src/main/java/com/it_jaros/networkScanner/FdCounter.java


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package com.it_jaros.networkScanner;

import java.lang.management.ManagementFactory;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;

import com.sun.management.UnixOperatingSystemMXBean;

public final class FdCounter implements AutoCloseable {
    private final UnixOperatingSystemMXBean os =
            (UnixOperatingSystemMXBean) ManagementFactory.getOperatingSystemMXBean();
    private final ScheduledExecutorService ses =
            Executors.newSingleThreadScheduledExecutor(Thread.ofPlatform().daemon().factory());
    private final AtomicLong peak = new AtomicLong(0);
    private long baseline;

    public void start(long everyMillis) {
        this.baseline = os.getOpenFileDescriptorCount();
        ses.scheduleAtFixedRate(() -> {
            long now = os.getOpenFileDescriptorCount();
            peak.accumulateAndGet(now, Math::max);
        }, 0, everyMillis, TimeUnit.MILLISECONDS);
    }

    public long peakOpenFds() {
        return peak.get();
    }

    public long maxFds() {
        return os.getMaxFileDescriptorCount();
    }
    
    public long baseline() {
        return this.baseline;
    }

    @Override public void close() {
        ses.shutdownNow();
    }
}