diff --git a/.DS_Store b/.DS_Store
new file mode 100644
index 0000000..2c3cd83
Binary files /dev/null and b/.DS_Store differ
diff --git a/.idea/.gitignore b/.idea/.gitignore
new file mode 100644
index 0000000..30cf57e
--- /dev/null
+++ b/.idea/.gitignore
@@ -0,0 +1,10 @@
+# Default ignored files
+/shelf/
+/workspace.xml
+# Editor-based HTTP Client requests
+/httpRequests/
+# Ignored default folder with query files
+/queries/
+# Datasource local storage ignored files
+/dataSources/
+/dataSources.local.xml
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..712ab9d
--- /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..f88c0a7
--- /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/Theoretical Questions.pdf b/Theoretical Questions.pdf
new file mode 100644
index 0000000..dc09a9c
Binary files /dev/null and b/Theoretical Questions.pdf differ
diff --git a/src/.DS_Store b/src/.DS_Store
new file mode 100644
index 0000000..5a8ec8c
Binary files /dev/null and b/src/.DS_Store differ
diff --git a/src/main/java/dev/banking/model/BankAccount.java b/src/main/java/dev/banking/model/BankAccount.java
index 745ede2..721da84 100644
--- a/src/main/java/dev/banking/model/BankAccount.java
+++ b/src/main/java/dev/banking/model/BankAccount.java
@@ -1,18 +1,12 @@
package dev.banking.model;
+import java.util.concurrent.locks.ReentrantLock;
+
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 ReentrantLock lock = new ReentrantLock();
public BankAccount(int accountId, long initialBalance) {
this.accountId = accountId;
@@ -23,56 +17,53 @@ 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");
+ lock.lock();
+ try {
+ return balance;
+ } finally {
+ lock.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");
+ lock.lock();
+ try {
+ balance += amount;
+ } finally {
+ lock.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");
+ lock.lock();
+ try {
+ balance -= amount;
+ } finally {
+ lock.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
+ * Lock ordering by accountId prevents deadlock:
+ * both A->B and B->A transfers always acquire the
+ * lower-id lock first, so no circular wait can form.
*/
public void transfer(BankAccount target, long amount) {
- throw new UnsupportedOperationException("TODO: implement atomic deadlock-free transfer");
+ BankAccount first = this.accountId < target.accountId ? this : target;
+ BankAccount second = this.accountId < target.accountId ? target : this;
+
+ first.lock.lock();
+ try {
+ second.lock.lock();
+ try {
+ this.balance -= amount;
+ target.balance += amount;
+ } finally {
+ second.lock.unlock();
+ }
+ } finally {
+ first.lock.unlock();
+ }
}
-}
\ No newline at end of file
+}