diff --git a/.idea/.gitignore b/.idea/.gitignore
new file mode 100644
index 0000000..ab1f416
--- /dev/null
+++ b/.idea/.gitignore
@@ -0,0 +1,10 @@
+# Default ignored files
+/shelf/
+/workspace.xml
+# Ignored default folder with query files
+/queries/
+# Datasource local storage ignored files
+/dataSources/
+/dataSources.local.xml
+# Editor-based HTTP Client requests
+/httpRequests/
diff --git a/.idea/compiler.xml b/.idea/compiler.xml
new file mode 100644
index 0000000..812c3f9
--- /dev/null
+++ b/.idea/compiler.xml
@@ -0,0 +1,13 @@
+
+
+
+
+
+
+
+
+
+
+
+
+
\ No newline at end of file
diff --git a/.idea/encodings.xml b/.idea/encodings.xml
new file mode 100644
index 0000000..aa00ffa
--- /dev/null
+++ b/.idea/encodings.xml
@@ -0,0 +1,7 @@
+
+
+
+
+
+
+
\ No newline at end of file
diff --git a/.idea/jarRepositories.xml b/.idea/jarRepositories.xml
new file mode 100644
index 0000000..f4fe6ed
--- /dev/null
+++ b/.idea/jarRepositories.xml
@@ -0,0 +1,20 @@
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
\ No newline at end of file
diff --git a/.idea/misc.xml b/.idea/misc.xml
new file mode 100644
index 0000000..eba6e1f
--- /dev/null
+++ b/.idea/misc.xml
@@ -0,0 +1,12 @@
+
+
+
+
+
+
+
+
\ No newline at end of file
diff --git a/.idea/vcs.xml b/.idea/vcs.xml
new file mode 100644
index 0000000..8306744
--- /dev/null
+++ b/.idea/vcs.xml
@@ -0,0 +1,7 @@
+
+
+
+
+
+
+
\ No newline at end of file
diff --git a/pom.xml b/pom.xml
index 33ea6f3..a768988 100644
--- a/pom.xml
+++ b/pom.xml
@@ -21,6 +21,14 @@
5.12.2
test
+
+
+ org.junit.platform
+ junit-platform-launcher
+ 1.12.2
+ test
+
+
diff --git a/src/main/java/dev/banking/model/BankAccount.java b/src/main/java/dev/banking/model/BankAccount.java
index 745ede2..8277fa6 100644
--- a/src/main/java/dev/banking/model/BankAccount.java
+++ b/src/main/java/dev/banking/model/BankAccount.java
@@ -1,18 +1,15 @@
package dev.banking.model;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
+
public class BankAccount {
private final int accountId;
private long balance;
-
- /*
- * Students may introduce additional fields
- * such as:
- * - Lock / ReentrantLock
- * - ReadWriteLock
- * - Object monitor
- * - etc.
- */
+ private final ReentrantReadWriteLock rwLock = new ReentrantReadWriteLock();
+ private final Lock readLock = rwLock.readLock();
+ private final Lock writeLock = rwLock.writeLock();
public BankAccount(int accountId, long initialBalance) {
this.accountId = accountId;
@@ -23,56 +20,71 @@ public class BankAccount {
return accountId;
}
- /*
- * TODO:
- * Return the current balance in a thread-safe way.
- *
- * Requirements:
- * - Must be safe under concurrent reads/writes
- * - Should not block unnecessarily if using read/write locks
- */
public long getBalance() {
- throw new UnsupportedOperationException("TODO: implement thread-safe balance read");
+ readLock.lock();
+ try
+ {
+ return balance;
+ } finally
+ {
+ readLock.unlock();
+ }
}
- /*
- * TODO:
- * Increase balance atomically.
- *
- * Requirements:
- * - Must not lose updates under concurrency
- */
public void deposit(long amount) {
- throw new UnsupportedOperationException("TODO: implement thread-safe deposit");
+ writeLock.lock();
+ try
+ {
+ balance += amount;
+ } finally
+ {
+ writeLock.unlock();
+ }
}
- /*
- * TODO:
- * Decrease balance atomically.
- *
- * Requirements:
- * - Must not cause race conditions
- * - Negative balance handling is NOT required unless you decide
- * to extend the system (optional)
- */
public void withdraw(long amount) {
- throw new UnsupportedOperationException("TODO: implement thread-safe withdraw");
+ writeLock.lock();
+ try
+ {
+ balance -= amount;
+ } finally
+ {
+ writeLock.unlock();
+ }
}
- /*
- * TODO:
- * Transfer money between two accounts atomically.
- *
- * IMPORTANT REQUIREMENTS:
- * - Must be atomic (no partial transfer)
- * - Must be deadlock-free
- * - Must protect both source and target accounts
- *
- * HINT:
- * - Consider global lock ordering using accountId
- * - Or tryLock with retry strategy
- */
public void transfer(BankAccount target, long amount) {
- throw new UnsupportedOperationException("TODO: implement atomic deadlock-free transfer");
+ if (target == this)
+ {
+ return;
+ }
+ BankAccount first = this;
+ BankAccount second = target;
+
+ if (this.getAccountId() > target.getAccountId())
+ {
+ first = target;
+ second = this;
+ }
+
+
+ first.writeLock.lock();
+ try
+ {
+ second.writeLock.lock();
+ try
+ {
+ //"first" and "second":only for the order of locking to prevent deadlock (have nothing to do with the direction of the transfer)
+ this.balance -= amount;
+ target.balance += amount;
+ } finally
+ {
+ second.writeLock.unlock();
+ }
+ } finally
+ {
+ first.writeLock.unlock();
+ }
}
+
}
\ No newline at end of file