I have a C++ codebase, in which I'm using JNI to create a JVM and occasionally interact with a library implemented in Java. I'm curious whether, in this use case, Java's garbage collector will still reliably run and clean up?
Most of the information that I find online about JNI seems to be about the "opposite" use case, where people generally appear to have mainly Java code, which sometimes interacts with native code through JNI. For such a use case, I find for example the following online:
The automatic garbage collection of local references that are no longer in scope prevents memory leaks in most situations. This automatic garbage collection occurs when a native thread returns to Java (native methods) or detaches from the JVM (Invocation API). Local reference memory leaks are possible if automatic garbage collection does not occur. A memory leak might occur if a native method does not return to the JVM, or if a program that uses the Invocation API does not detach from the JVM.
I'm not sure what exactly "returns to Java" in this context means. Is just occasionally calling into Java-based methods from C++ sufficient, does that already count as "returning to Java"? If not, are there any ways to make sure that the garbage collector gets a chance to run in my use case?
The JVM created with JNI is a full JVM, including GC.
Think of it this way: The java command that you normally use to run Java programs, is nothing but a small JNI program that creates a JVM, locates the class named on the command-line, and makes a static call to the main(String[]) method.