[FFmpeg-devel] [PATCH 1/2] lavc: add JNI support

[wm4]

On Tue, 1 Mar 2016 20:10:50 +0100
Matthieu Bouron <matthieu.bouron at gmail.com> wrote:

> On Tue, Mar 01, 2016 at 07:56:30PM +0100, wm4 wrote:
> > On Tue, 1 Mar 2016 19:52:08 +0100
> > Matthieu Bouron <matthieu.bouron at gmail.com> wrote:
> >   
> > > On Fri, Feb 26, 2016 at 05:36:40PM +0100, Matthieu Bouron wrote:  
> > > > On Fri, Feb 26, 2016 at 4:41 PM, Matthieu Bouron <matthieu.bouron at gmail.com>
> > > > wrote:
> > > >     
> > > > > On Mon, Feb 22, 2016 at 12:20:35PM +0100, Matthieu Bouron wrote:    
> > > > > > From: Matthieu Bouron <matthieu.bouron at stupeflix.com>
> > > > > >    
> > > > >    
> > > > 
> > > > [...]
> > > > 
> > > >     
> > > > >
> > > > > Patch updated with the following differences:
> > > > >   * fix of switch/case code style
> > > > >   * removal of a miss declaration of FFJNIField enum as a global variable
> > > > >
> > > > >    
> > > > Patch updated with the following differences:
> > > >   * fixes a few typo in comments
> > > >   * fixes a if statement in ff_jni_init_jfields    
> > > 
> > > Patch updated with the following differences:
> > >   * fixes a few typo in comments and message logs
> > >   * add missing .so at end of library names when trying to find
> > >   JNI_GetCreatedVMs symbol (also add libart.so)
> > >   * reintroduce public functions that allow the user to set the Java
> > >   virtual machine (av_jni_(set,get)_java_vm) as the private C++
> > >   JniInvocation wrapper is not available on all devices (android >= 4.4)  
> > 
> > I'm wondering if the VM should be stored per AVCodecContext. (Since it
> > has to be set explicitly again by the user.)  
> 
> I think it is fine to store one VM for all the AVCodecContext as it will
> be the same during all the lifetime of the application. I should also
> enforce that the VM cannot be changed afterwards.
> 
> av_jni_set_java_vm stores the Java VM pointer locally in jni.c and not in
> ffjni.c and it is retrieved in jni.c using av_jni_get_java_vm. I've done
> it that way because if at some point we are to include ffjni.c from
> libavformat it won't work (it will only set the java vm in the libavcodec
> memory space).

The problem is that this is not library-safe. What if two libs within
the process (which both are using libavcodec) are setting a different
VM?