Do Threads Add A Lot Of Overhead To An App?

Question

As my app matures, I find myself finding more and more uses for threads. By now I must have about 25 threads, all doing important things and working together in symphony.

I notice however that my app is sitting around 15.5MB resident. Compared to the browser (+/-35MB) I feel pretty safe, but I do notice the resident size of my app ever increasing.

The question is, how much overhead is involved with adding a thread?

I'm also wondering if the synchronized keyword encounters more and more latency with each new thread that is present?

Thanks!

Answer 1

For some perspective here, a freshly launched Browser app has about 20 threads running. Having 25 threads is not utterly unreasonable. It really depends on what you are doing with them.

app_1     17309 67    182452 27944 ffffffff 00000000 S com.android.browser
app_1     17310 17309 182452 27944 ffffffff 00000000 S HeapWorker
app_1     17311 17309 182452 27944 ffffffff 00000000 S Signal Catcher
app_1     17312 17309 182452 27944 ffffffff 00000000 S JDWP
app_1     17313 17309 182452 27944 ffffffff 00000000 S Compiler
app_1     17314 17309 182452 27944 ffffffff 00000000 S Binder Thread #
app_1     17315 17309 182452 27944 ffffffff 00000000 S Binder Thread #
app_1     17317 17309 182452 27944 ffffffff 00000000 S CookieSyncManag
app_1     17319 17309 182452 27944 ffffffff 00000000 S WebViewCoreThre
app_1     17321 17309 182452 27944 ffffffff 00000000 S AsyncTask #1
app_1     17322 17309 182452 27944 ffffffff 00000000 S AsyncTask #2
app_1     17323 17309 182452 27944 ffffffff 00000000 S WebViewCoreThre
app_1     17324 17309 182452 27944 ffffffff 00000000 S http0
app_1     17325 17309 182452 27944 ffffffff 00000000 S http1
app_1     17326 17309 182452 27944 ffffffff 00000000 S http2
app_1     17327 17309 182452 27944 ffffffff 00000000 S http3
app_1     17328 17309 182452 27944 ffffffff 00000000 S WebViewWorkerTh
app_1     17329 17309 182452 27944 ffffffff 00000000 S AsyncTask #3
app_1     17330 17309 182452 27944 ffffffff 00000000 S AsyncTask #4
app_1     17332 17309 182452 27944 ffffffff 00000000 S AsyncTask #5

Answer 2

Threads are very useful but at the same time they can be a menace. I am working on a project to check threats presented by an application. If you run top via the adb shell, it specifically tells you how many threads an application may be running.

You will see processor usage is directly proportional to the number of threads. That pretty much means more the number of threads higher is the overhead. Though they seem to keep your activity free from getting stuck at time it may become a real pain to synchronize their actions and then you may have deadlock, not very pretty. Also multiple no of threads raise suspicion about the behaviour of an application. Hence they should be utilized in the spirit they are meant to be.

Answer 3

If you're creating and destroying threads over and over again then yes it will be taxing and cause overhead. You can eliminate that by utilizing the ThreadPool, which keeps a cache of threads available for execution. Otherwise, threads are the way to go over processes.

You may want to think of practical adjustments to the architecture. For example, if you're keeping multiple threads alive for the sake of having a responsive UI, (i.e. waiting for input) even if a particular thread would only be used after five menu jumps then maybe its not necessary to keep the threads alive all the time. I have rarely used 15 distinct threads in a single application, even when that application ran a massive machine tool....(I had repeat worker threads going though). Don't forget that threads still have to be scheduled so don't keep them around needlessly.

Lastly, make sure that you're not running into the same old problems with parallel program; avoid deadlocks etc....