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LogClient.java
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LogClient.java
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package logger;
import java.util.*;
import java.util.concurrent.*;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
public interface LogClient {
/**
* When a process starts, it calls 'start' with processId.
*/
void start(String processId, long timestamp);
/**
* When the same process ends, it calls 'end' with processId.
*/
void end(String processId);
/**
* Polls the first log entry of a completed process sorted by the start time of processes in the below format
* {processId} started at {startTime} and ended at {endTime}
* <p>
* process id = 1 --> 12, 15
* process id = 2 --> 8, 12
* process id = 3 --> 7, 19
* <p>
* {3} started at {7} and ended at {19}
* {2} started at {8} and ended at {12}
* {1} started at {12} and ended at {15}
*/
String poll();
}
class LoggerImplementation implements LogClient {
private final Map<String, Process> processes;
private final ConcurrentSkipListMap<Long, Process> queue;
private final List<CompletableFuture<Void>> futures;
private final Lock lock;
private final ExecutorService[] taskScheduler;
public LoggerImplementation() {
this.processes = new ConcurrentHashMap<>();
this.queue = new ConcurrentSkipListMap<>();
this.futures = new CopyOnWriteArrayList<>();
this.lock = new ReentrantLock();
this.taskScheduler = new ExecutorService[10];
for (int i = 0; i < taskScheduler.length; i++) {
taskScheduler[i] = Executors.newSingleThreadExecutor();
}
}
@Override
public void start(String processId, long timestamp) { //1
taskScheduler[processId.hashCode() % taskScheduler.length].execute(() -> {
final Process process = new Process(processId, timestamp);
processes.put(processId, process);
queue.put(timestamp, process);
});
}
@Override
public void end(String processId) { //1
taskScheduler[processId.hashCode() % taskScheduler.length].execute(() -> {
lock.lock();//1
try {
final long now = System.currentTimeMillis();//1
processes.get(processId).setEndTime(now);//1
if (!futures.isEmpty() && queue.firstEntry().getValue().getId().equals(processId)) {
pollNow();
final var result = futures.remove(0);
result.complete(null);
}
} finally {
lock.unlock();
}
});
}
@Override
public String poll() {
lock.lock();
try {
final var result = new CompletableFuture<Void>();
if (!queue.isEmpty() && queue.firstEntry().getValue().getEndTime() != -1) {
pollNow();
} else {
futures.add(result);
}
try {
result.get(3, TimeUnit.SECONDS);
} catch (InterruptedException | ExecutionException | TimeoutException e) {
throw new RuntimeException(e);
}
return null;
} finally {
lock.unlock();
}
}
private String pollNow() {
final Process process = queue.firstEntry().getValue();
final var logStatement = process.getId() + " started at " + process.getStartTime() + " and ended at " + process.getEndTime();
System.out.println(logStatement);
processes.remove(process.getId());
queue.pollFirstEntry();
return logStatement;
}
}
class Process {
private final String id;
private final long startTime;
private long endTime;
public Process(final String id, final long startTime) {
this.id = id;
this.startTime = startTime;
endTime = -1;
}
public String getId() {
return id;
}
public long getStartTime() {
return startTime;
}
public long getEndTime() {
return endTime;
}
public void setEndTime(long endTime) {
this.endTime = endTime;
}
}
class LoggerMain {
/*
* {3} started at {7} and ended at {19}
* {2} started at {8} and ended at {12}
* {1} started at {12} and ended at {15}
*/
public static void main(String[] args) {
final LogClient logger = new LoggerImplementation();
logger.start("1", 1);
logger.poll();
logger.start("3", 2);
logger.poll();
logger.end("1");
logger.poll();
logger.start("2", 3);
logger.poll();
logger.end("2");
logger.poll();
logger.end("3");
logger.poll();
logger.poll();
logger.poll();
//1
//3
//2
}
}