I asked a similar question the other day but wasn't satisfied with the response, mainly because the code I supplied had some issues that people focused on.
Basically, what is the best practice for locking private members in Java? Assuming each private field can only be manipulated in isolation and never together (like in my Test class example below), should you lock each private field directly (example 1), or should you use a general lock object per private field you wish to lock (example 2)?
Example 1: Lock private fields directly
class Test {
private final List<Object> xList = new ArrayList<Object>();
private final List<Object> yList = new ArrayList<Object>();
/* xList methods */
public void addToX(Object o) {
synchronized(xList) {
xList.add(o);
}
}
public void removeFromX(Object o) {
synchronized(xList) {
xList.remove(o);
}
}
/* yList methods */
public void addToY(Object o) {
synchronized(yList) {
yList.add(o);
}
}
public void removeFromY(Object o) {
synchronized(yList) {
yList.remove(o);
}
}
}
Example 2: Use lock objects per private field
class Test {
private final Object xLock = new Object();
private final Object yLock = new Object();
private List<Object> xList = new ArrayList<Object>();
private List<Object> yList = new ArrayList<Object>();
/* xList methods */
public void addToX(Object o) {
synchronized(xLock) {
xList.add(o);
}
}
public void removeFromX(Object o) {
synchronized(xLock) {
xList.remove(o);
}
}
/* yList methods */
public void addToY(Object o) {
synchronized(yLock) {
yList.add(o);
}
}
public void removeFromY(Object o) {
synchronized(yLock) {
yList.remove(o);
}
}
}