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net: Replace cs_feeFilter with simple std::atomic#18819

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fanquake merged 1 commit intobitcoin:masterfrom
maflcko:2004-netNoRecursiveMutex
Jan 11, 2021
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net: Replace cs_feeFilter with simple std::atomic#18819
fanquake merged 1 commit intobitcoin:masterfrom
maflcko:2004-netNoRecursiveMutex

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@maflcko maflcko commented Apr 29, 2020 •
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A RecursiveMutex is overkill for setting or reading a plain integer. Even a Mutex is overkill, when a plain std::atomic can be used.

This removes 11 lines of code. Also, it is cutting down on the number of locks put on the stack at the same time, which complicates review looking out for potential lock contention.

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laanwj commented Apr 30, 2020

Not sure if we care about this case, but this adds a strict assumption that CAmount is a typedef of an primitive integer type.

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maflcko commented Apr 30, 2020

Yeah, I thought about making a simple setter/getter to not leak the std::atomic implementation detail from net to net_processing, but that seemed over-engineering that can be done when it is needed.

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hebasto commented Apr 30, 2020 •
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Not sure if we care about this case, but this adds a strict assumption that CAmount is a typedef of an primitive integer type.

This assumption is already used:

bitcoin/src/qt/bitcoin.cpp

Lines 442 to 443 in e5b9308

// IMPORTANT: if CAmount is no longer a typedef use the normal variant above (see https://doc.qt.io/qt-5/qmetatype.html#qRegisterMetaType-1)
qRegisterMetaType<CAmount>("CAmount");

But I'd not exposing CAmount implementation details.

Concept ~0.

EDIT: I've reconsidered this pull.

@maflcko maflcko changed the title net: Remove unused cs_feeFilter net: Replace cs_feeFilter with simple std::atomic May 1, 2020
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Light tested ACK fa321c4afe.

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maflcko commented May 4, 2020

But I'd not exposing CAmount implementation details.

@hebasto I can't parse this sentence. Mind to explain? We already assume that the type is CAmount everywhere. The only thing this pull changes is removing a bunch of boilerplate code used for overkill locking behavior.

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laanwj commented May 4, 2020

Unless a performance improvement can be demonstrated I'm not sure this change is really worth it.

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maflcko commented May 4, 2020

It is mostly about the removed code (11 lines), and cutting down on the number of locks put on the stack at the same time, which complicates review looking out for potential lock contention.

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maflcko commented May 4, 2020

Performance wise this should have no effect. Reading from the mempool is orders of magnitude slower than taking a lock on a recursive mutex (even with lock contention debugging enabled).

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hebasto commented May 5, 2020

But I'd not exposing CAmount implementation details.

@hebasto I can't parse this sentence. Mind to explain? We already assume that the type is CAmount everywhere. The only thing this pull changes is removing a bunch of boilerplate code used for overkill locking behavior.

@MarcoFalke Apologies for my confusing comment.
I forgot that std::atomic template may be instantiated with any suitable type, not only with built-in ones (typedef of what CAmount currently is).

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DrahtBot commented May 27, 2020 •
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The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

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No conflicts as of last run.

@maflcko maflcko force-pushed the 2004-netNoRecursiveMutex branch from fa321c4 to fa3c2c2 Compare June 8, 2020 14:57
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maflcko commented Jun 9, 2020

Rebased

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ACK fa3c2c2, I have reviewed the code and it looks OK, I agree it can be merged.

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jnewbery commented Nov 7, 2020

utACK fa3c2c2

All this stuff should move to Peer in net_processing, but there's no harm simplifying it where it is now.

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@DrahtBot DrahtBot mentioned this pull request Jan 6, 2021
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@maflcko maflcko force-pushed the 2004-netNoRecursiveMutex branch from fa3c2c2 to fad1f0f Compare January 7, 2021 14:31
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maflcko commented Jan 7, 2021

Rebased due to trivial conflict in adjacent line

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jnewbery commented Jan 7, 2021

utACK fad1f0f

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practicalswift commented Jan 10, 2021

cr ACK fad1f0f: patch looks correct

@fanquake fanquake merged commit c4458cc into bitcoin:master Jan 11, 2021
sidhujag pushed a commit to syscoin/syscoin that referenced this pull request Jan 11, 2021
@fanquake
Merge bitcoin#18819: net: Replace cs_feeFilter with simple std::atomic
2b9456b 
fad1f0f net: Remove unused cs_feeFilter (MarcoFalke)

Pull request description:

  A `RecursiveMutex` is overkill for setting or reading a plain integer. Even a `Mutex` is overkill, when a plain `std::atomic` can be used.

  This removes 11 lines of code. Also, it is cutting down on the number of locks put on the stack at the same time, which complicates review looking out for potential lock contention.

ACKs for top commit:
  jnewbery:
    utACK fad1f0f
  practicalswift:
    cr ACK fad1f0f: patch looks correct

Tree-SHA512: 647f9b954fbf52e138d3e710937eb9131b390fef0deae03fd6a162d5a18b9f194010800bbddc8f89208d91be2802dff11c3884d04b3dd233865abd12aa3cde06
@maflcko maflcko deleted the 2004-netNoRecursiveMutex branch January 11, 2021 08:03
@bitcoin bitcoin locked as resolved and limited conversation to collaborators Aug 16, 2022
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