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src: handling v8 thread pool of zero #42524

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src: handling v8 thread pool of zero #42524

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src: handling v8 thread pool of zero
daeyeon Mar 30, 2022
182a83f
doc: fix lint-md ci error
daeyeon Mar 30, 2022
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7 changes: 2 additions & 5 deletions doc/api/cli.md
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Expand Up @@ -1368,11 +1368,8 @@ added: v5.10.0

Set V8's thread pool size which will be used to allocate background jobs.

If set to `0` then V8 will choose an appropriate size of the thread pool based
on the number of online processors.

If the value provided is larger than V8's maximum, then the largest value
will be chosen.
If set to `0` then Node.js will choose an appropriate size of the thread pool
based on the number of online processors.

### `--zero-fill-buffers`

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15 changes: 15 additions & 0 deletions src/node_platform.cc
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Expand Up @@ -45,6 +45,19 @@ static void PlatformWorkerThread(void* data) {
}
}

static int GetActualThreadPoolSize(int thread_pool_size) {
if (thread_pool_size < 1) {
uv_cpu_info_t* cpu_info;
int count;

if (uv_cpu_info(&cpu_info, &count) == 0) {
uv_free_cpu_info(cpu_info, count);
thread_pool_size = count - 1;
}
}
Comment on lines +53 to +57
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I suggest waiting for the upgrade to libuv 1.44 and replacing this with uv_available_parallelism(), it's specifically for use cases such as this one.

uv_cpu_info() isn't really appropriate because it doesn't know how many processors are available to the process, only how many are online.

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uv_available_parallelism() looks more suited to this case indeed. I'll wait for the upgrade to land.

return std::max(thread_pool_size, 1);
}

} // namespace

class WorkerThreadsTaskRunner::DelayedTaskScheduler {
Expand Down Expand Up @@ -340,6 +353,8 @@ NodePlatform::NodePlatform(int thread_pool_size,
// current v8::Platform instance.
SetTracingController(tracing_controller_);
DCHECK_EQ(GetTracingController(), tracing_controller_);

thread_pool_size = GetActualThreadPoolSize(thread_pool_size);
worker_thread_task_runner_ =
std::make_shared<WorkerThreadsTaskRunner>(thread_pool_size);
}
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15 changes: 15 additions & 0 deletions test/parallel/test-worker-v8-pool-size-0.js
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@@ -0,0 +1,15 @@
// Flags: --v8-pool-size=0
'use strict';

const common = require('../common');
const assert = require('assert');
const { Worker, isMainThread } = require('worker_threads');

if (isMainThread) {
const w = new Worker(__filename);
w.on('online', common.mustCall());
w.on('exit', common.mustCall((code) => assert.strictEqual(code, 0)));
process.on('exit', (code) => {
assert.strictEqual(code, 0);
});
}