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Don't compact the receive buffer unless we've actually run out of space

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Previously, we would compact the buffer (moving unread data to the
start of the buffer) as follows:

- after processing a message, if there are zero unread bytes, just reset
  the indices for first and last unread byte to zero
- else, if at least 1/8th of the buffer is used, copy remaining data to the beginning of the buffer

The second option is never actually necessary, as before inserting new data
into the array, we already check if there's enough free space, and
compact the buffer first if necessary. So we've been doing a lot of
copies that weren't actually needed. Let's not do that any more.
This commit is contained in:
Jesper Alf Dam
2019-08-07 11:03:12 +02:00
parent e1d50c8c10
commit 7d755d10dc
2 changed files with 37 additions and 19 deletions
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20
core/websock.js
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@@ -27,7 +27,6 @@ export default class Websock {
this._rQi = 0; // Receive queue index
this._rQlen = 0; // Next write position in the receive queue
this._rQbufferSize = 1024 * 1024 * 4; // Receive queue buffer size (4 MiB)
this._rQmax = this._rQbufferSize / 8;
// called in init: this._rQ = new Uint8Array(this._rQbufferSize);
this._rQ = null; // Receive queue
@@ -226,15 +225,15 @@ export default class Websock {
}
_expand_compact_rQ(min_fit) {
const resizeNeeded = min_fit || this.rQlen > this._rQbufferSize / 2;
// if we're using less than 1/8th of the buffer even with the incoming bytes, compact in place
// instead of resizing
const required_buffer_size = (this._rQlen - this._rQi + min_fit) * 8;
const resizeNeeded = this._rQbufferSize < required_buffer_size;
if (resizeNeeded) {
if (!min_fit) {
// just double the size if we need to do compaction
this._rQbufferSize *= 2;
} else {
// otherwise, make sure we satisy rQlen - rQi + min_fit < rQbufferSize / 8
this._rQbufferSize = (this.rQlen + min_fit) * 8;
}
// Make sure we always *at least* double the buffer size, and have at least space for 8x
// the current amount of data
this._rQbufferSize = Math.max(this._rQbufferSize * 2, required_buffer_size);
}
// we don't want to grow unboundedly
@@ -247,7 +246,6 @@ export default class Websock {
if (resizeNeeded) {
const old_rQbuffer = this._rQ.buffer;
this._rQmax = this._rQbufferSize / 8;
this._rQ = new Uint8Array(this._rQbufferSize);
this._rQ.set(new Uint8Array(old_rQbuffer, this._rQi));
} else {
@@ -280,8 +278,6 @@ export default class Websock {
if (this._rQlen == this._rQi) {
this._rQlen = 0;
this._rQi = 0;
} else if (this._rQlen > this._rQmax) {
this._expand_compact_rQ();
}
} else {
Log.Debug("Ignoring empty message");