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This noncompliant code example protects a resource, an open file, by using a ReentrantLock but . However, the method fails to release the lock when an exception occurs while performing operations on the open file. When an exception is thrown, control transfers to the catch block and the call to unlock() fails to execute never executes.
| Code Block |
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public final class Client {
public void doSomething(File file) {
final Lock lock = new ReentrantLock();
InputStream in = null;
try {
lock.lock();
in = new FileInputStream(file);
// Perform operations on the open file
lock.unlock();
} catch (FileNotFoundException x) {
// Handle exception
} finally {
if (in != null) {
try {
in.close();
} catch (IOException x) {
// Handle exception
}
}
}
}
}
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This compliant solution encapsulates operations that could throw an exception in a try block immediately after acquiring the lock. The lock is acquired just before the try block, which guarantees that it is held when the finally block executes. Invoking Lock.unlock() in the finally block ensures that the lock is released regardless of whether or not an exception occurs or not.
| Code Block |
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public final class Client {
public void doSomething(File file) {
final Lock lock = new ReentrantLock();
InputStream in = null;
lock.lock();
try {
in = new FileInputStream(file);
// Perform operations on the open file
} catch (FileNotFoundException fnf) {
// Forward to handler
} finally {
lock.unlock();
if (in != null) {
try {
in.close();
} catch (IOException e) {
// Forward to handler
}
}
}
}
}
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final class DateHandler {
private final Date date = new Date();
final Lock lock = new ReentrantLock();
// str could be null
public void doSomething(String str) {
lock.lock();
String dateString = date.toString();
if (str.equals(dateString)) {
// ...
}
// ...
lock.unlock();
}
}
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| Code Block |
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final class DateHandler {
private final Date date = new Date();
final Lock lock = new ReentrantLock();
// str could be null
public void doSomething(String str) {
lock.lock();
try {
String dateString = date.toString();
if (str != null && str.equals(dateString)) {
// ...
}
// ...
} finally {
lock.unlock();
}
}
}
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