Hotspot VM Overview / JNI_CreateJavaVM

openjdk.java.net/groups/hotspot/docs/RuntimeOverview.html#VM%20Lifecycle|outline

JNI_CreateJavaVM

The JNI invocation method performs, the following:

1. Ensures that no two threads call this method at the same time and that no two VM instances are created in the same process. Noting that a VM cannot be created in the same process space once a point in initialization is reached, “point of no return”. This is so because the VM creates static data structures that cannot be re-initialized, at this time.

2. Checks to make sure the JNI version is supported, and the ostream is initialized for gc logging. The OS modules are initialized such as the random number generator, the current pid, high-resolution time, memory page sizes, and the guard pages.

3. The arguments and properties passed in are parsed and stored away for later use. The standard java system properties are initialized.

4. The OS modules are further created and initialized, based on the parsed arguments and properties, are initialized for synchronization, stack, memory, and safepoint pages. At this time other libraries such as libzip, libhpi, libjava, libthread are loaded, signal handlers are initialized and set, and the thread library is initialized.

5. The output stream logger is initialized. Any agent libraries (hprof, jdi) required are initialized and started.

6. The thread states and the thread local storage (TLS), which holds several thread specific data required for the operation of threads, are initialized.

7. The global data is initialized as part of the I phase, such as event log, OS synchronization primitives, perfMemory (performance memory), chunkPool (memory allocator).

8. At this point, we can create Threads. The Java version of the main thread is created and attached to the current OS thread. However this thread will not be yet added to the known list of the Threads. The Java level synchronization is initialized and enabled.

9. The rest of the global modules are initialized such as theBootClassLoader, CodeCache, Interpreter, Compiler, JNI,SystemDictionary, and Universe. Noting that, we have reached our “point of no return”, ie. We can no longer create another VM in the same process address space.

10. The main thread is added to the list, by first locking the Thread_Lock. The Universe, a set of required global data structures, is sanity checked. The VMThread, which performs all the VM's critical functions, is created. At this point the appropriate JVMTI events are posted to notify the current state.

11. The following classes java.lang.String, java.lang.System,java.lang.Thread, java.lang.ThreadGroup,java.lang.reflect.Method, java.lang.ref.Finalizer,java.lang.Class, and the rest of the System classes, are loaded and initialized. At this point, the VM is initialized and operational, but not yet fully functional.

12. The Signal Handler thread is started, the compilers are initialized and the CompileBroker thread is started. The other helper threads StatSampler and WatcherThreads are started, at this time the VM is fully functional, the JNIEnv is populated and returned to the caller, and the VM is ready to service new JNI requests.