Question

i have a class that starts new threads, and they use a handler to write a an array in the ui thread,they are thread safe.

What if i start those threads from a timer task, are they still threadsafe with the ui thred?

Thank you!

Answer 1

If the Handler objects are bound to the UI thread, it is safe to update the array in the Handler (assuming that the array is also bound to the UI thread).

Check the Handler documentation, especially this part:

A Handler allows you to send and process Message and Runnable objects associated with a thread’s MessageQueue. Each Handler instance is associated with a single thread and that thread’s message queue. When you create a new Handler, it is bound to the thread / message queue of the thread that is creating it — from that point on, it will deliver messages and runnables to that message queue and execute them as they come out of the message queue.

There are two main uses for a Handler: (1) to schedule messages and runnables to be executed as some point in the future; and (2) to enqueue an action to be performed on a different thread than your own.

It states that the Handler code is executed on the thread it belongs to.