Pattern: Synchronized on ReentrantLock
Issue: -
Synchronizing on a ReentrantLock field is almost never the intended usage. A ReentrantLock should be obtained using the lock() method and released in a finally block using the unlock() method.
Here is the proper usage of ReentrantLock:
import java.util.concurrent.locks.ReentrantLock;
final lock = new ReentrantLock();
def method() {
//Trying to enter the critical section
lock.lock(); // will wait until this thread gets the lock
try {
// critical section
} finally {
//releasing the lock so that other threads can get notifies
lock.unlock();
}
}Example of violations:
class SomeClass {
final ReentrantLock lock = new ReentrantLock()
def method() {
// violation
synchronized(lock) { }
}
}
class SomeClass {
final ReentrantLock lock = new ReentrantLock()
class SomeInnerClass {
def method() {
synchronized(lock) { }
}
}
}
class SomeClass {
// implicit typing
final def lock = new ReentrantLock()
def method() {
// violation
synchronized(lock) { }
}
}
class SomeClass {
// implicit typing
final def lock = new Object[0] // correct idiom
def method() {
return new Runnable() {
final def lock = new ReentrantLock() // shadows parent from inner class
public void run() {
// violation
synchronized(lock) { }
}
}
}
}
class SomeClass {
// implicit typing
final def lock = new Object[0] // correct idiom
class SomeInnerClass {
final def lock = new ReentrantLock() // shadows parent from inner class
def method() {
// violation
synchronized(lock) { }
}
}
}