Pattern: Synchronized on string
Issue: -
Synchronization on a String field can lead to deadlock. Constant strings are interned and shared across all other classes loaded by the JVM. Thus, this could is locking on something that other code might also be locking. This could result in very strange and hard to diagnose blocking and deadlock behavior.
Examples:
class SomeClass {
final String stringLock = "stringLock"
def method() {
// violation
synchronized(stringLock) { }
}
}
class SomeClass {
final String stringLock = "stringLock"
class SomeInnerClass {
def method() {
synchronized(stringLock) { }
}
}
}
class SomeClass {
// implicit typing
final def stringLock = "stringLock"
def method() {
// violation
synchronized(stringLock) { }
}
}
class SomeClass {
// implicit typing
final def lock = new Object[0] // correct idiom
def method() {
return new Runnable() {
final def lock = "" // shadows parent from inner class
public void run() {
// violation
synchronized(stringLock) { }
}
}
}
}
class SomeClass {
// implicit typing
final def lock = new Object[0] // correct idiom
class SomeInnerClass {
final def lock = "" // shadows parent from inner class
def method() {
// violation
synchronized(stringLock) { }
}
}
}