Question: How does JVM interact with profilers?

Answer: The Java Virtual Machine has Profiler Interface (JVMPI) in the Java 2 SDK, Standard Edition. This interface is an experimental feature in the Java 2 SDK. The JVMPI is not yet a standard profiling interface. It is intended for tools vendors to develop profilers that work in conjunction with Sun's Java virtual machine implementation.
"The JVMPI is a two-way function call interface between the Java virtual machine and an in-process profiler agent. On one hand, the virtual machine notifies the profiler agent of various events, corresponding to, for example, heap allocation, thread start, etc. On the other hand, the profiler agent issues controls and requests for more information through the JVMPI. For example, the profiler agent can turn on/off a specific event notification, based on the needs of the profiler front-end.
The profiler front-end may or may not run in the same process as the profiler agent. It may reside in a different process on the same machine, or on a remote machine connected via the network. The JVMPI does not specify a standard wire protocol. Tools vendors may design wire protocols suitable for the needs of different profiler front-ends.
A profiling tool based on JVMPI can obtain a variety of information such as heavy memory allocation sites, CPU usage hot-spots, unnecessary object retention, and monitor contention, for a comprehensive performance analysis.
JVMPI supports partial profiling, i.e. a user can selectively profile an application for certain subsets of the time the virtual machine is up and can also choose to obtain only certain types of profiling information.
In the current version of JVMPI, only one agent per virtual machine can be supported." Details can be found here:
http://java.sun.com/j2se/1.4.1/docs/guide/jvmpi/jvmpi.html