Cool... thank you for your help.
--jason
On 11-Jan-99 Juergen Kreileder wrote:
>>>>>> Jason Dillon writes:
>
> Jason> Does this apply to native methods as well? The docs do not
> Jason> really mention anything about native methods (not in that
> Jason> section anyways). I am wondering if it is safe to assume
> Jason> that marking a native method as synchronized will
> Jason> automagicly protect the object from access by other threads
> Jason> or if I have to explicitly protect the method in the native
> Jason> code.
>
> Yes, this applies to native methods as well and at least the JDK
> implements it correctly.
>
> Here's a little test program:
>
> C.java:
> class C
> {
> static {
> System.loadLibrary("synctest");
> }
>
> native synchronized void ok();
> native void bad();
>
> public static void main(String[] args)
> {
> C c = new C();
> c.ok();
> System.out.println("--------------");
> c.bad();
> }
> }
>
> synctest.c:
>#include <stdlib.h>
>#include "C.h"
>
> JNIEXPORT void JNICALL
> Java_C_ok(JNIEnv* env, jobject this)
> {
> jclass cls = (*env)->FindClass(env, "C");
> jmethodID mid = (*env)->GetMethodID(env, cls, "notify", "()V");
> (*env)->CallObjectMethod(env, this, mid);
> if ((*env)->ExceptionOccurred(env)) {
> (*env)->ExceptionDescribe(env);
> }
> }
>
> JNIEXPORT void JNICALL
> Java_C_bad (JNIEnv* env, jobject this)
> {
> jclass cls = (*env)->FindClass(env, "C");
> jmethodID mid = (*env)->GetMethodID(env, cls, "notify", "()V");
> (*env)->CallObjectMethod(env, this, mid);
> if ((*env)->ExceptionOccurred(env)) {
> (*env)->ExceptionDescribe(env);
> }
> }
>
> The call to c.ok() should be ok but c.bad() should fail, i.e. the correct
> output is:
> $ LD_LIBRARY_PATH=. java C
> --------------
> java.lang.IllegalMonitorStateException: current thread not owner
> at C.main(C.java:16)
>
>
> Juergen
>
> Jason> On 11-Jan-99 Juergen Kreileder wrote:
> >>>>>>> Jason Dillon writes:
> >>
> Jason> This is not really java-linux specific, but this is the
> Jason> only java related group that I am subscribed to. I am
> Jason> wondering if a native method is specified as synchronized
> Jason> if the jvm will perform the proper MontiorEnter &
> Jason> MonitorExit calls or if I should call them in the native
> Jason> method.
> >>
> Jason> So for example... does:
> >>
> Jason> native public synchronized byte[] getBytes ();
> >>
> Jason> imply:
> >>
> Jason> JNIEXPORT jbyteArray JNICALL Java_<Package>_<Class>_getBytes
> Jason> (JNIEnv *env, jobject jthis)
> Jason> {
> Jason> (*env)->MonitorEnter(env, jthis);
> Jason> /* do something */
> Jason> (*env)->MonitorExit(env, jthis);
> >>
> Jason> return /* some jbyteArray */;
> Jason> }
> >>
> >> Not exactly, the method indeed is synchronized but the synchronization
> >> is part of the method invocation and return. Section 7.14 of the
> >> virtual machine specification has more details about that:
> >> http://java.sun.com/docs/books/vmspec/html/Compiling.doc.html#6530
> >>
> >>
> >> Juergen
> >>
> >> --
> >> Juergen Kreileder, Universitaet Dortmund, Lehrstuhl Informatik V
> >> Baroper Strasse 301, D-44221 Dortmund, Germany
> >> Phone: ++49 231/755-5806, Fax: ++49 231/755-5802
