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Remove use of removeAll(keepingCapacity:). (#1699) 

Motivation:

As outlined in https://bugs.swift.org/browse/SR-13923,
removeAll(keepingCapacity:) on Array has particularly negative
performance when that Array is not uniquely referenced. In this case, in
EmbeddedChannel, we _arrange_ to multiply reference it. This makes it
swamp our HTTP/2 microbenchmarks, spending more cycles copying this
buffer around than doing anything else.

Modifications:

- Just allocate a new buffer instead.

Result:

Much less copying.
This commit is contained in:
Cory Benfield 2020-12-01 08:08:06 +00:00 committed by GitHub
parent 8b47ef29a8
commit 2bae395344
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1 changed files with 4 additions and 1 deletions
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Sources/NIO/Embedded.swift
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@ -281,7 +281,10 @@ class EmbeddedChannelCore: ChannelCore {
func flush0() {
let pendings = self.pendingOutboundBuffer
self.pendingOutboundBuffer.removeAll(keepingCapacity: true)
// removeAll(keepingCapacity:) is strictly more expensive than doing this, see
// https://bugs.swift.org/browse/SR-13923.
self.pendingOutboundBuffer = []
self.pendingOutboundBuffer.reserveCapacity(pendings.capacity)
for dataAndPromise in pendings {
self.addToBuffer(buffer: &self.outboundBuffer, data: dataAndPromise.0)
dataAndPromise.1?.succeed(())