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Safer Atomic assignment on ARM #302

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merged 2 commits into from
Aug 20, 2024
Merged

Safer Atomic assignment on ARM #302

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On ARM processors, use a safer Atomic assignment to avoid memory reor…
kriszyp Aug 20, 2024
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kriszyp Aug 20, 2024
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2 changes: 1 addition & 1 deletion package.json
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Original file line number Diff line number Diff line change
@@ -1,7 +1,7 @@
{
"name": "lmdb",
"author": "Kris Zyp",
"version": "3.0.13",
"version": "3.0.14",
"description": "Simple, efficient, scalable, high-performance LMDB interface",
"license": "MIT",
"repository": {
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18 changes: 13 additions & 5 deletions write.js
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Expand Up @@ -29,6 +29,7 @@ SYNC_PROMISE_SUCCESS.result = true;
SYNC_PROMISE_FAIL.isSync = true;
SYNC_PROMISE_FAIL.result = false;
const PROMISE_SUCCESS = Promise.resolve(true);
const arch = process.arch;
export const ABORT = 4.452694326329068e-106; // random/unguessable numbers, which work across module/versions and native
export const IF_EXISTS = 3.542694326329068e-103;
const CALLBACK_THREW = {};
Expand Down Expand Up @@ -355,12 +356,19 @@ export function addWriteMethods(

return (callback) => {
if (writtenBatchDepth) {
// if we are in a batch, the transaction can't close, so we do the faster,
// If we are in a batch, the transaction can't close, so we do the faster,
// but non-deterministic updates, knowing that the write thread can
// just poll for the status change if we miss a status update
writeStatus = uint32[flagPosition];
uint32[flagPosition] = flags;
//writeStatus = Atomics.or(uint32, flagPosition, flags)
// just poll for the status change if we miss a status update.
// That is, if we are on x64 architecture...
if (arch === 'x64') {
writeStatus = uint32[flagPosition];
uint32[flagPosition] = flags;
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To be consistent with Atomics.or this should be a |=, but if uint32 is made up of only 0 s then it makes no difference.

} else {
// However, on ARM processors, apparently more radical memory reordering can occur
// so we need to use the slower atomic operation to ensure that a memory barrier is set
// and that the value pointer is actually written before the flag is updated
writeStatus = Atomics.or(uint32, flagPosition, flags);
}
if (writeBatchStart && !writeStatus) {
outstandingBatchCount += 1 + (valueSize >> 12);
if (outstandingBatchCount > batchStartThreshold) {
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