Is it thread-safe to increment an Int32 in a Timer callback?

Question

I want to increment an integer that gets incremented in a timer event handler and read by the main and other worker threads i.e. one writer thread and multiple reader threads. Will it be thread-safe?

I have a timer in my application that runs every 5 seconds:

MyClock = new System.Threading.Timer(
    new TimerCallback(this.Ticker), null, Timeout.Infinite, Timeout.Infinite );

that I turn on like this:

MyClock.Change(5000, 5000);

If I increment an integer in the Ticker handler like this:

tickerCounter++;

can I then do a read-only access from main thread or worker threads of the same application? Will it be thread safe? Is there any chance of the reader to read a partial value, or causing a threading exception?

Answer 1

Incrementing like this

tickerCounter++;

in multiple threads, without locking, is not threadsafe. You can use the Interlocked class to perform lock-free, threadsafe incrementing.

If only a single thread is modifying the value, with many threads reading the value, then tickerCounter++ is threadsafe in the sense that no thread will ever suffer a partial read. Of course there is still a race condition, but even if you use Interlocked, there would be a race.