Fix warning about recursive loading of libmedia_jni.so

JNI register methods were resolving classes to initialize fieldID's
and methodID's for native JNI use. Those classes may have static
initializers which call System.loadLibrary("libmedia_jni.so"), but the
library is already in the process of being loaded.

Bug: 180829511
Test: TH
Test: boot blueline observe no output from "adb logcat -d | grep recursive"
Change-Id: I47d40bc06457a9550bd5855f6f8d031ddc465b47

4 files changed, 205 insertions, 375 deletions

diff --git a/media/jni/android_media_JetPlayer.cpp b/media/jni/android_media_JetPlayer.cpp
index 481f80b278f8..10a5b586c2b9 100644
--- a/media/jni/android_media_JetPlayer.cpp
+++ b/media/jni/android_media_JetPlayer.cpp
@@ -43,12 +43,34 @@ struct fields_t {
     jfieldID  nativePlayerInJavaObj; // stores in Java the native JetPlayer object
 };
 
-static fields_t javaJetPlayerFields;
+static fields_t javaJetPlayerFields {};
 
+#define JAVA_NATIVEJETPLAYERINJAVAOBJ_FIELD_NAME "mNativePlayerInJavaObj"
+#define JAVA_NATIVEJETPOSTEVENT_CALLBACK_NAME "postEventFromNative"
+
+static void initializeJavaIDs(JNIEnv* env) {
+    static std::once_flag sJniInitialized;
+
+    std::call_once(sJniInitialized, [](JNIEnv* env) {
+        // Get the JetPlayer java class
+        jclass jetPlayerClass = FindClassOrDie(env, kClassPathName);
+        javaJetPlayerFields.jetClass = MakeGlobalRefOrDie(env, jetPlayerClass);
+
+        // Get the mNativePlayerInJavaObj variable field
+        javaJetPlayerFields.nativePlayerInJavaObj =
+                GetFieldIDOrDie(env, jetPlayerClass, JAVA_NATIVEJETPLAYERINJAVAOBJ_FIELD_NAME, "J");
+
+        // Get the callback to post events from this native code to Java
+        javaJetPlayerFields.postNativeEventInJava = GetStaticMethodIDOrDie(env,
+                javaJetPlayerFields.jetClass, JAVA_NATIVEJETPOSTEVENT_CALLBACK_NAME,
+                "(Ljava/lang/Object;III)V");
+    }, env);
+}
 
 // ----------------------------------------------------------------------------
 // ----------------------------------------------------------------------------
 
+
 /*
  * This function is called from JetPlayer instance's render thread
  */
@@ -79,6 +101,8 @@ static jboolean
 android_media_JetPlayer_setup(JNIEnv *env, jobject thiz, jobject weak_this,
     jint maxTracks, jint trackBufferSize)
 {
+    initializeJavaIDs(env);
+
     //ALOGV("android_media_JetPlayer_setup(): entering.");
     JetPlayer* lpJet = new JetPlayer(env->NewGlobalRef(weak_this), maxTracks, trackBufferSize);
 
@@ -511,28 +535,9 @@ static const JNINativeMethod gMethods[] = {
     {"native_clearQueue",  "()Z",                   (void *)android_media_JetPlayer_clearQueue},
 };
 
-#define JAVA_NATIVEJETPLAYERINJAVAOBJ_FIELD_NAME "mNativePlayerInJavaObj"
-#define JAVA_NATIVEJETPOSTEVENT_CALLBACK_NAME "postEventFromNative"
 
 
 int register_android_media_JetPlayer(JNIEnv *env)
 {
-    javaJetPlayerFields.jetClass = NULL;
-    javaJetPlayerFields.postNativeEventInJava = NULL;
-    javaJetPlayerFields.nativePlayerInJavaObj = NULL;
-
-    // Get the JetPlayer java class
-    jclass jetPlayerClass = FindClassOrDie(env, kClassPathName);
-    javaJetPlayerFields.jetClass = MakeGlobalRefOrDie(env, jetPlayerClass);
-
-    // Get the mNativePlayerInJavaObj variable field
-    javaJetPlayerFields.nativePlayerInJavaObj = GetFieldIDOrDie(env,
-            jetPlayerClass, JAVA_NATIVEJETPLAYERINJAVAOBJ_FIELD_NAME, "J");
-
-    // Get the callback to post events from this native code to Java
-    javaJetPlayerFields.postNativeEventInJava = GetStaticMethodIDOrDie(env,
-            javaJetPlayerFields.jetClass, JAVA_NATIVEJETPOSTEVENT_CALLBACK_NAME,
-            "(Ljava/lang/Object;III)V");
-
     return RegisterMethodsOrDie(env, kClassPathName, gMethods, NELEM(gMethods));
 }
diff --git a/media/jni/android_mtp_MtpDatabase.cpp b/media/jni/android_mtp_MtpDatabase.cpp
index 4efdcaccf7a1..ffed4747d3ea 100644
--- a/media/jni/android_mtp_MtpDatabase.cpp
+++ b/media/jni/android_mtp_MtpDatabase.cpp
@@ -32,6 +32,7 @@
 
 #include <android_runtime/AndroidRuntime.h>
 #include <android_runtime/Log.h>
+#include "core_jni_helpers.h"
 #include <jni.h>
 #include <media/stagefright/NuMediaExtractor.h>
 #include <nativehelper/JNIHelp.h>
@@ -48,6 +49,7 @@ using namespace android;
 
 // ----------------------------------------------------------------------------
 
+// MtpDatabase methods
 static jmethodID method_beginSendObject;
 static jmethodID method_endSendObject;
 static jmethodID method_rescanFile;
@@ -75,6 +77,7 @@ static jmethodID method_endCopyObject;
 static jmethodID method_getObjectReferences;
 static jmethodID method_setObjectReferences;
 
+// MtpDatabase fields.
 static jfieldID field_context;
 
 // MtpPropertyList methods
@@ -86,6 +89,59 @@ static jmethodID method_getDataTypes;
 static jmethodID method_getLongValues;
 static jmethodID method_getStringValues;
 
+// Initializer for the jfieldIDs and jmethodIDs above. This method must be invoked
+// before using these static fields and methods for JNI accesses.
+static void initializeJavaIDs(JNIEnv* env) {
+    static std::once_flag sJniInitialized;
+
+#define GET_METHOD_ID(name, jclass, signature)                              \
+    method_##name = GetMethodIDOrDie(env, jclass, #name, signature);
+
+    std::call_once(sJniInitialized, [](JNIEnv* env) {
+        const jclass mdb_class = FindClassOrDie(env, "android/mtp/MtpDatabase");
+        GET_METHOD_ID(beginSendObject, mdb_class, "(Ljava/lang/String;III)I");
+        GET_METHOD_ID(endSendObject, mdb_class, "(IZ)V");
+        GET_METHOD_ID(rescanFile, mdb_class, "(Ljava/lang/String;II)V");
+        GET_METHOD_ID(getObjectList, mdb_class, "(III)[I");
+        GET_METHOD_ID(getNumObjects, mdb_class, "(III)I");
+        GET_METHOD_ID(getSupportedPlaybackFormats, mdb_class, "()[I");
+        GET_METHOD_ID(getSupportedCaptureFormats, mdb_class, "()[I");
+        GET_METHOD_ID(getSupportedObjectProperties, mdb_class, "(I)[I");
+        GET_METHOD_ID(getSupportedDeviceProperties, mdb_class, "()[I");
+        GET_METHOD_ID(setObjectProperty, mdb_class, "(IIJLjava/lang/String;)I");
+        GET_METHOD_ID(getDeviceProperty, mdb_class, "(I[J[C)I");
+        GET_METHOD_ID(setDeviceProperty, mdb_class, "(IJLjava/lang/String;)I");
+        GET_METHOD_ID(getObjectPropertyList, mdb_class, "(IIIII)Landroid/mtp/MtpPropertyList;");
+        GET_METHOD_ID(getObjectInfo, mdb_class, "(I[I[C[J)Z");
+        GET_METHOD_ID(getObjectFilePath, mdb_class, "(I[C[J)I");
+        GET_METHOD_ID(openFilePath, mdb_class, "(Ljava/lang/String;Z)I");
+        GET_METHOD_ID(getThumbnailInfo, mdb_class, "(I[J)Z");
+        GET_METHOD_ID(getThumbnailData, mdb_class, "(I)[B");
+        GET_METHOD_ID(beginDeleteObject, mdb_class, "(I)I");
+        GET_METHOD_ID(endDeleteObject, mdb_class, "(IZ)V");
+        GET_METHOD_ID(beginMoveObject, mdb_class, "(III)I");
+        GET_METHOD_ID(endMoveObject, mdb_class, "(IIIIIZ)V");
+        GET_METHOD_ID(beginCopyObject, mdb_class, "(III)I");
+        GET_METHOD_ID(endCopyObject, mdb_class, "(IZ)V");
+        GET_METHOD_ID(getObjectReferences, mdb_class, "(I)[I");
+        GET_METHOD_ID(setObjectReferences, mdb_class, "(I[I)I");
+        field_context = GetFieldIDOrDie(env, mdb_class, "mNativeContext", "J");
+
+        const jclass mpl_class = FindClassOrDie(env, "android/mtp/MtpPropertyList");
+        GET_METHOD_ID(getCode, mpl_class, "()I");
+        GET_METHOD_ID(getCount, mpl_class, "()I");
+        GET_METHOD_ID(getObjectHandles, mpl_class, "()[I");
+        GET_METHOD_ID(getPropertyCodes, mpl_class, "()[I");
+        GET_METHOD_ID(getDataTypes, mpl_class, "()[I");
+        GET_METHOD_ID(getLongValues, mpl_class, "()[J");
+        GET_METHOD_ID(getStringValues, mpl_class, "()[Ljava/lang/String;");
+
+        return 0;
+    }, env);
+
+#undef GET_METHOD_ID
+}
+
 
 IMtpDatabase* getMtpDatabase(JNIEnv *env, jobject database) {
     return (IMtpDatabase *)env->GetLongField(database, field_context);
@@ -1280,6 +1336,7 @@ MtpProperty* MtpDatabase::getDevicePropertyDesc(MtpDeviceProperty property) {
 static void
 android_mtp_MtpDatabase_setup(JNIEnv *env, jobject thiz)
 {
+    initializeJavaIDs(env);
     MtpDatabase* database = new MtpDatabase(env, thiz);
     env->SetLongField(thiz, field_context, (jlong)database);
     checkAndClearExceptionFromCallback(env, __FUNCTION__);
@@ -1314,69 +1371,9 @@ static const JNINativeMethod gMtpPropertyGroupMethods[] = {
     {"format_date_time",        "(J)Ljava/lang/String;",
                                         (void *)android_mtp_MtpPropertyGroup_format_date_time},
 };
-
-#define GET_METHOD_ID(name, jclass, signature)                              \
-    method_##name = env->GetMethodID(jclass, #name, signature);             \
-    if (method_##name == NULL) {                                            \
-        ALOGE("Can't find " #name);                                         \
-        return -1;                                                          \
-    }                                                                       \
-
+                                                                   \
 int register_android_mtp_MtpDatabase(JNIEnv *env)
 {
-    jclass clazz;
-
-    clazz = env->FindClass("android/mtp/MtpDatabase");
-    if (clazz == NULL) {
-        ALOGE("Can't find android/mtp/MtpDatabase");
-        return -1;
-    }
-    GET_METHOD_ID(beginSendObject, clazz, "(Ljava/lang/String;III)I");
-    GET_METHOD_ID(endSendObject, clazz, "(IZ)V");
-    GET_METHOD_ID(rescanFile, clazz, "(Ljava/lang/String;II)V");
-    GET_METHOD_ID(getObjectList, clazz, "(III)[I");
-    GET_METHOD_ID(getNumObjects, clazz, "(III)I");
-    GET_METHOD_ID(getSupportedPlaybackFormats, clazz, "()[I");
-    GET_METHOD_ID(getSupportedCaptureFormats, clazz, "()[I");
-    GET_METHOD_ID(getSupportedObjectProperties, clazz, "(I)[I");
-    GET_METHOD_ID(getSupportedDeviceProperties, clazz, "()[I");
-    GET_METHOD_ID(setObjectProperty, clazz, "(IIJLjava/lang/String;)I");
-    GET_METHOD_ID(getDeviceProperty, clazz, "(I[J[C)I");
-    GET_METHOD_ID(setDeviceProperty, clazz, "(IJLjava/lang/String;)I");
-    GET_METHOD_ID(getObjectPropertyList, clazz, "(IIIII)Landroid/mtp/MtpPropertyList;");
-    GET_METHOD_ID(getObjectInfo, clazz, "(I[I[C[J)Z");
-    GET_METHOD_ID(getObjectFilePath, clazz, "(I[C[J)I");
-    GET_METHOD_ID(openFilePath, clazz, "(Ljava/lang/String;Z)I");
-    GET_METHOD_ID(getThumbnailInfo, clazz, "(I[J)Z");
-    GET_METHOD_ID(getThumbnailData, clazz, "(I)[B");
-    GET_METHOD_ID(beginDeleteObject, clazz, "(I)I");
-    GET_METHOD_ID(endDeleteObject, clazz, "(IZ)V");
-    GET_METHOD_ID(beginMoveObject, clazz, "(III)I");
-    GET_METHOD_ID(endMoveObject, clazz, "(IIIIIZ)V");
-    GET_METHOD_ID(beginCopyObject, clazz, "(III)I");
-    GET_METHOD_ID(endCopyObject, clazz, "(IZ)V");
-    GET_METHOD_ID(getObjectReferences, clazz, "(I)[I");
-    GET_METHOD_ID(setObjectReferences, clazz, "(I[I)I");
-
-    field_context = env->GetFieldID(clazz, "mNativeContext", "J");
-    if (field_context == NULL) {
-        ALOGE("Can't find MtpDatabase.mNativeContext");
-        return -1;
-    }
-
-    clazz = env->FindClass("android/mtp/MtpPropertyList");
-    if (clazz == NULL) {
-        ALOGE("Can't find android/mtp/MtpPropertyList");
-        return -1;
-    }
-    GET_METHOD_ID(getCode, clazz, "()I");
-    GET_METHOD_ID(getCount, clazz, "()I");
-    GET_METHOD_ID(getObjectHandles, clazz, "()[I");
-    GET_METHOD_ID(getPropertyCodes, clazz, "()[I");
-    GET_METHOD_ID(getDataTypes, clazz, "()[I");
-    GET_METHOD_ID(getLongValues, clazz, "()[J");
-    GET_METHOD_ID(getStringValues, clazz, "()[Ljava/lang/String;");
-
     if (AndroidRuntime::registerNativeMethods(env,
                 "android/mtp/MtpDatabase", gMtpDatabaseMethods, NELEM(gMtpDatabaseMethods)))
         return -1;
diff --git a/media/jni/android_mtp_MtpDevice.cpp b/media/jni/android_mtp_MtpDevice.cpp
index 060eaf9ccad4..3d2b00fec26c 100644
--- a/media/jni/android_mtp_MtpDevice.cpp
+++ b/media/jni/android_mtp_MtpDevice.cpp
@@ -34,6 +34,7 @@
 
 #include "android_runtime/AndroidRuntime.h"
 #include "android_runtime/Log.h"
+#include "core_jni_helpers.h"
 #include "nativehelper/ScopedLocalRef.h"
 #include "private/android_filesystem_config.h"
 
@@ -107,6 +108,95 @@ static jfieldID field_event_parameter1;
 static jfieldID field_event_parameter2;
 static jfieldID field_event_parameter3;
 
+// Initializer for  the jclasses, jfieldIDs and jmethodIDs declared above. This method must be
+// invoked before using these static fields for JNI accesses.
+static void initializeJavaIDs(JNIEnv* env) {
+    static std::once_flag sJniInitialized;
+
+    std::call_once(sJniInitialized, [](JNIEnv* env) {
+        clazz_deviceInfo =
+            (jclass)env->NewGlobalRef(FindClassOrDie(env, "android/mtp/MtpDeviceInfo"));
+        constructor_deviceInfo = GetMethodIDOrDie(env, clazz_deviceInfo, "<init>", "()V");
+        field_deviceInfo_manufacturer =
+            GetFieldIDOrDie(env, clazz_deviceInfo, "mManufacturer", "Ljava/lang/String;");
+        field_deviceInfo_model =
+            GetFieldIDOrDie(env, clazz_deviceInfo, "mModel", "Ljava/lang/String;");
+        field_deviceInfo_version =
+            GetFieldIDOrDie(env, clazz_deviceInfo, "mVersion", "Ljava/lang/String;");
+        field_deviceInfo_serialNumber =
+            GetFieldIDOrDie(env, clazz_deviceInfo, "mSerialNumber", "Ljava/lang/String;");
+        field_deviceInfo_operationsSupported =
+            GetFieldIDOrDie(env, clazz_deviceInfo, "mOperationsSupported", "[I");
+        field_deviceInfo_eventsSupported =
+            GetFieldIDOrDie(env, clazz_deviceInfo, "mEventsSupported", "[I");
+
+        clazz_storageInfo =
+            (jclass)env->NewGlobalRef(FindClassOrDie(env, "android/mtp/MtpStorageInfo"));
+        constructor_storageInfo = GetMethodIDOrDie(env, clazz_storageInfo, "<init>", "()V");
+        field_storageInfo_storageId = GetFieldIDOrDie(env, clazz_storageInfo, "mStorageId", "I");
+        field_storageInfo_maxCapacity =
+            GetFieldIDOrDie(env, clazz_storageInfo, "mMaxCapacity", "J");
+        field_storageInfo_freeSpace =
+            GetFieldIDOrDie(env, clazz_storageInfo, "mFreeSpace", "J");
+        field_storageInfo_description =
+            GetFieldIDOrDie(env, clazz_storageInfo, "mDescription", "Ljava/lang/String;");
+        field_storageInfo_volumeIdentifier =
+            GetFieldIDOrDie(env, clazz_storageInfo, "mVolumeIdentifier", "Ljava/lang/String;");
+
+        clazz_objectInfo =
+            (jclass)env->NewGlobalRef(FindClassOrDie(env, "android/mtp/MtpObjectInfo"));
+        constructor_objectInfo = GetMethodIDOrDie(env, clazz_objectInfo, "<init>", "()V");
+        field_objectInfo_handle = GetFieldIDOrDie(env, clazz_objectInfo, "mHandle", "I");
+        field_objectInfo_storageId = GetFieldIDOrDie(env, clazz_objectInfo, "mStorageId", "I");
+        field_objectInfo_format = GetFieldIDOrDie(env, clazz_objectInfo, "mFormat", "I");
+        field_objectInfo_protectionStatus =
+            GetFieldIDOrDie(env, clazz_objectInfo, "mProtectionStatus", "I");
+        field_objectInfo_compressedSize =
+            GetFieldIDOrDie(env, clazz_objectInfo, "mCompressedSize", "I");
+        field_objectInfo_thumbFormat = GetFieldIDOrDie(env, clazz_objectInfo, "mThumbFormat", "I");
+        field_objectInfo_thumbCompressedSize =
+            GetFieldIDOrDie(env, clazz_objectInfo, "mThumbCompressedSize", "I");
+        field_objectInfo_thumbPixWidth =
+            GetFieldIDOrDie(env, clazz_objectInfo, "mThumbPixWidth", "I");
+        field_objectInfo_thumbPixHeight =
+            GetFieldIDOrDie(env, clazz_objectInfo, "mThumbPixHeight", "I");
+        field_objectInfo_imagePixWidth =
+            GetFieldIDOrDie(env, clazz_objectInfo, "mImagePixWidth", "I");
+        field_objectInfo_imagePixHeight =
+            GetFieldIDOrDie(env, clazz_objectInfo, "mImagePixHeight", "I");
+        field_objectInfo_imagePixDepth =
+                GetFieldIDOrDie(env, clazz_objectInfo, "mImagePixDepth", "I");
+        field_objectInfo_parent = GetFieldIDOrDie(env, clazz_objectInfo, "mParent", "I");
+        field_objectInfo_associationType =
+                GetFieldIDOrDie(env, clazz_objectInfo, "mAssociationType", "I");
+        field_objectInfo_associationDesc =
+                GetFieldIDOrDie(env, clazz_objectInfo, "mAssociationDesc", "I");
+        field_objectInfo_sequenceNumber =
+                GetFieldIDOrDie(env, clazz_objectInfo, "mSequenceNumber", "I");
+        field_objectInfo_name =
+                GetFieldIDOrDie(env, clazz_objectInfo, "mName", "Ljava/lang/String;");
+        field_objectInfo_dateCreated = GetFieldIDOrDie(env, clazz_objectInfo, "mDateCreated", "J");
+        field_objectInfo_dateModified =
+                GetFieldIDOrDie(env, clazz_objectInfo, "mDateModified", "J");
+        field_objectInfo_keywords =
+                GetFieldIDOrDie(env, clazz_objectInfo, "mKeywords", "Ljava/lang/String;");
+
+        clazz_event = (jclass)env->NewGlobalRef(FindClassOrDie(env, "android/mtp/MtpEvent"));
+        constructor_event = GetMethodIDOrDie(env, clazz_event, "<init>", "()V");
+        field_event_eventCode = GetFieldIDOrDie(env, clazz_event, "mEventCode", "I");
+        field_event_parameter1 = GetFieldIDOrDie(env, clazz_event, "mParameter1", "I");
+        field_event_parameter2 = GetFieldIDOrDie(env, clazz_event, "mParameter2", "I");
+        field_event_parameter3 = GetFieldIDOrDie(env, clazz_event, "mParameter3", "I");
+
+        const jclass clazz = FindClassOrDie(env, "android/mtp/MtpDevice");
+        field_context = GetFieldIDOrDie(env, clazz, "mNativeContext", "J");
+
+        clazz_io_exception = (jclass)env->NewGlobalRef(FindClassOrDie(env, "java/io/IOException"));
+        clazz_operation_canceled_exception =
+            (jclass)env->NewGlobalRef(FindClassOrDie(env, "android/os/OperationCanceledException"));
+    }, env);
+}
+
 class JavaArrayWriter {
 public:
     JavaArrayWriter(JNIEnv* env, jbyteArray array) :
@@ -132,6 +222,11 @@ private:
 
 MtpDevice* get_device_from_object(JNIEnv* env, jobject javaDevice)
 {
+    // get_device_from_object() is called by the majority of JNI methods in this file. Call
+    // `initializeJavaIDs()` here to ensure JNI methodID's, fieldIDs and classes are initialized
+    // before use.
+    initializeJavaIDs(env);
+
     return (MtpDevice*)env->GetLongField(javaDevice, field_context);
 }
 
@@ -200,6 +295,8 @@ android_mtp_MtpDevice_open(JNIEnv *env, jobject thiz, jstring deviceName, jint f
     MtpDevice* device = MtpDevice::open(deviceNameStr, fd);
     env->ReleaseStringUTFChars(deviceName, deviceNameStr);
 
+    // The jfieldID `field_context` needs to be initialized before use below.
+    initializeJavaIDs(env);
     if (device)
         env->SetLongField(thiz, field_context,  (jlong)device);
     return (jboolean)(device != NULL);
@@ -781,256 +878,7 @@ static const JNINativeMethod gMethods[] = {
 
 int register_android_mtp_MtpDevice(JNIEnv *env)
 {
-    jclass clazz;
-
     ALOGD("register_android_mtp_MtpDevice\n");
-
-    clazz = env->FindClass("android/mtp/MtpDeviceInfo");
-    if (clazz == NULL) {
-        ALOGE("Can't find android/mtp/MtpDeviceInfo");
-        return -1;
-    }
-    constructor_deviceInfo = env->GetMethodID(clazz, "<init>", "()V");
-    if (constructor_deviceInfo == NULL) {
-        ALOGE("Can't find android/mtp/MtpDeviceInfo constructor");
-        return -1;
-    }
-    field_deviceInfo_manufacturer = env->GetFieldID(clazz, "mManufacturer", "Ljava/lang/String;");
-    if (field_deviceInfo_manufacturer == NULL) {
-        ALOGE("Can't find MtpDeviceInfo.mManufacturer");
-        return -1;
-    }
-    field_deviceInfo_model = env->GetFieldID(clazz, "mModel", "Ljava/lang/String;");
-    if (field_deviceInfo_model == NULL) {
-        ALOGE("Can't find MtpDeviceInfo.mModel");
-        return -1;
-    }
-    field_deviceInfo_version = env->GetFieldID(clazz, "mVersion", "Ljava/lang/String;");
-    if (field_deviceInfo_version == NULL) {
-        ALOGE("Can't find MtpDeviceInfo.mVersion");
-        return -1;
-    }
-    field_deviceInfo_serialNumber = env->GetFieldID(clazz, "mSerialNumber", "Ljava/lang/String;");
-    if (field_deviceInfo_serialNumber == NULL) {
-        ALOGE("Can't find MtpDeviceInfo.mSerialNumber");
-        return -1;
-    }
-    field_deviceInfo_operationsSupported = env->GetFieldID(clazz, "mOperationsSupported", "[I");
-    if (field_deviceInfo_operationsSupported == NULL) {
-        ALOGE("Can't find MtpDeviceInfo.mOperationsSupported");
-        return -1;
-    }
-    field_deviceInfo_eventsSupported = env->GetFieldID(clazz, "mEventsSupported", "[I");
-    if (field_deviceInfo_eventsSupported == NULL) {
-        ALOGE("Can't find MtpDeviceInfo.mEventsSupported");
-        return -1;
-    }
-    clazz_deviceInfo = (jclass)env->NewGlobalRef(clazz);
-
-    clazz = env->FindClass("android/mtp/MtpStorageInfo");
-    if (clazz == NULL) {
-        ALOGE("Can't find android/mtp/MtpStorageInfo");
-        return -1;
-    }
-    constructor_storageInfo = env->GetMethodID(clazz, "<init>", "()V");
-    if (constructor_storageInfo == NULL) {
-        ALOGE("Can't find android/mtp/MtpStorageInfo constructor");
-        return -1;
-    }
-    field_storageInfo_storageId = env->GetFieldID(clazz, "mStorageId", "I");
-    if (field_storageInfo_storageId == NULL) {
-        ALOGE("Can't find MtpStorageInfo.mStorageId");
-        return -1;
-    }
-    field_storageInfo_maxCapacity = env->GetFieldID(clazz, "mMaxCapacity", "J");
-    if (field_storageInfo_maxCapacity == NULL) {
-        ALOGE("Can't find MtpStorageInfo.mMaxCapacity");
-        return -1;
-    }
-    field_storageInfo_freeSpace = env->GetFieldID(clazz, "mFreeSpace", "J");
-    if (field_storageInfo_freeSpace == NULL) {
-        ALOGE("Can't find MtpStorageInfo.mFreeSpace");
-        return -1;
-    }
-    field_storageInfo_description = env->GetFieldID(clazz, "mDescription", "Ljava/lang/String;");
-    if (field_storageInfo_description == NULL) {
-        ALOGE("Can't find MtpStorageInfo.mDescription");
-        return -1;
-    }
-    field_storageInfo_volumeIdentifier = env->GetFieldID(clazz, "mVolumeIdentifier", "Ljava/lang/String;");
-    if (field_storageInfo_volumeIdentifier == NULL) {
-        ALOGE("Can't find MtpStorageInfo.mVolumeIdentifier");
-        return -1;
-    }
-    clazz_storageInfo = (jclass)env->NewGlobalRef(clazz);
-
-    clazz = env->FindClass("android/mtp/MtpObjectInfo");
-    if (clazz == NULL) {
-        ALOGE("Can't find android/mtp/MtpObjectInfo");
-        return -1;
-    }
-    constructor_objectInfo = env->GetMethodID(clazz, "<init>", "()V");
-    if (constructor_objectInfo == NULL) {
-        ALOGE("Can't find android/mtp/MtpObjectInfo constructor");
-        return -1;
-    }
-    field_objectInfo_handle = env->GetFieldID(clazz, "mHandle", "I");
-    if (field_objectInfo_handle == NULL) {
-        ALOGE("Can't find MtpObjectInfo.mHandle");
-        return -1;
-    }
-    field_objectInfo_storageId = env->GetFieldID(clazz, "mStorageId", "I");
-    if (field_objectInfo_storageId == NULL) {
-        ALOGE("Can't find MtpObjectInfo.mStorageId");
-        return -1;
-    }
-    field_objectInfo_format = env->GetFieldID(clazz, "mFormat", "I");
-    if (field_objectInfo_format == NULL) {
-        ALOGE("Can't find MtpObjectInfo.mFormat");
-        return -1;
-    }
-    field_objectInfo_protectionStatus = env->GetFieldID(clazz, "mProtectionStatus", "I");
-    if (field_objectInfo_protectionStatus == NULL) {
-        ALOGE("Can't find MtpObjectInfo.mProtectionStatus");
-        return -1;
-    }
-    field_objectInfo_compressedSize = env->GetFieldID(clazz, "mCompressedSize", "I");
-    if (field_objectInfo_compressedSize == NULL) {
-        ALOGE("Can't find MtpObjectInfo.mCompressedSize");
-        return -1;
-    }
-    field_objectInfo_thumbFormat = env->GetFieldID(clazz, "mThumbFormat", "I");
-    if (field_objectInfo_thumbFormat == NULL) {
-        ALOGE("Can't find MtpObjectInfo.mThumbFormat");
-        return -1;
-    }
-    field_objectInfo_thumbCompressedSize = env->GetFieldID(clazz, "mThumbCompressedSize", "I");
-    if (field_objectInfo_thumbCompressedSize == NULL) {
-        ALOGE("Can't find MtpObjectInfo.mThumbCompressedSize");
-        return -1;
-    }
-    field_objectInfo_thumbPixWidth = env->GetFieldID(clazz, "mThumbPixWidth", "I");
-    if (field_objectInfo_thumbPixWidth == NULL) {
-        ALOGE("Can't find MtpObjectInfo.mThumbPixWidth");
-        return -1;
-    }
-    field_objectInfo_thumbPixHeight = env->GetFieldID(clazz, "mThumbPixHeight", "I");
-    if (field_objectInfo_thumbPixHeight == NULL) {
-        ALOGE("Can't find MtpObjectInfo.mThumbPixHeight");
-        return -1;
-    }
-    field_objectInfo_imagePixWidth = env->GetFieldID(clazz, "mImagePixWidth", "I");
-    if (field_objectInfo_imagePixWidth == NULL) {
-        ALOGE("Can't find MtpObjectInfo.mImagePixWidth");
-        return -1;
-    }
-    field_objectInfo_imagePixHeight = env->GetFieldID(clazz, "mImagePixHeight", "I");
-    if (field_objectInfo_imagePixHeight == NULL) {
-        ALOGE("Can't find MtpObjectInfo.mImagePixHeight");
-        return -1;
-    }
-    field_objectInfo_imagePixDepth = env->GetFieldID(clazz, "mImagePixDepth", "I");
-    if (field_objectInfo_imagePixDepth == NULL) {
-        ALOGE("Can't find MtpObjectInfo.mImagePixDepth");
-        return -1;
-    }
-    field_objectInfo_parent = env->GetFieldID(clazz, "mParent", "I");
-    if (field_objectInfo_parent == NULL) {
-        ALOGE("Can't find MtpObjectInfo.mParent");
-        return -1;
-    }
-    field_objectInfo_associationType = env->GetFieldID(clazz, "mAssociationType", "I");
-    if (field_objectInfo_associationType == NULL) {
-        ALOGE("Can't find MtpObjectInfo.mAssociationType");
-        return -1;
-    }
-    field_objectInfo_associationDesc = env->GetFieldID(clazz, "mAssociationDesc", "I");
-    if (field_objectInfo_associationDesc == NULL) {
-        ALOGE("Can't find MtpObjectInfo.mAssociationDesc");
-        return -1;
-    }
-    field_objectInfo_sequenceNumber = env->GetFieldID(clazz, "mSequenceNumber", "I");
-    if (field_objectInfo_sequenceNumber == NULL) {
-        ALOGE("Can't find MtpObjectInfo.mSequenceNumber");
-        return -1;
-    }
-    field_objectInfo_name = env->GetFieldID(clazz, "mName", "Ljava/lang/String;");
-    if (field_objectInfo_name == NULL) {
-        ALOGE("Can't find MtpObjectInfo.mName");
-        return -1;
-    }
-    field_objectInfo_dateCreated = env->GetFieldID(clazz, "mDateCreated", "J");
-    if (field_objectInfo_dateCreated == NULL) {
-        ALOGE("Can't find MtpObjectInfo.mDateCreated");
-        return -1;
-    }
-    field_objectInfo_dateModified = env->GetFieldID(clazz, "mDateModified", "J");
-    if (field_objectInfo_dateModified == NULL) {
-        ALOGE("Can't find MtpObjectInfo.mDateModified");
-        return -1;
-    }
-    field_objectInfo_keywords = env->GetFieldID(clazz, "mKeywords", "Ljava/lang/String;");
-    if (field_objectInfo_keywords == NULL) {
-        ALOGE("Can't find MtpObjectInfo.mKeywords");
-        return -1;
-    }
-    clazz_objectInfo = (jclass)env->NewGlobalRef(clazz);
-
-    clazz = env->FindClass("android/mtp/MtpEvent");
-    if (clazz == NULL) {
-        ALOGE("Can't find android/mtp/MtpEvent");
-        return -1;
-    }
-    constructor_event = env->GetMethodID(clazz, "<init>", "()V");
-    if (constructor_event == NULL) {
-        ALOGE("Can't find android/mtp/MtpEvent constructor");
-        return -1;
-    }
-    field_event_eventCode = env->GetFieldID(clazz, "mEventCode", "I");
-    if (field_event_eventCode == NULL) {
-        ALOGE("Can't find MtpObjectInfo.mEventCode");
-        return -1;
-    }
-    field_event_parameter1 = env->GetFieldID(clazz, "mParameter1", "I");
-    if (field_event_parameter1 == NULL) {
-        ALOGE("Can't find MtpObjectInfo.mParameter1");
-        return -1;
-    }
-    field_event_parameter2 = env->GetFieldID(clazz, "mParameter2", "I");
-    if (field_event_parameter2 == NULL) {
-        ALOGE("Can't find MtpObjectInfo.mParameter2");
-        return -1;
-    }
-    field_event_parameter3 = env->GetFieldID(clazz, "mParameter3", "I");
-    if (field_event_parameter3 == NULL) {
-        ALOGE("Can't find MtpObjectInfo.mParameter3");
-        return -1;
-    }
-    clazz_event = (jclass)env->NewGlobalRef(clazz);
-
-    clazz = env->FindClass("android/mtp/MtpDevice");
-    if (clazz == NULL) {
-        ALOGE("Can't find android/mtp/MtpDevice");
-        return -1;
-    }
-    field_context = env->GetFieldID(clazz, "mNativeContext", "J");
-    if (field_context == NULL) {
-        ALOGE("Can't find MtpDevice.mNativeContext");
-        return -1;
-    }
-    clazz = env->FindClass("java/io/IOException");
-    if (clazz == NULL) {
-        ALOGE("Can't find java.io.IOException");
-        return -1;
-    }
-    clazz_io_exception = (jclass)env->NewGlobalRef(clazz);
-    clazz = env->FindClass("android/os/OperationCanceledException");
-    if (clazz == NULL) {
-        ALOGE("Can't find android.os.OperationCanceledException");
-        return -1;
-    }
-    clazz_operation_canceled_exception = (jclass)env->NewGlobalRef(clazz);
-
     return AndroidRuntime::registerNativeMethods(env,
                 "android/mtp/MtpDevice", gMethods, NELEM(gMethods));
 }
diff --git a/media/jni/android_mtp_MtpServer.cpp b/media/jni/android_mtp_MtpServer.cpp
index 8a1ae9252ca3..b4844f79b540 100644
--- a/media/jni/android_mtp_MtpServer.cpp
+++ b/media/jni/android_mtp_MtpServer.cpp
@@ -24,6 +24,7 @@
 #include <fcntl.h>
 #include <utils/threads.h>
 
+#include "core_jni_helpers.h"
 #include "jni.h"
 #include <nativehelper/JNIPlatformHelp.h>
 #include "android_runtime/AndroidRuntime.h"
@@ -34,6 +35,8 @@
 
 using namespace android;
 
+static Mutex sMutex;
+
 // MtpServer fields
 static jfieldID field_MtpServer_nativeContext;
 
@@ -44,7 +47,25 @@ static jfieldID field_MtpStorage_description;
 static jfieldID field_MtpStorage_removable;
 static jfieldID field_MtpStorage_maxFileSize;
 
-static Mutex sMutex;
+// Initializer for the jfieldIDs above. This method must be invoked before accessing MtpServer and
+// MtpStorage fields.
+static void initializeJavaIDs(JNIEnv* env) {
+    static std::once_flag sJniInitialized;
+
+    std::call_once(sJniInitialized, [](JNIEnv *env) {
+        const jclass storage_clazz = FindClassOrDie(env, "android/mtp/MtpStorage");
+        field_MtpStorage_storageId = GetFieldIDOrDie(env, storage_clazz, "mStorageId", "I");
+        field_MtpStorage_path =
+                GetFieldIDOrDie(env, storage_clazz, "mPath", "Ljava/lang/String;");
+        field_MtpStorage_description =
+                GetFieldIDOrDie(env, storage_clazz, "mDescription", "Ljava/lang/String;");
+        field_MtpStorage_removable = GetFieldIDOrDie(env, storage_clazz, "mRemovable", "Z");
+        field_MtpStorage_maxFileSize = GetFieldIDOrDie(env, storage_clazz, "mMaxFileSize", "J");
+
+        const jclass server_clazz = FindClassOrDie(env, "android/mtp/MtpServer");
+        field_MtpServer_nativeContext = GetFieldIDOrDie(env, server_clazz, "mNativeContext", "J");
+    }, env);
+}
 
 // ----------------------------------------------------------------------------
 
@@ -52,6 +73,7 @@ static Mutex sMutex;
 extern IMtpDatabase* getMtpDatabase(JNIEnv *env, jobject database);
 
 static inline MtpServer* getMtpServer(JNIEnv *env, jobject thiz) {
+    initializeJavaIDs(env);
     return (MtpServer*)env->GetLongField(thiz, field_MtpServer_nativeContext);
 }
 
@@ -60,6 +82,8 @@ android_mtp_MtpServer_setup(JNIEnv *env, jobject thiz, jobject javaDatabase, job
         jboolean usePtp, jstring deviceInfoManufacturer, jstring deviceInfoModel,
         jstring deviceInfoDeviceVersion, jstring deviceInfoSerialNumber)
 {
+    initializeJavaIDs(env);
+
     const char *deviceInfoManufacturerStr = env->GetStringUTFChars(deviceInfoManufacturer, NULL);
     const char *deviceInfoModelStr = env->GetStringUTFChars(deviceInfoModel, NULL);
     const char *deviceInfoDeviceVersionStr = env->GetStringUTFChars(deviceInfoDeviceVersion, NULL);
@@ -224,50 +248,6 @@ static const JNINativeMethod gMethods[] = {
 
 int register_android_mtp_MtpServer(JNIEnv *env)
 {
-    jclass clazz;
-
-    clazz = env->FindClass("android/mtp/MtpStorage");
-    if (clazz == NULL) {
-        ALOGE("Can't find android/mtp/MtpStorage");
-        return -1;
-    }
-    field_MtpStorage_storageId = env->GetFieldID(clazz, "mStorageId", "I");
-    if (field_MtpStorage_storageId == NULL) {
-        ALOGE("Can't find MtpStorage.mStorageId");
-        return -1;
-    }
-    field_MtpStorage_path = env->GetFieldID(clazz, "mPath", "Ljava/lang/String;");
-    if (field_MtpStorage_path == NULL) {
-        ALOGE("Can't find MtpStorage.mPath");
-        return -1;
-    }
-    field_MtpStorage_description = env->GetFieldID(clazz, "mDescription", "Ljava/lang/String;");
-    if (field_MtpStorage_description == NULL) {
-        ALOGE("Can't find MtpStorage.mDescription");
-        return -1;
-    }
-    field_MtpStorage_removable = env->GetFieldID(clazz, "mRemovable", "Z");
-    if (field_MtpStorage_removable == NULL) {
-        ALOGE("Can't find MtpStorage.mRemovable");
-        return -1;
-    }
-    field_MtpStorage_maxFileSize = env->GetFieldID(clazz, "mMaxFileSize", "J");
-    if (field_MtpStorage_maxFileSize == NULL) {
-        ALOGE("Can't find MtpStorage.mMaxFileSize");
-        return -1;
-    }
-
-    clazz = env->FindClass("android/mtp/MtpServer");
-    if (clazz == NULL) {
-        ALOGE("Can't find android/mtp/MtpServer");
-        return -1;
-    }
-    field_MtpServer_nativeContext = env->GetFieldID(clazz, "mNativeContext", "J");
-    if (field_MtpServer_nativeContext == NULL) {
-        ALOGE("Can't find MtpServer.mNativeContext");
-        return -1;
-    }
-
     return AndroidRuntime::registerNativeMethods(env,
                 "android/mtp/MtpServer", gMethods, NELEM(gMethods));
 }