- * 1. When it contains the reference of {@link readerLock}, it means that the lock is acquired by
- * the reader, another reader can also do the read operation concurrently.
- * 2. When it contains the reference of reference of {@link writerLock}, it means that the lock is
- * acquired by the writer exclusively, no more reader or writer can get the lock.
+ * 1. When it contains the reference of {@link readerLock}, it means that the lock is acquired by the reader, another
+ * reader can also do the read operation concurrently.
+ * 2. When it contains the reference of reference of {@link writerLock}, it means that the lock is acquired by the
+ * writer exclusively, no more reader or writer can get the lock.
*
* This is the most important field in this class to control the access for reader/writer.
*/
@@ -74,13 +79,6 @@ public class ReaderWriterLock implements ReadWriteLock {
return globalMutex.contains(writerLock);
}
- /**
- * return true when globalMutex hold the reference of readerLock
- */
- private boolean doesReaderOwnThisLock() {
- return globalMutex.contains(readerLock);
- }
-
/**
* Nobody get the lock when globalMutex contains nothing
*
@@ -89,14 +87,6 @@ public class ReaderWriterLock implements ReadWriteLock {
return globalMutex.isEmpty();
}
- private static void waitUninterruptibly(Object o) {
- try {
- o.wait();
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- }
-
/**
* Reader Lock, can be access for more than one reader concurrently if no writer get the lock
*/
@@ -104,31 +94,35 @@ public class ReaderWriterLock implements ReadWriteLock {
@Override
public void lock() {
-
synchronized (readerMutex) {
-
currentReaderCount++;
if (currentReaderCount == 1) {
- // Try to get the globalMutex lock for the first reader
- synchronized (globalMutex) {
- while (true) {
- // If the no one get the lock or the lock is locked by reader, just set the reference
- // to the globalMutex to indicate that the lock is locked by Reader.
- if (isLockFree() || doesReaderOwnThisLock()) {
- globalMutex.add(this);
- break;
- } else {
- // If lock is acquired by the write, let the thread wait until the writer release
- // the lock
- waitUninterruptibly(globalMutex);
- }
- }
- }
-
+ acquireForReaders();
}
}
}
+ /**
+ * Acquire the globalMutex lock on behalf of current and future concurrent readers. Make sure no writers currently
+ * owns the lock.
+ */
+ private void acquireForReaders() {
+ // Try to get the globalMutex lock for the first reader
+ synchronized (globalMutex) {
+ // If the no one get the lock or the lock is locked by reader, just set the reference
+ // to the globalMutex to indicate that the lock is locked by Reader.
+ while (doesWriterOwnThisLock()) {
+ try {
+ globalMutex.wait();
+ } catch (InterruptedException e) {
+ LOGGER.info("InterruptedException while waiting for globalMutex in acquireForReaders", e);
+ Thread.currentThread().interrupt();
+ }
+ }
+ globalMutex.add(this);
+ }
+ }
+
@Override
public void unlock() {
@@ -179,23 +173,17 @@ public class ReaderWriterLock implements ReadWriteLock {
synchronized (globalMutex) {
- while (true) {
- // When there is no one acquired the lock, just put the writeLock reference to the
- // globalMutex to indicate that the lock is acquired by one writer.
- // It is ensure that writer can only get the lock when no reader/writer acquired the lock.
- if (isLockFree()) {
- globalMutex.add(this);
- break;
- } else if (doesWriterOwnThisLock()) {
- // Wait when other writer get the lock
- waitUninterruptibly(globalMutex);
- } else if (doesReaderOwnThisLock()) {
- // Wait when other reader get the lock
- waitUninterruptibly(globalMutex);
- } else {
- throw new AssertionError("it should never reach here");
+ // Wait until the lock is free.
+ while (!isLockFree()) {
+ try {
+ globalMutex.wait();
+ } catch (InterruptedException e) {
+ LOGGER.info("InterruptedException while waiting for globalMutex to begin writing", e);
+ Thread.currentThread().interrupt();
}
}
+ // When the lock is free, acquire it by placing an entry in globalMutex
+ globalMutex.add(this);
}
}
diff --git a/reader-writer-lock/src/main/java/com/iluwatar/reader/writer/lock/Writer.java b/reader-writer-lock/src/main/java/com/iluwatar/reader/writer/lock/Writer.java
index c468a61f8..dc379eef9 100644
--- a/reader-writer-lock/src/main/java/com/iluwatar/reader/writer/lock/Writer.java
+++ b/reader-writer-lock/src/main/java/com/iluwatar/reader/writer/lock/Writer.java
@@ -22,11 +22,11 @@
*/
package com.iluwatar.reader.writer.lock;
+import java.util.concurrent.locks.Lock;
+
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
-import java.util.concurrent.locks.Lock;
-
/**
* Writer class, write when it acquired the write lock
*/
@@ -37,10 +37,30 @@ public class Writer implements Runnable {
private Lock writeLock;
private String name;
+
+ private long writingTime;
+ /**
+ * Create new Writer who writes for 250ms
+ *
+ * @param name - Name of the thread owning the writer
+ * @param writeLock - Lock for this writer
+ */
public Writer(String name, Lock writeLock) {
+ this(name, writeLock, 250L);
+ }
+
+ /**
+ * Create new Writer
+ *
+ * @param name - Name of the thread owning the writer
+ * @param writeLock - Lock for this writer
+ * @param writingTime - amount of time (in milliseconds) for this reader to engage writing
+ */
+ public Writer(String name, Lock writeLock, long writingTime) {
this.name = name;
this.writeLock = writeLock;
+ this.writingTime = writingTime;
}
@@ -50,18 +70,19 @@ public class Writer implements Runnable {
try {
write();
} catch (InterruptedException e) {
- e.printStackTrace();
+ LOGGER.info("InterruptedException when writing", e);
+ Thread.currentThread().interrupt();
} finally {
writeLock.unlock();
}
}
-
+
/**
* Simulate the write operation
*/
public void write() throws InterruptedException {
LOGGER.info("{} begin", name);
- Thread.sleep(250);
- LOGGER.info("{} finish", name);
+ Thread.sleep(writingTime);
+ LOGGER.info("{} finished after writing {}ms", name, writingTime);
}
}
diff --git a/reader-writer-lock/src/test/java/com/iluwatar/reader/writer/lock/utils/InMemoryAppender.java b/reader-writer-lock/src/test/java/com/iluwatar/reader/writer/lock/utils/InMemoryAppender.java
index 30624a650..b8ad531ce 100644
--- a/reader-writer-lock/src/test/java/com/iluwatar/reader/writer/lock/utils/InMemoryAppender.java
+++ b/reader-writer-lock/src/test/java/com/iluwatar/reader/writer/lock/utils/InMemoryAppender.java
@@ -52,6 +52,6 @@ public class InMemoryAppender extends AppenderBase