The Moth

A great number of posts in the NETCF newsgroup are memory related. This is no surprise, given the constraints of devices (as opposed to the PC), and most posts somehow end with a variation on this tail question: "[...] is this a known memory leak with the CF?"

Given that there are plenty of CF resources to help you in this area, I thought I'd gather them up in a single place for future reference.

1. The first thing to do is make sure you are running the latest released CF version. Contrary to popular misconception, this is (today) CF 1.0 SP3. For CF version info (numbers, how to determine it, where to get it etc) please go here.

2. Doing the above is good regardless of anything else; the second thing to address is "Are you really having memory troubles?” Can you reproduce a sample where you get an OutOfMemoryException? If not, why do you think there is a memory leak! This is common to devs still new to the managed world, where resources are not reclaimed immediately after they have been used. A rule of thumb applies here: if an object you are using offers the Dispose method, call it when you have finished using the object.

3. So we've now reached the case where you can reproduce a sample that throws the OutOfMemoryException (or at the very least that is what your main app does). Before you start pointing fingers at the Garbage Collector, please understand how the GC works (note the significant differences compared to the Full Fx version i.e. not generational, code pitching etc). Once you've done that, understand some v1.0 issues and workarounds, including when to call GC.Collect

4. "Fine with all the theory, but how do I measure?" You have a number of options available (please use them):
- Call GC.GetTotalMemory(false)
- PInvoke GlobalMemoryStatus (FAQ 6.5)
- Monitor Perf Statistics/Counters (do follow the links from that blog entry)
- Device's control panel applet e.g. on WinCE emulator, Start->Settings->System look under the Memory tab for memory info and how to change the memory distribution (check out the FAQ on the WinCE memory division between Storage and Program memory)

5. For completeness, here is a link to an in-depth article on WinCE memory management. The main takeaway, if you are coming from a desktop background, is that each process in CE has a limit of 32MB virtual address space; so forget loading all those massive bitmaps in memory.

6. On very extremely rare occasions you may possibly observe a "Low Memory Dialog" rather than an OutOfMemoryException. This is the OOM dialog which shouldn't, but may, pop-up before a managed exception is thrown. That is an indication that you are stressing the system but, if you really want to, you can remove the OOM component from your device - assuming you have control of the image with Platform Builder (if you are in that situation, check out the SetOomEvent and registry entries).

7. Finally, if none of the links above take you to long documents with many numbers, go read Advanced Memory article on CF 2.0