[pron]

Why do you assume that the JVM adds overhead? While in some cases a program is better served by C/C++ manual memory management and fine-tuned memory alignment, this is not usually the case.

You can think of the JVM as a very good optimizing compiler that compiles your program when you load it in a way that's tailored to your environment.

Also, when it comes to concurrency support, the JVM is usually years ahead of C++ (lock-free data structures, etc.). If you're doing concurrency, the JVM is usually a better target than C++.

[kasey_junk]

Not to mention the kinds of programs that would most benefit from lightweight threads are high connection count servers. Precisely the kinds of applications where the JVM weaknesses are most hidden (startup time, base level latency, etc).