JVM / Java / Threads / Scheduled Executor
1. ScheduledExecutorService
ScheduledExecutor is a specialized ExecutorService that can: - Run tasks after a delay - Run tasks periodically (fixed rate or fixed delay) Before Java 5, developers used Timer / TimerTask. There was a single thread and one bad task could kill the timer. SchedulerExecutorService fixed all of this. Think of it as an Executor + timer + thread pool.
/**
* =================================
* Trading Background Jobs
* ==================================
* ScheduledExecutorService - Example
*/
package threads.scheduled_executor;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
public class TradingBackgroundJobs {
public static void main(String[] args) throws InterruptedException {
ScheduledExecutorService scheduler =
Executors.newScheduledThreadPool(
2,
new SchedulerThreadFactory()
);
// 1. Market data refresh - fixed rate
scheduler.scheduleAtFixedRate(
new MarketDataRefresher(), // command
0, // initial delay
1, // period
TimeUnit.SECONDS // unit
);
// 2. Risk checks - fixed delay
scheduler.scheduleWithFixedDelay(
new RiskCheckTask(),
0,
5,
TimeUnit.SECONDS
);
// 3. One-time cleanup after delay
scheduler.schedule(
new ExpiredOrderCleanup(),
10,
TimeUnit.SECONDS
);
// Let the system run for a while
Thread.sleep(20_000);
System.out.println("Shutting down scheduler ...");
scheduler.shutdown();
/*
[scheduler-worker-1] Refreshing market price ...
[scheduler-worker-2] Running risk checks ...
[scheduler-worker-1] Refreshing market price ...
[scheduler-worker-1] Refreshing market price ...
[scheduler-worker-2] Risk checks completed
[scheduler-worker-1] Refreshing market price ...
[scheduler-worker-1] Refreshing market price ...
[scheduler-worker-1] Refreshing market price ...
[scheduler-worker-1] Refreshing market price ...
[scheduler-worker-1] Refreshing market price ...
[scheduler-worker-2] Running risk checks ...
[scheduler-worker-1] Refreshing market price ...
[scheduler-worker-1] Refreshing market price ...
[scheduler-worker-2] Risk checks completed
[scheduler-worker-2] Refreshing market price ...
[scheduler-worker-1] Cleaning up expired orders ...
[scheduler-worker-2] Refreshing market price ...
[scheduler-worker-1] Cleanup completed
[scheduler-worker-2] Refreshing market price ...
[scheduler-worker-2] Refreshing market price ...
[scheduler-worker-2] Refreshing market price ...
[scheduler-worker-1] Running risk checks ...
[scheduler-worker-2] Refreshing market price ...
[scheduler-worker-2] Refreshing market price ...
[scheduler-worker-1] Risk checks completed
[scheduler-worker-1] Refreshing market price ...
[scheduler-worker-1] Refreshing market price ...
[scheduler-worker-1] Refreshing market price ...
Shutting down scheduler ...
[scheduler-worker-1] Refreshing market price ...
*/
}
}
class SchedulerThreadFactory implements ThreadFactory {
private final AtomicInteger counter = new AtomicInteger(1);
@Override
public Thread newThread(Runnable r) {
Thread t = new Thread(r);
t.setName("scheduler-worker-" + counter.getAndIncrement());
return t;
}
}
/**
* ===================================
* Market Data - Refresher
* ===================================
* - runs at a fixed rate
* - exception-safe
* - typical low-latency trading task
*/
class MarketDataRefresher implements Runnable {
@Override
public void run() {
try {
System.out.printf(
"[%s] Refreshing market price ... %n",
Thread.currentThread().getName()
);
// Simulate market data fetch
Thread.sleep(300);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
} catch (Exception e) {
// IMPORTANT: never let exceptions escape
System.err.println("Market data refresh failed: " + e.getMessage());
}
}
}
/**
* ============================================
* Risk Check - Task
* ============================================
* - No overlap
* - Each run starts after the previous finishes
* - Perfect for audits and controls
*/
class RiskCheckTask implements Runnable {
@Override
public void run() {
try {
System.out.printf(
"[%s] Running risk checks ... %n",
Thread.currentThread().getName()
);
// Simulate heavy calculations
Thread.sleep(2000);
System.out.printf(
"[%s] Risk checks completed %n",
Thread.currentThread().getName()
);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
} catch (Exception e) {
System.err.println("Risk check failed: " + e.getMessage());
}
}
}
/**
* Expired Order Clean
* ==========================
* - Runs once
* - Delayed startup
* - Typical maintenance job
*/
class ExpiredOrderCleanup implements Runnable {
@Override
public void run() {
try {
System.out.printf(
"[%s] Cleaning up expired orders ... %n",
Thread.currentThread().getName()
);
// Simulate clean up
Thread.sleep(1000);
System.out.printf(
"[%s] Cleanup completed %n",
Thread.currentThread().getName()
);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
} catch (Exception e) {
System.err.println("Expired order cleanup failed: " + e.getMessage());
}
}
}
