Tuesday, April 30, 2024

Angular 17 Notes

 ng version 17 requires node 18 or above (20 prefer)

angular cli to generate boilerplate application

npm install -g @angular/cli 17.0.10

ng new csfox --skip-tests --skip-git

Friday, March 1, 2024

Java MemoryMonitor

 To programmatically detect low memory conditions and pause a worker thread in Java 11, you can use the Runtime class to monitor the JVM's memory usage. Here's a step-by-step approach:

  1. Retrieve Memory Usage Metrics: Use the Runtime class to get information about the heap memory usage. The totalMemory() method returns the total memory currently available to the JVM, freeMemory() returns the amount of free memory in the JVM, and maxMemory() returns the maximum amount of memory that the JVM will attempt to use
  2. Calculate Memory Usage: To determine the used memory, subtract freeMemory() from totalMemory(). To check if the memory is running low, compare the used memory with maxMemory() to see how close you are to the limit
  3. Implement a Memory Check: Create a method that checks memory usage and returns a boolean indicating whether memory is low. You might define "low memory" as when the used memory exceeds a certain percentage of the maximum memory.
  4. Pause Worker Thread: In your worker thread, periodically call the memory check method. If it returns true, indicating low memory, you can pause the thread using Thread.sleep() to wait for memory to be freed up, possibly by the garbage collector or completion of other tasks
Here's a simple example of how you might implement this:
public class MemoryManager { public static boolean isMemoryLow() { Runtime runtime = Runtime.getRuntime(); long usedMemory = runtime.totalMemory() - runtime.freeMemory(); long maxMemory = runtime.maxMemory(); double usedPercentage = (double) usedMemory / maxMemory; // Define a threshold, e.g., 90% of max memory usage return usedPercentage > 0.9; } public static void main(String[] args) { Thread workerThread = new Thread(() -> { try { while (true) { // Perform work here // Check memory status if (isMemoryLow()) { // Pause if memory is low System.out.println("Memory is low, pausing..."); Thread.sleep(10000); // Pause for 10 seconds } } } catch (InterruptedException e) { Thread.currentThread().interrupt(); } }); workerThread.start(); } }
In this example, the isMemoryLow() method checks if the used memory exceeds 90% of the maximum memory. The worker thread periodically checks the memory status and pauses if necessary.Remember that calling System.gc() to force garbage collection is generally discouraged because it can lead to performance issues, and the JVM is usually better at managing garbage collection on its own
 Instead, rely on the garbage collector to run as needed, and design your application to handle low memory conditions gracefully.


how to pause a worker thread in java
how to monitor memory usage in java
how to set up an alert for low memory in java

  1. Use MemoryMXBean: Utilize the MemoryMXBean class from the java.lang.management package to monitor memory usage.
  2. Get Memory Usage: Retrieve memory usage information using MemoryMXBean.getHeapMemoryUsage() and MemoryMXBean.getNonHeapMemoryUsage() methods.
  3. Check Memory Threshold: Define a threshold for low memory based on available physical memory or heap usage.
  4. Pause Worker Threads: Implement logic to pause worker threads when memory usage surpasses the threshold.
  5. Resume Threads: Once memory usage decreases below the threshold, resume the paused worker threads.
import java.lang.management.ManagementFactory;
import java.lang.management.MemoryMXBean;
import java.lang.management.MemoryUsage;

public class MemoryMonitor {
    private MemoryMXBean memoryMXBean;

    public MemoryMonitor() {
        memoryMXBean = ManagementFactory.getMemoryMXBean();

    public boolean isMemoryLow() {
        MemoryUsage heapMemoryUsage = memoryMXBean.getHeapMemoryUsage();
        MemoryUsage nonHeapMemoryUsage = memoryMXBean.getNonHeapMemoryUsage();
        // Define your threshold based on available physical memory or heap usage
        long totalMemory = Runtime.getRuntime().totalMemory();
        long maxMemory = Runtime.getRuntime().maxMemory();
        long usedMemory = totalMemory - Runtime.getRuntime().freeMemory();
        long memoryThreshold = maxMemory / 2; // Example threshold
        return usedMemory > memoryThreshold;

    // Implement logic to pause and resume worker threads
    // Pause worker threads when memory is low and resume when memory is back to normal

  1. stackoverflow.com - Java program running out of RAM but not really
  2. docs.oracle.com - 2 Diagnostic Tools - Java
  3. toptal.com - Hunting Java Memory Leaks
  4. dzone.com - Troubleshooting Problems With Native (Off-Heap) Memory
  5. datadoghq.com - Monitor Java memory management with runtime metrics