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fs: improve fsPromises readFile performance
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Improve the fsPromises readFile performance
by allocating only one buffer, when size is known,
increase the size of the readbuffer chunks,
and dont read more data if size bytes have been read

Refs: #37583
PR-URL: #37608
Backport-PR-URL: #39838
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
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Linkgoron authored and targos committed Sep 4, 2021
1 parent a4d6f78 commit 2b0e270
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Showing 2 changed files with 44 additions and 16 deletions.
45 changes: 34 additions & 11 deletions lib/internal/fs/promises.js
Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,7 @@
const kWriteFileMaxChunkSize = 2 ** 14;

const {
ArrayPrototypePush,
Error,
MathMax,
MathMin,
Expand Down Expand Up @@ -293,24 +294,46 @@ async function readFileHandle(filehandle, options) {
if (size > kIoMaxLength)
throw new ERR_FS_FILE_TOO_LARGE(size);

const chunks = [];
const chunkSize = size === 0 ?
kReadFileMaxChunkSize :
MathMin(size, kReadFileMaxChunkSize);
let endOfFile = false;
let totalRead = 0;
const noSize = size === 0;
const buffers = [];
const fullBuffer = noSize ? undefined : Buffer.allocUnsafeSlow(size);
do {
if (signal && signal.aborted) {
throw lazyDOMException('The operation was aborted', 'AbortError');
}
const buf = Buffer.alloc(chunkSize);
const { bytesRead, buffer } =
await read(filehandle, buf, 0, chunkSize, -1);
endOfFile = bytesRead === 0;
if (bytesRead > 0)
chunks.push(buffer.slice(0, bytesRead));
let buffer;
let offset;
let length;
if (noSize) {
buffer = Buffer.allocUnsafeSlow(kReadFileUnknownBufferLength);
offset = 0;
length = kReadFileUnknownBufferLength;
} else {
buffer = fullBuffer;
offset = totalRead;
length = MathMin(size - totalRead, kReadFileBufferLength);
}

const bytesRead = (await binding.read(filehandle.fd, buffer, offset,
length, -1, kUsePromises)) || 0;
totalRead += bytesRead;
endOfFile = bytesRead === 0 || totalRead === size;
if (noSize && bytesRead > 0) {
const isBufferFull = bytesRead === kReadFileUnknownBufferLength;
const chunkBuffer = isBufferFull ? buffer : buffer.slice(0, bytesRead);
ArrayPrototypePush(buffers, chunkBuffer);
}
} while (!endOfFile);

const result = chunks.length === 1 ? chunks[0] : Buffer.concat(chunks);
let result;
if (size > 0) {
result = totalRead === size ? fullBuffer : fullBuffer.slice(0, totalRead);
} else {
result = buffers.length === 1 ? buffers[0] : Buffer.concat(buffers,
totalRead);
}

return options.encoding ? result.toString(options.encoding) : result;
}
Expand Down
15 changes: 10 additions & 5 deletions test/parallel/test-fs-promises-file-handle-readFile.js
Original file line number Diff line number Diff line change
Expand Up @@ -11,7 +11,7 @@ const {
open,
readFile,
writeFile,
truncate
truncate,
} = fs.promises;
const path = require('path');
const tmpdir = require('../common/tmpdir');
Expand Down Expand Up @@ -65,6 +65,7 @@ async function doReadAndCancel() {
await assert.rejects(readFile(fileHandle, { signal }), {
name: 'AbortError'
});
await fileHandle.close();
}

// Signal aborted on first tick
Expand All @@ -75,10 +76,11 @@ async function doReadAndCancel() {
fs.writeFileSync(filePathForHandle, buffer);
const controller = new AbortController();
const { signal } = controller;
tick(1, () => controller.abort());
process.nextTick(() => controller.abort());
await assert.rejects(readFile(fileHandle, { signal }), {
name: 'AbortError'
});
}, 'tick-0');
await fileHandle.close();
}

// Signal aborted right before buffer read
Expand All @@ -91,10 +93,12 @@ async function doReadAndCancel() {

const controller = new AbortController();
const { signal } = controller;
tick(2, () => controller.abort());
tick(1, () => controller.abort());
await assert.rejects(fileHandle.readFile({ signal, encoding: 'utf8' }), {
name: 'AbortError'
});
}, 'tick-1');

await fileHandle.close();
}

// Validate file size is within range for reading
Expand All @@ -112,6 +116,7 @@ async function doReadAndCancel() {
name: 'RangeError',
code: 'ERR_FS_FILE_TOO_LARGE'
});
await fileHandle.close();
}
}

Expand Down

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