: suppose you have a non-blocking socket. You call socket.settimeout(10), and most likely you wanted to make it blocking again. Because all operations on the socket become blocking from moment (sock_call_ex repeats on EWOULDBLOCK and EAGAIN).

Now is having a timeout and blocking send/recv methods on a non-blocking socket a feature? Or is this a bug?

[pitrou]

Now is having a timeout and blocking send/recv methods on a non-blocking socket a feature? Or is this a bug?

I agree it's a bug (but should only be fixed in 3.7).

Also I agree with adding a socket.getblocking() method.

[asvetlov]

Agree, it's a bug.

+1 for getblocking()

[1st1]

It appears the the timeouts situation is a bit more complex. It's perfectly normal for a Python socket object to be in a "blocking" mode and for its FD to be in a non-blocking mode. Read more about this in the latest docs update to the PR: adcc91f

[1st1]

New changeset f11b460 by Yury Selivanov in branch 'master':
bpo-32373: Add socket.getblocking() method. (bpo-4926)
f11b460