Fix crash in OpenGLDriver::destroyStream

[z3moon]

Fixes a SIGSEGV crash that occurs during
ExternalStreamManagerAndroid::release() when users provide a custom Platform instance during Engine creation.

When a custom Platform is used, ExternalStreamManagerAndroid is instantiated on the application's thread. Its constructor was caching a C++ reference (VirtualMachineEnv& mVm) to the thread_local VirtualMachineEnv instance belonging to the application thread.

Later, when the Filament backend thread executed release(), it accessed this cached reference. This caused the backend thread to retrieve the JNIEnv* from the application thread's thread_local instance, and subsequently call env->DeleteGlobalRef(). A thread must use its own JNIEnv pointer, so using the application thread's pointer from the backend thread resulted in a crash.

BUGS=[489814416]

[poweifeng]

there was a similar fix for PerformanceHIntManager here: cff9585

Can we do something similar here? (Like initialize ExternalStreamManagerAndroid on the backend thread).

[z3moon]

there was a similar fix for PerformanceHIntManager here: cff9585

Can we do something similar here? (Like initialize ExternalStreamManagerAndroid on the backend thread).

In the current Filament design, a stream is created in the application thread via createStreamNative or createStreamAcquired, and they're destroyed in the backend thread via destroyStream. I think this is because the application thread (Java) should directly increase the global reference of the given surface texture instance. (it wouldn't be valid in the backend thread). So we should allow both threads to have its own JNIEnv.

[pixelflinger]

VirtualMachineEnv::get() is documented as "must be called on the backend thread"
This is also the case for VirtualMachineEnv::getEnvironment().

I think what should happen instead is that ExternalStreamManager should always be created from the backend thread (this broke, guess, when we allowed custom Platforms).

And, we should use VirtualMachineEnv::getThreadEnvironment() to get a JNIEnv from any thread.

[z3moon]

Yeah I moved the creation to the backend side.