lavc/ffjni: replace ff_jni_{attach,detach} with ff_jni_get_env

If a JNI environment is not already attached to the thread where the
MediaCodec calls are made the current implementation will attach /
detach an environment for each MediaCodec call wasting some CPU time.

ff_jni_get_env replaces ff_jni_{attach,detach} by permanently attaching
an environment (if it is not already the case) to the current thread.
The environment will be automatically detached at the thread destruction
using a pthread_key callback.

Saves around 5% of CPU time (out of 20%) while decoding a stream with
MediaCodec.

1 files changed, 5 insertions, 10 deletions

diff --git a/libavcodec/ffjni.h b/libavcodec/ffjni.h
index 990c7b9c3f..6027bac0ab 100644
--- a/libavcodec/ffjni.h
+++ b/libavcodec/ffjni.h
@@ -26,7 +26,10 @@
 #include <jni.h>
 
 /*
- * Attach a JNI environment to the current thread.
+ * Attach permanently a JNI environment to the current thread and retrieve it.
+ *
+ * If successfully attached, the JNI environment will automatically be detached
+ * at thread destruction.
  *
  * @param attached pointer to an integer that will be set to 1 if the
  * environment has been attached to the current thread or 0 if it is
@@ -34,15 +37,7 @@
  * @param log_ctx context used for logging, can be NULL
  * @return the JNI environment on success, NULL otherwise
  */
-JNIEnv *ff_jni_attach_env(int *attached, void *log_ctx);
-
-/*
- * Detach the JNI environment from the current thread.
- *
- * @param log_ctx context used for logging, can be NULL
- * @return 0 on success, < 0 otherwise
- */
-int ff_jni_detach_env(void *log_ctx);
+JNIEnv *ff_jni_get_env(void *log_ctx);
 
 /*
  * Convert a jstring to its utf characters equivalent.