CheerpX.Linux event callbacks

Event Callbacks for CPU and Disk Monitoring

The CheerpX.Linux instance returned by create provides methods to register and unregister callbacks to monitor CPU and disk activity, as well as disk latency.

registerCallback

registerCallback(eventName: string, callback: (state: string | number) => void): void

Registers a callback function for a specific event type.

Parameters:

• eventName: A string specifying the event type. Can be "cpuActivity", "diskActivity", or "diskLatency".
• callback: A function that will be called when the event occurs. It receives a parameter which varies based on the event type:
  • For "cpuActivity" and "diskActivity": state can be either “ready” (idle, no activity at this time) or “wait” (active, currently in use).
  • For "diskLatency": state is a number representing the time in milliseconds between requesting and receiving the last disk block from the backend.

unregisterCallback

unregisterCallback(eventName: string, callback: (state: string | number) => void): void

Unregisters a previously registered callback function for a specific event type.

Parameters:

• eventName: A string specifying the event type. See the registerCallback reference above for the supported event types.
• callback: The function to be unregistered.

Example usage:

function hddCallback(state) {
  if (state === "ready") {
    console.log("Disk Activity: Ready");
  } else {
    console.log("Disk Activity: Busy");
  }
}

function cpuCallback(state) {
  if (state === "ready") {
    console.log("CPU Status: Ready");
  } else {
    console.log("CPU Status: Busy");
  }
}

function latencyCallback(latency) {
  console.log(`Last Disk Latency: ${latency} ms`);
}

if (cx) {
  cx.registerCallback("cpuActivity", cpuCallback);
  cx.registerCallback("diskActivity", hddCallback);
  cx.registerCallback("diskLatency", latencyCallback);

  // Simulate CPU, disk activity, and latency logs for testing purposes
  setInterval(() => {
    // Simulate CPU activity
    const state = Math.random() > 0.5 ? "ready" : "busy";
    cpuCallback(state);

    // Simulate disk activity
    const diskState = Math.random() > 0.5 ? "ready" : "busy";
    hddCallback(diskState);

    // Random latency between 0 and 99 ms
    const simulatedLatency = Math.floor(Math.random() * 100);
    latencyCallback(simulatedLatency);
  }, 3000);
}

// Later, if needed:
// cx.unregisterCallback("cpuActivity", cpuCallback);
// cx.unregisterCallback("diskActivity", hddCallback);
// cx.unregisterCallback("diskLatency", latencyCallback);

This example demonstrates how to register callbacks for CPU activity, disk activity, and disk latency. The CPU and disk activity callbacks log the current state (either “ready” or “busy”) to the console, while the disk latency callback logs the latency of the last downloaded disk block. Additionally, the simulated events are generated for testing purposes, allowing you to see output for all three types of activity.

processCreated Event

The processCreated event is triggered by the CheerpX engine whenever a native process is created. This includes actions such as running a command within the WebVM terminal. The event provides a mechanism to track the number of processes created during the session.

How it works

Here’s how the processCreated event is utilized in the code:

1. Callback Registration:

During the initialization of the CheerpX environment, the event is registered with the callback handleProcessCreated.

cx.registerCallback("processCreated", handleProcessCreated);

2. Callback implementation

function handleProcessCreated() {
  processCount++;
  console.log(`Process count: ${processCount}`);
}

The handleProcessCreated function will now increment the processCount variable each time it’s called.