ComputePressure

Chromium only, over HTTPS The Compute Pressure API ships in Chromium-based browsers. Firefox and Safari do not implement it.

Four states, not a number A precise load figure would be a timing side channel, so the API reports a coarse scale: nominal, fair, serious, critical. Treat serious as "shed optional work" - drop a video call's resolution, cut effect quality - and critical as "shed everything you can".

Support and sources

IsSupported / GetKnownSources

GetKnownSources lists what this browser can observe - ['cpu'] today. Worth reading before hard-coding a source, since observing an unknown one simply fails.

@inject Bit.Butil.ComputePressure computePressure

var supported = await computePressure.IsSupported();
var sources = await computePressure.GetKnownSources();

Live sample

support output

Results will appear here when you interact with the samples.

Observe pressure

Observe

The callback fires when the state changes, not on a timer, so a machine sitting at 'nominal' costs nothing. Press the load button below to push this machine up the scale and watch the state follow.

await using var observer = await computePressure.Observe(records =>
{
    foreach (var record in records)
    {
        // record.Source, record.State, record.Time
    }
}, source: "cpu", sampleIntervalMs: 1000);

Live sample

Source

Sample interval (ms, 0 = browser's choice)

pressure output

Results will appear here when you interact with the samples.

API reference

Member

Signature

Description

IsSupported

ValueTask<bool> IsSupported()

True when the runtime exposes PressureObserver. Returns default (false) during prerender/SSR instead of throwing.

GetKnownSources

ValueTask<string[]> GetKnownSources()

The pressure sources this browser can observe - ['cpu'] today.

Observe

ValueTask<ButilSubscription> Observe(Action<PressureRecord[]> handler, string source = 'cpu', int sampleIntervalMs = 0)

Starts observing a source. Dispose the subscription to stop.

DisposeAsync

ValueTask DisposeAsync()

Disconnects every observer this instance started and releases the JS callback reference.

InvokePressureRecords

void InvokePressureRecords(Guid id, PressureRecord[] records)

JSInvokable interop plumbing for pressure records - not intended for app code.

PressureRecord

class PressureRecord { string Source; string State; double Time; }

One sample: the source, one of nominal/fair/serious/critical, and the time on the performance.now() clock.