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30a4e3b734 | ||
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d1c3e552a0 |
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## start() vs run()
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**Q1**
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**the output:**
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Calling run()
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Running in: main
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Calling start()
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Running in: Thread-2
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**answer to why:** run() is executed by main thread although start() is executed by thread object that been created.
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**Q2**
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the difference between these two, is that when a thread (which has been created as an object) calls run(), couldn't execute it. So the method will be executed by the thread that created t1.
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But by calling start(), you wouldn't see this behavior and method will be executed by thread that been created as t2.
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## Deamon Threads
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**Q1**
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**the output:**
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Main thread ends.
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Daemon thread running...
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**answer to why:** Main thread executes faster than deamon thread and exits the program so it doesn't let deamon thread execute properly.
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**Q2**
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the thread will execute properly and we'll see "Daemon thread running..." prints for 20 times after printing "Main thread ends.".
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**Q3**
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for example one of use cases is Logging and Auditing Services. Daemon threads can be used to log background activities continuously.
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## A shorter way to create threads
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**Q1**
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**the output:** Thread is running using a ...!
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**Q2**
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Java Lambda
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**Q3**
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it is the easiest way to create a thread. All three ways do the same execution. But with different usages.
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@@ -1,5 +1,7 @@
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import java.util.Random;
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import static java.lang.Thread.sleep;
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/**
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* Simulates downloading a single chunk of a file.
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*
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@@ -22,22 +24,38 @@ public class DownloadWorker implements Runnable {
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@Override
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public void run() {
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// TODO: Record the chunk start time in chunkStatus.
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chunkStatus.setStartTimeMs(System.currentTimeMillis());
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double downloaded = 0.0;
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// TODO: Print a message that this chunk has started downloading.
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System.out.println(chunkStatus.getChunkId() + " has started downloading...");
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while (downloaded < chunkStatus.getChunkSizeMB()) {
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// TODO: Generate a random sleep delay between min and max delay.
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int delayTime = random.nextInt(config.getMinStepDelayMs(), config.getMaxStepDelayMs());
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// TODO: Sleep for that delay.
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try {
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Thread.sleep(delayTime);
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} catch (InterruptedException e) {
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throw new RuntimeException(e); // not sure about this one!
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}
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// TODO: Generate a random download amount for this step.
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double currentDownloaded = random.nextDouble(config.getMinStepDownloadMB(), config.getMaxStepDownloadMB());
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// TODO: Increase downloaded, but do not go beyond chunk size.
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while (downloaded <= 120) {
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downloaded += currentDownloaded;
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}
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// TODO: Save the updated downloaded value into chunkStatus.
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chunkStatus.setDownloadedMB(downloaded);
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// TODO: Optionally print step-by-step progress.
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}
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// TODO: Mark the chunk as completed.
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chunkStatus.setCompleted(true);
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// TODO: Record the chunk end time in chunkStatus.
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chunkStatus.setEndTimeMs(System.currentTimeMillis());
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// TODO: Print a message that this chunk has finished downloading.
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System.out.println(chunkStatus.getChunkId() + " has finished downloading.");
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}
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}
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+18
-3
@@ -37,7 +37,9 @@ public class Main {
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// TODO:
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// Students may print helpful debug information here,
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// for example which chunk is assigned to which worker thread.
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System.out.println(chunk.getChunkId() + " is assigned to " + workerThread.getName());
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}
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System.out.println();
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// 4. Create and start monitor thread
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ProgressMonitor monitor = new ProgressMonitor(config, chunks);
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@@ -49,11 +51,15 @@ public class Main {
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//
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// Example idea:
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// monitorThread.start();
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monitorThread.start();
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// 5. Start worker threads
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// TODO:
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// Start each worker thread in workerThreads.
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// Use a loop and call start() on each thread.
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for (Thread wT: workerThreads){
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wT.start();
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}
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// 6. Wait for workers to finish
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// TODO:
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@@ -61,9 +67,13 @@ public class Main {
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// This should be done inside a try-catch block for InterruptedException.
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//
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// Hint:
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// for (Thread thread : workerThreads) {
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// thread.join();
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// }
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for (Thread thread : workerThreads) {
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try {
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thread.join();
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} catch (InterruptedException e) {
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throw new RuntimeException(e);
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}
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}
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// TODO:
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// After all workers finish, the monitor thread may also need to stop.
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@@ -72,6 +82,11 @@ public class Main {
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// - add a stopping mechanism in ProgressMonitor later.
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//
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// If your monitor finishes automatically, you may join it here.
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try {
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monitorThread.join();
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} catch (InterruptedException e) {
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throw new RuntimeException(e);
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}
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// NOTE:
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// this final report may show 0 progress because no worker has actually run yet.
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@@ -57,6 +57,11 @@ public class ProgressMonitor implements Runnable {
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// TODO:
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// If all chunks are completed, print a final message and exit the loop
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if (completedChunks == chunks.size())
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{
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System.out.println("all chunks are completed!");
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break;
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}
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try {
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Thread.sleep(monitorDelayMs);
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