Android :: C++ Code Problem In NDK - Nexus One

I got a strange problem when I run my app on Nexus One, Android 2.2. In my app, I used a native .so lib, built under NDK. In Java code, I have 2 threads: one UI thread, one to run codes from native so lib, and then updates the UI with the result data.

In C++ code, I have a global variable "int count", which records the times a specific method "myMethod" is called, and the count is increased by one every time "myMethod" is called.

When I run my app in Nexus One, with Android 2.2, the strange problem occured. In my log, the count is 1, 2, 3, and then a message says "08-24 12:32:57.961: DEBUG/dalvikvm(19244): GC_FOR_MALLOC freed 267 objects / 13712 bytes in 48ms". After this GC_FOR_MALLOC event, my count is reset, starting from 1 again, and then 2, 3, 4...Then it seems that there are 2 threads running the same "myMethod", each outputs its own trace, mixed with each others trace randomly.

For example, the trace can be: 1, 2, 3, GC_FOR_MALLOC, 1, 2, 3, 4, 5, GC_FOR_MALLOC, 4, 5, 6, GC_FOR_MALLOC, 6, 7...

When I run the same app with exactly the same code on Android Emulator, 2.1 or 2.2, the problem never showed up, and there are no GC_FOR_MALLOC event on emulator.