I am making a Windows JNI .dll. I am trying to determine whether the JVM can ever make concurrent calls to the same native function. Here is the Java code I wrote:
public class TestThreads implements Runnable
{
public void run()
{
MyJNIClass.f(); // Call 'native' static member function
}
public static void main(String[] args)
{
for (int k = 0; k < 20; ++k)
new Thread(new TestThreads()).run();
}
}
On the native side, the function MyJNIClass.f() is implemented like so:
#include <jni.h>
#include <windows.h>
#include <iostream>
extern "C"
{
JNIEXPORT void JNICALL Java_MyJNIClass_f(JNIEnv * env, jclass clazz)
{
std::cout << GetCurrentThreadId() << ", " << GetCurrentThread() << std::endl;
Sleep(500);
}
}
The output from the native function indicates that all the calls are running from the same Win32 thread:
5196, 0xfffffffe
5196, 0xfffffffe
5196, 0xfffffffe
5196, 0xfffffffe
5196, 0xfffffffe
5196, 0xfffffffe
5196, 0xfffffffe
5196, 0xfffffffe
5196, 0xfffffffe
...
...and each of these lines pops out about half a second after the previous one.
So is the only way to get the native side to use multiple threads like the JVM to create a worker thread on the native/DLL side and then return immediately!?!?
Peter Lawrey :
You have only one thread which is \"main\" which was created for you.\n\nI suspect you intended to call start(); which calls run(); in a new thread, instead of reusing the current thread.",
2013-06-20T00:01:48