ANDROID: Store JNI environment in a thread local variable

This avoids to query JVM every time we need to do a JNI call.
A different environment is attached to each thread, hence the TLS
variable.

backends/platform/android/asset-archive.cpp

@@ -24,6 +24,12 @@
 #include <sys/types.h>
 #include <unistd.h>
 
+#include <android/asset_manager.h>
+#include <android/asset_manager_jni.h>
+
+#include "backends/platform/android/jni-android.h"
+#include "backends/platform/android/asset-archive.h"
+
 #include "common/str.h"
 #include "common/stream.h"
 #include "common/util.h"
@@ -31,12 +37,6 @@
 #include "common/debug.h"
 #include "common/textconsole.h"
 
-#include "backends/platform/android/jni-android.h"
-#include "backends/platform/android/asset-archive.h"
-
-#include <android/asset_manager.h>
-#include <android/asset_manager_jni.h>
-
 class AssetInputStream : public Common::SeekableReadStream {
 public:
 	AssetInputStream(AAssetManager *as, const Common::String &path);

backends/platform/android/jni-android.cpp

@@ -58,6 +58,8 @@ jint JNICALL JNI_OnLoad(JavaVM *vm, void *) {
 	return JNI::onLoad(vm);
 }
 
+pthread_key_t JNI::_env_tls;
+
 JavaVM *JNI::_vm = 0;
 jobject JNI::_jobj = 0;
 jobject JNI::_jobj_audio_track = 0;
@@ -141,6 +143,10 @@ JNI::~JNI() {
 }
 
 jint JNI::onLoad(JavaVM *vm) {
+	if (pthread_key_create(&_env_tls, NULL)) {
+		return JNI_ERR;
+	}
+
 	_vm = vm;
 
 	JNIEnv *env;
@@ -148,6 +154,10 @@ jint JNI::onLoad(JavaVM *vm) {
 	if (_vm->GetEnv((void **)&env, JNI_VERSION_1_2))
 		return JNI_ERR;
 
+	if (pthread_setspecific(_env_tls, env)) {
+		return JNI_ERR;
+	}
+
 	jclass cls = env->FindClass("org/scummvm/scummvm/ScummVM");
 	if (cls == 0)
 		return JNI_ERR;
@@ -158,8 +168,8 @@ jint JNI::onLoad(JavaVM *vm) {
 	return JNI_VERSION_1_2;
 }
 
-JNIEnv *JNI::getEnv() {
+JNIEnv *JNI::fetchEnv() {
-	JNIEnv *env = 0;
+	JNIEnv *env;
 
 	jint res = _vm->GetEnv((void **)&env, JNI_VERSION_1_2);
 
@@ -168,6 +178,8 @@ JNIEnv *JNI::getEnv() {
 		abort();
 	}
 
+	pthread_setspecific(_env_tls, env);
+
 	return env;
 }
 
@@ -180,9 +192,16 @@ void JNI::attachThread() {
 		LOGE("AttachCurrentThread() failed: %d", res);
 		abort();
 	}
+
+	if (pthread_setspecific(_env_tls, env)) {
+		LOGE("pthread_setspecific() failed");
+		abort();
+	}
 }
 
 void JNI::detachThread() {
+	pthread_setspecific(_env_tls, NULL);
+
 	jint res = _vm->DetachCurrentThread();
 
 	if (res != JNI_OK) {

backends/platform/android/jni-android.h

@@ -26,6 +26,7 @@
 
 #include <jni.h>
 #include <semaphore.h>
+#include <pthread.h>
 
 #include "common/fs.h"
 #include "common/archive.h"
@@ -59,7 +60,14 @@ public:
 
 	static jint onLoad(JavaVM *vm);
 
-	static JNIEnv *getEnv();
+	static inline JNIEnv *getEnv() {
+		JNIEnv *env = (JNIEnv*) pthread_getspecific(_env_tls);
+		if (env != nullptr) {
+			return env;
+		}
+
+		return fetchEnv();
+	}
 
 	static void attachThread();
 	static void detachThread();
@@ -102,6 +110,8 @@ public:
 	static bool isDirectoryWritableWithSAF(const Common::String &dirPath);
 
 private:
+	static pthread_key_t _env_tls;
+
 	static JavaVM *_vm;
 	// back pointer to (java) peer instance
 	static jobject _jobj;
@@ -172,6 +182,8 @@ private:
 	static Common::U32String convertFromJString(JNIEnv *env, const jstring &jstr);
 
 	static PauseToken _pauseToken;
+
+	static JNIEnv *fetchEnv();
 };
 
 inline bool JNI::haveSurface() {