what does methods named '*Locked()' mean in Activity related classes?

Question

I noticed that there are lots of use of the methods named '*Locked()' while I am looking through Android framework codes. I wonder what 'Locked' means and what features those methods are reflecting to.

For example, there are a number of methods named in such way in Activity related classes.

android/frameworks/base/services/java/com/android/server/am/ActivityStack.java

• startActivityLocked()
• ensureActivitiesVisibleLocked()
• resumeTopActivityLocked()

Thank you for your help in advance! :)

Answer 1

That means the method is multithread-safe.

Answer 2

You can find code from ActivityManagerService.class like below:

synchronized (this) {
    dumpActivitiesLocked(fd, pw, args, opti, true, dumpClient, null);
}

or some code like that:

synchronized (this) {
    methodA();
}
methodA() {
    dumpActivitiesLocked(fd, pw, args, opti, true, dumpClient, null);
}

So the methods named *Locked means the method is not multithread-safe, in ActivityManagerService.class, you should use synchronized (this) make sure the multithread-safe.