How did the threads understand whether they needed to send a request or not (shared Circuit Breaker counter in a multithreaded environment)?

In a multithreaded environment, the shared Circuit Breaker counter is usually implemented using atomic operations and synchronization so that threads can correctly see and modify the counter's state.

Main approaches:

• Atomic variables (e.g., AtomicInteger in Java) allow safely incrementing or decrementing the counter without locks.
• Volatile variables ensure visibility of changes across threads.
• Locks or synchronized methods provide exclusive access when updating the counter.

Thus, each thread checks the Circuit Breaker state by reading the atomic counter before sending a request. If the counter exceeds the error threshold, requests are blocked. On successful responses, the counter is reset or decreased.

Example in Java using AtomicInteger:

AtomicInteger failureCount = new AtomicInteger(0);
int failureThreshold = 5;

public boolean canSendRequest() {
    return failureCount.get() < failureThreshold;
}

public void onFailure() {
    failureCount.incrementAndGet();
}

public void onSuccess() {
    failureCount.set(0);
}

This way, threads synchronize access to the counter without explicit locks, ensuring correct Circuit Breaker behavior.