lavc: add JNI support

MAINTAINERS

@@ -196,6 +196,7 @@ Codecs:
   interplayvideo.c                      Mike Melanson
   ivi*                                  Kostya Shishkov
   jacosub*                              Clément Bœsch
+  jni*, ffjni*                          Matthieu Bouron
   jpeg2000*                             Nicolas Bertrand
   jpeg_ls.c                             Kostya Shishkov
   jvdec.c                               Peter Ross

configure

@@ -207,6 +207,7 @@ External library support:
   --enable-gnutls          enable gnutls, needed for https support
                            if openssl is not used [no]
   --disable-iconv          disable iconv [autodetect]
+  --enable-jni             enable JNI support [no]
   --enable-ladspa          enable LADSPA audio filtering [no]
   --enable-libass          enable libass subtitles rendering,
                            needed for subtitles and ass filter [no]
@@ -1436,6 +1437,7 @@ EXTERNAL_LIBRARY_LIST="
     gmp
     gnutls
     iconv
+    jni
     ladspa
     libass
     libbluray
@@ -5556,6 +5558,8 @@ enabled decklink          && { check_header DeckLinkAPI.h || die "ERROR: DeckLin
 enabled frei0r            && { check_header frei0r.h || die "ERROR: frei0r.h header not found"; }
 enabled gmp               && require2 gmp gmp.h mpz_export -lgmp
 enabled gnutls            && require_pkg_config gnutls gnutls/gnutls.h gnutls_global_init
+enabled jni               && { [ $target_os = "android" ] && check_header jni.h && enabled pthreads &&
+                               check_lib2 "dlfcn.h" dlopen -ldl; }
 enabled ladspa            && { check_header ladspa.h || die "ERROR: ladspa.h header not found"; }
 enabled libiec61883       && require libiec61883 libiec61883/iec61883.h iec61883_cmp_connect -lraw1394 -lavc1394 -lrom1394 -liec61883
 enabled libass            && require_pkg_config libass ass/ass.h ass_library_init
@@ -6324,6 +6328,7 @@ echo "threading support         ${thread_type-no}"
 echo "safe bitstream reader     ${safe_bitstream_reader-no}"
 echo "SDL support               ${sdl-no}"
 echo "opencl enabled            ${opencl-no}"
+echo "JNI support               ${jni-no}"
 echo "texi2html enabled         ${texi2html-no}"
 echo "perl enabled              ${perl-no}"
 echo "pod2man enabled           ${pod2man-no}"

libavcodec/Makefile

@@ -9,6 +9,7 @@ HEADERS = avcodec.h                                                     \
           d3d11va.h                                                     \
           dirac.h                                                       \
           dxva2.h                                                       \
+          jni.h                                                         \
           qsv.h                                                         \
           vaapi.h                                                       \
           vda.h                                                         \
@@ -30,6 +31,7 @@ OBJS = allcodecs.o                                                      \
        dirac.o                                                          \
        dv_profile.o                                                     \
        imgconvert.o                                                     \
+       jni.o                                                            \
        mathtables.o                                                     \
        options.o                                                        \
        parser.o                                                         \
@@ -79,6 +81,7 @@ OBJS-$(CONFIG_IIRFILTER)               += iirfilter.o
 OBJS-$(CONFIG_IMDCT15)                 += imdct15.o
 OBJS-$(CONFIG_INTRAX8)                 += intrax8.o intrax8dsp.o
 OBJS-$(CONFIG_IVIDSP)                  += ivi_dsp.o
+OBJS-$(CONFIG_JNI)                     += ffjni.o jni.o
 OBJS-$(CONFIG_JPEGTABLES)              += jpegtables.o
 OBJS-$(CONFIG_LIBXVID)                 += libxvid_rc.o
 OBJS-$(CONFIG_LLAUDDSP)                += lossless_audiodsp.o
@@ -936,6 +939,7 @@ SKIPHEADERS                            += %_tablegen.h                  \
 
 SKIPHEADERS-$(CONFIG_D3D11VA)          += d3d11va.h dxva2_internal.h
 SKIPHEADERS-$(CONFIG_DXVA2)            += dxva2.h dxva2_internal.h
+SKIPHEADERS-$(CONFIG_JNI)              += ffjni.h
 SKIPHEADERS-$(CONFIG_LIBSCHROEDINGER)  += libschroedinger.h
 SKIPHEADERS-$(CONFIG_LIBUTVIDEO)       += libutvideo.h
 SKIPHEADERS-$(CONFIG_LIBVPX)           += libvpx.h

libavcodec/ffjni.c

+/*
+ * JNI utility functions
+ *
+ * Copyright (c) 2015-2016 Matthieu Bouron <matthieu.bouron stupeflix.com>
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <dlfcn.h>
+#include <jni.h>
+#include <pthread.h>
+#include <stdlib.h>
+
+#include "libavutil/bprint.h"
+#include "libavutil/log.h"
+
+#include "config.h"
+#include "jni.h"
+#include "ffjni.h"
+
+static JavaVM *java_vm = NULL;
+static pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
+
+/**
+ * Check if JniInvocation has been initialized. Only available on
+ * Android >= 4.4.
+ *
+ * @param log_ctx context used for logging, can be NULL
+ * @return 0 on success, < 0 otherwise
+ */
+static int check_jni_invocation(void *log_ctx)
+{
+    int ret = AVERROR_EXTERNAL;
+    void *handle = NULL;
+    void **jni_invocation = NULL;
+
+    handle = dlopen(NULL, RTLD_LOCAL);
+    if (!handle) {
+        goto done;
+    }
+
+    jni_invocation = (void **)dlsym(handle, "_ZN13JniInvocation15jni_invocation_E");
+    if (!jni_invocation) {
+        av_log(log_ctx, AV_LOG_ERROR, "Could not find JniInvocation::jni_invocation_ symbol\n");
+        goto done;
+    }
+
+    ret = !(jni_invocation != NULL && *jni_invocation != NULL);
+
+done:
+    if (handle) {
+        dlclose(handle);
+    }
+
+    return ret;
+}
+
+/**
+ * Return created Java virtual machine using private JNI_GetCreatedJavaVMs
+ * function from the specified library name.
+ *
+ * @param name library name used for symbol lookups, can be NULL
+ * @param log_ctx context used for logging, can be NULL
+ * @return the current Java virtual machine in use
+ */
+static JavaVM *get_java_vm(const char *name, void *log_ctx)
+{
+    JavaVM *vm = NULL;
+    jsize nb_vm = 0;
+
+    void *handle = NULL;
+    jint (*get_created_java_vms) (JavaVM ** vmBuf, jsize bufLen, jsize *nVMs) = NULL;
+
+    handle = dlopen(name, RTLD_LOCAL);
+    if (!handle) {
+        return NULL;
+    }
+
+    get_created_java_vms = (jint (*)(JavaVM **, jsize, jsize *)) dlsym(handle, "JNI_GetCreatedJavaVMs");
+    if (!get_created_java_vms) {
+        av_log(log_ctx, AV_LOG_ERROR, "Could not find JNI_GetCreatedJavaVMs symbol in library '%s'\n", name);
+        goto done;
+    }
+
+    if (get_created_java_vms(&vm, 1, &nb_vm) != JNI_OK) {
+        av_log(log_ctx, AV_LOG_ERROR, "Could not get created Java virtual machines\n");
+        goto done;
+    }
+
+done:
+    if (handle) {
+        dlclose(handle);
+    }
+
+    return vm;
+}
+
+JNIEnv *ff_jni_attach_env(int *attached, void *log_ctx)
+{
+    int ret = 0;
+    JNIEnv *env = NULL;
+
+    *attached = 0;
+
+    pthread_mutex_lock(&lock);
+    if (java_vm == NULL && (java_vm = av_jni_get_java_vm(log_ctx)) == NULL) {
+
+        av_log(log_ctx, AV_LOG_INFO, "Retrieving current Java virtual machine using Android JniInvocation wrapper\n");
+        if (check_jni_invocation(log_ctx) == 0) {
+            if ((java_vm = get_java_vm(NULL, log_ctx)) != NULL ||
+                (java_vm = get_java_vm("libdvm.so", log_ctx)) != NULL ||
+                (java_vm = get_java_vm("libart.so", log_ctx)) != NULL) {
+                av_log(log_ctx, AV_LOG_INFO, "Found Java virtual machine using Android JniInvocation wrapper\n");
+            }
+        }
+    }
+    pthread_mutex_unlock(&lock);
+
+    if (!java_vm) {
+        av_log(log_ctx, AV_LOG_ERROR, "Could not retrieve a Java virtual machine\n");
+        return NULL;
+    }
+
+    ret = (*java_vm)->GetEnv(java_vm, (void **)&env, JNI_VERSION_1_6);
+    switch(ret) {
+    case JNI_EDETACHED:
+        if ((*java_vm)->AttachCurrentThread(java_vm, &env, NULL) != 0) {
+            av_log(log_ctx, AV_LOG_ERROR, "Failed to attach the JNI environment to the current thread\n");
+            env = NULL;
+        } else {
+            *attached = 1;
+        }
+        break;
+    case JNI_OK:
+        break;
+    case JNI_EVERSION:
+        av_log(log_ctx, AV_LOG_ERROR, "The specified JNI version is not supported\n");
+        break;
+    default:
+        av_log(log_ctx, AV_LOG_ERROR, "Failed to get the JNI environment attached to this thread");
+        break;
+    }
+
+    return env;
+}
+
+int ff_jni_detach_env(void *log_ctx)
+{
+    if (java_vm == NULL) {
+        av_log(log_ctx, AV_LOG_ERROR, "No Java virtual machine has been registered\n");
+        return AVERROR(EINVAL);
+    }
+
+    return (*java_vm)->DetachCurrentThread(java_vm);
+}
+
+char *ff_jni_jstring_to_utf_chars(JNIEnv *env, jstring string, void *log_ctx)
+{
+    char *ret = NULL;
+    const char *utf_chars = NULL;
+
+    jboolean copy = 0;
+
+    if (!string) {
+        return NULL;
+    }
+
+    utf_chars = (*env)->GetStringUTFChars(env, string, &copy);
+    if ((*env)->ExceptionCheck(env)) {
+        (*env)->ExceptionClear(env);
+        av_log(log_ctx, AV_LOG_ERROR, "String.getStringUTFChars() threw an exception\n");
+        return NULL;
+    }
+
+    ret = av_strdup(utf_chars);
+
+    (*env)->ReleaseStringUTFChars(env, string, utf_chars);
+    if ((*env)->ExceptionCheck(env)) {
+        (*env)->ExceptionClear(env);
+        av_log(log_ctx, AV_LOG_ERROR, "String.releaseStringUTFChars() threw an exception\n");
+        return NULL;;
+    }
+
+    return ret;
+}
+
+jstring ff_jni_utf_chars_to_jstring(JNIEnv *env, const char *utf_chars, void *log_ctx)
+{
+    jstring ret;
+
+    ret = (*env)->NewStringUTF(env, utf_chars);
+    if ((*env)->ExceptionCheck(env)) {
+        (*env)->ExceptionClear(env);
+        av_log(log_ctx, AV_LOG_ERROR, "NewStringUTF() threw an exception\n");
+        return NULL;
+    }
+
+    return ret;
+}
+
+int ff_jni_exception_get_summary(JNIEnv *env, jthrowable exception, char **error, void *log_ctx)
+{
+    int ret = 0;
+
+    AVBPrint bp;
+
+    char *name = NULL;
+    char *message = NULL;
+
+    jclass class_class = NULL;
+    jmethodID get_name_id = NULL;
+
+    jclass exception_class = NULL;
+    jmethodID get_message_id = NULL;
+
+    jstring string;
+
+    av_bprint_init(&bp, 0, AV_BPRINT_SIZE_AUTOMATIC);
+
+    exception_class = (*env)->GetObjectClass(env, exception);
+    if ((*env)->ExceptionCheck(env)) {
+        (*env)->ExceptionClear(env);
+        av_log(log_ctx, AV_LOG_ERROR, "Could not find Throwable class\n");
+        ret = AVERROR_EXTERNAL;
+        goto done;
+    }
+
+    class_class = (*env)->GetObjectClass(env, exception_class);
+    if ((*env)->ExceptionCheck(env)) {
+        (*env)->ExceptionClear(env);
+        av_log(log_ctx, AV_LOG_ERROR, "Could not find Throwable class's class\n");
+        ret = AVERROR_EXTERNAL;
+        goto done;
+    }
+
+    get_name_id = (*env)->GetMethodID(env, class_class, "getName", "()Ljava/lang/String;");
+    if ((*env)->ExceptionCheck(env)) {
+        (*env)->ExceptionClear(env);
+        av_log(log_ctx, AV_LOG_ERROR, "Could not find method Class.getName()\n");
+        ret = AVERROR_EXTERNAL;
+        goto done;
+    }
+
+    string = (*env)->CallObjectMethod(env, exception_class, get_name_id);
+    if ((*env)->ExceptionCheck(env)) {
+        (*env)->ExceptionClear(env);
+        av_log(log_ctx, AV_LOG_ERROR, "Class.getName() threw an exception\n");
+        ret = AVERROR_EXTERNAL;
+        goto done;
+    }
+
+    if (string) {
+        name = ff_jni_jstring_to_utf_chars(env, string, log_ctx);
+        (*env)->DeleteLocalRef(env, string);
+        string = NULL;
+    }
+
+    get_message_id = (*env)->GetMethodID(env, exception_class, "getMessage", "()Ljava/lang/String;");
+    if ((*env)->ExceptionCheck(env)) {
+        (*env)->ExceptionClear(env);
+        av_log(log_ctx, AV_LOG_ERROR, "Could not find method java/lang/Throwable.getMessage()\n");
+        ret = AVERROR_EXTERNAL;
+        goto done;
+    }
+
+    string = (*env)->CallObjectMethod(env, exception, get_message_id);
+    if ((*env)->ExceptionCheck(env)) {
+        (*env)->ExceptionClear(env);
+        av_log(log_ctx, AV_LOG_ERROR, "Throwable.getMessage() threw an exception\n");
+        ret = AVERROR_EXTERNAL;
+        goto done;
+    }
+
+    if (string) {
+        message = ff_jni_jstring_to_utf_chars(env, string, log_ctx);
+        (*env)->DeleteLocalRef(env, string);
+        string = NULL;
+    }
+
+    if (name && message) {
+        av_bprintf(&bp, "%s: %s", name, message);
+    } else if (name && !message) {
+        av_bprintf(&bp, "%s occured", name);
+    } else if (!name && message) {
+        av_bprintf(&bp, "Exception: %s", message);
+    } else {
+        av_log(log_ctx, AV_LOG_WARNING, "Could not retreive exception name and message\n");
+        av_bprintf(&bp, "Exception occured");
+    }
+
+    ret = av_bprint_finalize(&bp, error);
+done:
+
+    av_free(name);
+    av_free(message);
+
+    if (class_class) {
+        (*env)->DeleteLocalRef(env, class_class);
+    }
+
+    if (exception_class) {
+        (*env)->DeleteLocalRef(env, exception_class);
+    }
+
+    if (string) {
+        (*env)->DeleteLocalRef(env, string);
+    }
+
+    return ret;
+}
+
+int ff_jni_exception_check(JNIEnv *env, int log, void *log_ctx)
+{
+    int ret;
+
+    jthrowable exception;
+
+    char *message = NULL;
+
+    if (!(*(env))->ExceptionCheck((env))) {
+        return 0;
+    }
+
+    if (!log) {
+        (*(env))->ExceptionClear((env));
+        return -1;
+    }
+
+    exception = (*env)->ExceptionOccurred(env);
+    (*(env))->ExceptionClear((env));
+
+    if ((ret = ff_jni_exception_get_summary(env, exception, &message, log_ctx)) < 0) {
+        (*env)->DeleteLocalRef(env, exception);
+        return ret;
+    }
+
+    (*env)->DeleteLocalRef(env, exception);
+
+    av_log(log_ctx, AV_LOG_ERROR, "%s\n", message);
+    av_free(message);
+
+    return -1;
+}
+
+int ff_jni_init_jfields(JNIEnv *env, void *jfields, const struct FFJniField *jfields_mapping, int global, void *log_ctx)
+{
+    int i, ret = 0;
+    jclass last_clazz = NULL;
+
+    for (i = 0; jfields_mapping[i].name; i++) {
+        int mandatory = jfields_mapping[i].mandatory;
+        enum FFJniFieldType type = jfields_mapping[i].type;
+
+        if (type == FF_JNI_CLASS) {
+            jclass clazz;
+
+            last_clazz = NULL;
+
+            clazz = (*env)->FindClass(env, jfields_mapping[i].name);
+            if ((ret = ff_jni_exception_check(env, mandatory, log_ctx)) < 0 && mandatory) {
+                goto done;
+            }
+
+            last_clazz = *(jclass*)((uint8_t*)jfields + jfields_mapping[i].offset) =
+                    global ? (*env)->NewGlobalRef(env, clazz) : clazz;
+        } else {
+
+            if (!last_clazz) {
+                ret = AVERROR_EXTERNAL;
+                break;
+            }
+
+            switch(type) {
+            case FF_JNI_FIELD: {
+                jfieldID field_id = (*env)->GetFieldID(env, last_clazz, jfields_mapping[i].method, jfields_mapping[i].signature);
+                if ((ret = ff_jni_exception_check(env, mandatory, log_ctx)) < 0 && mandatory) {
+                    goto done;
+                }
+
+                *(jfieldID*)((uint8_t*)jfields + jfields_mapping[i].offset) = field_id;
+                break;
+            }
+            case FF_JNI_STATIC_FIELD: {
+                jfieldID field_id = (*env)->GetStaticFieldID(env, last_clazz, jfields_mapping[i].method, jfields_mapping[i].signature);
+                if ((ret = ff_jni_exception_check(env, mandatory, log_ctx)) < 0 && mandatory) {
+                    goto done;
+                }
+
+                *(jfieldID*)((uint8_t*)jfields + jfields_mapping[i].offset) = field_id;
+                break;
+            }
+            case FF_JNI_METHOD: {
+                jmethodID method_id = (*env)->GetMethodID(env, last_clazz, jfields_mapping[i].method, jfields_mapping[i].signature);
+                if ((ret = ff_jni_exception_check(env, mandatory, log_ctx)) < 0 && mandatory) {
+                    goto done;
+                }
+
+                *(jmethodID*)((uint8_t*)jfields + jfields_mapping[i].offset) = method_id;
+                break;
+            }
+            case FF_JNI_STATIC_METHOD: {
+                jmethodID method_id = (*env)->GetStaticMethodID(env, last_clazz, jfields_mapping[i].method, jfields_mapping[i].signature);
+                if ((ret = ff_jni_exception_check(env, mandatory, log_ctx)) < 0 && mandatory) {
+                    goto done;
+                }
+
+                *(jmethodID*)((uint8_t*)jfields + jfields_mapping[i].offset) = method_id;
+                break;
+            }
+            default:
+                av_log(log_ctx, AV_LOG_ERROR, "Unknown JNI field type\n");
+                ret = AVERROR(EINVAL);
+                goto done;
+            }
+        }
+    }
+
+done:
+    if (ret < 0) {
+        /* reset jfields in case of failure so it does not leak references */
+        ff_jni_reset_jfields(env, jfields, jfields_mapping, global, log_ctx);
+    }
+
+    return ret;
+}
+
+int ff_jni_reset_jfields(JNIEnv *env, void *jfields, const struct FFJniField *jfields_mapping, int global, void *log_ctx)
+{
+    int i;
+
+    for (i = 0; jfields_mapping[i].name; i++) {
+        enum FFJniFieldType type = jfields_mapping[i].type;
+
+        switch(type) {
+        case FF_JNI_CLASS: {
+            jclass clazz = *(jclass*)((uint8_t*)jfields + jfields_mapping[i].offset);
+            if (!clazz)
+                continue;
+
+            if (global) {
+                (*env)->DeleteGlobalRef(env, clazz);
+            } else {
+                (*env)->DeleteLocalRef(env, clazz);
+            }
+
+            *(jclass*)((uint8_t*)jfields + jfields_mapping[i].offset) = NULL;
+            break;
+        }
+        case FF_JNI_FIELD: {
+            *(jfieldID*)((uint8_t*)jfields + jfields_mapping[i].offset) = NULL;
+            break;
+        }
+        case FF_JNI_STATIC_FIELD: {
+            *(jfieldID*)((uint8_t*)jfields + jfields_mapping[i].offset) = NULL;
+            break;
+        }
+        case FF_JNI_METHOD: {
+            *(jmethodID*)((uint8_t*)jfields + jfields_mapping[i].offset) = NULL;
+            break;
+        }
+        case FF_JNI_STATIC_METHOD: {
+            *(jmethodID*)((uint8_t*)jfields + jfields_mapping[i].offset) = NULL;
+            break;
+        }
+        default:
+            av_log(log_ctx, AV_LOG_ERROR, "Unknown JNI field type\n");
+        }
+    }
+
+    return 0;
+}

libavcodec/ffjni.h

+/*
+ * JNI utility functions
+ *
+ * Copyright (c) 2015-2016 Matthieu Bouron <matthieu.bouron stupeflix.com>
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef AVCODEC_FFJNI_H
+#define AVCODEC_FFJNI_H
+
+#include <jni.h>
+
+/*
+ * Attach a JNI environment to the current thread.
+ *
+ * @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
+ * already attached.
+ * @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);
+
+/*
+ * Convert a jstring to its utf characters equivalent.
+ *
+ * @param env JNI environment
+ * @param string Java string to convert
+ * @param log_ctx context used for logging, can be NULL
+ * @return a pointer to an array of unicode characters on success, NULL
+ * otherwise
+ */
+char *ff_jni_jstring_to_utf_chars(JNIEnv *env, jstring string, void *log_ctx);
+
+/*
+ * Convert utf chars to its jstring equivalent.
+ *
+ * @param env JNI environment
+ * @param utf_chars a pointer to an array of unicode characters
+ * @param log_ctx context used for logging, can be NULL
+ * @return a Java string object on success, NULL otherwise
+ */
+jstring ff_jni_utf_chars_to_jstring(JNIEnv *env, const char *utf_chars, void *log_ctx);
+
+/*
+ * Extract the error summary from a jthrowable in the form of "className: errorMessage"
+ *
+ * @param env JNI environment
+ * @param exception exception to get the summary from
+ * @param error address pointing to the error, the value is updated if a
+ * summary can be extracted
+ * @param log_ctx context used for logging, can be NULL
+ * @return 0 on success, < 0 otherwise
+ */
+int ff_jni_exception_get_summary(JNIEnv *env, jthrowable exception, char **error, void *log_ctx);
+
+/*
+ * Check if an exception has occurred,log it using av_log and clear it.
+ *
+ * @param env JNI environment
+ * @param log value used to enable logging if an exception has occurred,
+ * 0 disables logging, != 0 enables logging
+ * @param log_ctx context used for logging, can be NULL
+ */
+int ff_jni_exception_check(JNIEnv *env, int log, void *log_ctx);
+
+/*
+ * Jni field type.
+ */
+enum FFJniFieldType {
+
+    FF_JNI_CLASS,
+    FF_JNI_FIELD,
+    FF_JNI_STATIC_FIELD,
+    FF_JNI_METHOD,
+    FF_JNI_STATIC_METHOD
+
+};
+
+/*
+ * Jni field describing a class, a field or a method to be retrieved using
+ * the ff_jni_init_jfields method.
+ */
+struct FFJniField {
+
+    const char *name;
+    const char *method;
+    const char *signature;
+    enum FFJniFieldType type;
+    int offset;
+    int mandatory;
+
+};
+
+/*
+ * Retrieve class references, field ids and method ids to an arbitrary structure.
+ *
+ * @param env JNI environment
+ * @param jfields a pointer to an arbitrary structure where the different
+ * fields are declared and where the FFJNIField mapping table offsets are
+ * pointing to
+ * @param jfields_mapping null terminated array of FFJNIFields describing
+ * the class/field/method to be retrieved
+ * @param global make the classes references global. It is the caller
+ * responsibility to properly release global references.
+ * @param log_ctx context used for logging, can be NULL
+ * @return 0 on success, < 0 otherwise
+ */
+int ff_jni_init_jfields(JNIEnv *env, void *jfields, const struct FFJniField *jfields_mapping, int global, void *log_ctx);
+
+/*
+ * Delete class references, field ids and method ids of an arbitrary structure.
+ *
+ * @param env JNI environment
+ * @param jfields a pointer to an arbitrary structure where the different
+ * fields are declared and where the FFJNIField mapping table offsets are
+ * pointing to
+ * @param jfields_mapping null terminated array of FFJNIFields describing
+ * the class/field/method to be deleted
+ * @param global threat the classes references as global and delete them
+ * accordingly
+ * @param log_ctx context used for logging, can be NULL
+ * @return 0 on success, < 0 otherwise
+ */
+int ff_jni_reset_jfields(JNIEnv *env, void *jfields, const struct FFJniField *jfields_mapping, int global, void *log_ctx);
+
+#endif /* AVCODEC_FFJNI_H */

libavcodec/jni.c

+/*
+ * JNI public API functions
+ *
+ * Copyright (c) 2015-2016 Matthieu Bouron <matthieu.bouron stupeflix.com>
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <stdlib.h>
+
+#include "config.h"
+#include "jni.h"
+
+#if CONFIG_JNI
+
+#include <errno.h>
+#include <jni.h>
+#include <pthread.h>
+
+#include "libavutil/log.h"
+#include "libavutil/error.h"
+#include "ffjni.h"
+
+void *java_vm;
+pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
+
+int av_jni_set_java_vm(void *vm, void *log_ctx)
+{
+    int ret = 0;
+
+    pthread_mutex_lock(&lock);
+    if (java_vm == NULL) {
+        java_vm = vm;
+    } else if (java_vm != vm) {
+        ret = AVERROR(EINVAL);
+        av_log(log_ctx, AV_LOG_ERROR, "A Java virtual machine has already been set");
+    }
+    pthread_mutex_unlock(&lock);
+
+    return ret;
+}
+
+void *av_jni_get_java_vm(void *log_ctx)
+{
+    void *vm;
+
+    pthread_mutex_lock(&lock);
+    vm = java_vm;
+    pthread_mutex_unlock(&lock);
+
+    return vm;
+}
+
+#else
+
+int av_jni_set_java_vm(void *vm, void *log_ctx)
+{
+    return 0;
+}
+
+void *av_jni_get_java_vm(void *log_ctx)
+{
+    return NULL;
+}
+
+#endif

libavcodec/jni.h

+/*
+ * JNI public API functions
+ *
+ * Copyright (c) 2015-2016 Matthieu Bouron <matthieu.bouron stupeflix.com>
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef AVCODEC_JNI_H
+#define AVCODEC_JNI_H
+
+/*
+ * Manually set a Java virtual machine which will be used to retrieve the JNI
+ * environment. Once a Java VM is set it cannot be changed afterwards, meaning
+ * you can call multiple times av_jni_set_java_vm with the same Java VM pointer
+ * however it will error out if you try to set a different Java VM.
+ *
+ * @param vm Java virtual machine
+ * @param log_ctx context used for logging, can be NULL
+ * @return 0 on success, < 0 otherwise
+ */
+int av_jni_set_java_vm(void *vm, void *log_ctx);
+
+/*
+ * Get the Java virtual machine which has been set with av_jni_set_java_vm.
+ *
+ * @param vm Java virtual machine
+ * @return a pointer to the Java virtual machine
+ */
+void *av_jni_get_java_vm(void *log_ctx);
+
+#endif /* AVCODEC_JNI_H */