blob: 4cf1aa5e8eaa15817235d4dec8dd6976b3f3dce2 [file] [log] [blame]
* Copyright 2018 The WebRTC project authors. All Rights Reserved.
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
#include "sdk/android/src/jni/jvm.h"
#include <asm/unistd.h>
#include <pthread.h>
#include <sys/prctl.h>
#include <sys/syscall.h>
#include <unistd.h>
#include <string>
#include "rtc_base/checks.h"
namespace webrtc {
namespace jni {
static JavaVM* g_jvm = nullptr;
static pthread_once_t g_jni_ptr_once = PTHREAD_ONCE_INIT;
// Key for per-thread JNIEnv* data. Non-NULL in threads attached to `g_jvm` by
// AttachCurrentThreadIfNeeded(), NULL in unattached threads and threads that
// were attached by the JVM because of a Java->native call.
static pthread_key_t g_jni_ptr;
JavaVM* GetJVM() {
RTC_CHECK(g_jvm) << "JNI_OnLoad failed to run?";
return g_jvm;
// Return a |JNIEnv*| usable on this thread or NULL if this thread is detached.
JNIEnv* GetEnv() {
void* env = nullptr;
jint status = g_jvm->GetEnv(&env, JNI_VERSION_1_6);
RTC_CHECK(((env != nullptr) && (status == JNI_OK)) ||
((env == nullptr) && (status == JNI_EDETACHED)))
<< "Unexpected GetEnv return: " << status << ":" << env;
return reinterpret_cast<JNIEnv*>(env);
static void ThreadDestructor(void* prev_jni_ptr) {
// This function only runs on threads where `g_jni_ptr` is non-NULL, meaning
// we were responsible for originally attaching the thread, so are responsible
// for detaching it now. However, because some JVM implementations (notably
// Oracle's also use the pthread_key_create mechanism,
// the JVMs accounting info for this thread may already be wiped out by the
// time this is called. Thus it may appear we are already detached even though
// it was our responsibility to detach! Oh well.
if (!GetEnv())
RTC_CHECK(GetEnv() == prev_jni_ptr)
<< "Detaching from another thread: " << prev_jni_ptr << ":" << GetEnv();
jint status = g_jvm->DetachCurrentThread();
RTC_CHECK(status == JNI_OK) << "Failed to detach thread: " << status;
RTC_CHECK(!GetEnv()) << "Detaching was a successful no-op???";
static void CreateJNIPtrKey() {
RTC_CHECK(!pthread_key_create(&g_jni_ptr, &ThreadDestructor))
<< "pthread_key_create";
jint InitGlobalJniVariables(JavaVM* jvm) {
RTC_CHECK(!g_jvm) << "InitGlobalJniVariables!";
g_jvm = jvm;
RTC_CHECK(g_jvm) << "InitGlobalJniVariables handed NULL?";
RTC_CHECK(!pthread_once(&g_jni_ptr_once, &CreateJNIPtrKey)) << "pthread_once";
JNIEnv* jni = nullptr;
if (jvm->GetEnv(reinterpret_cast<void**>(&jni), JNI_VERSION_1_6) != JNI_OK)
return -1;
return JNI_VERSION_1_6;
// Return thread ID as a string.
static std::string GetThreadId() {
char buf[21]; // Big enough to hold a kuint64max plus terminating NULL.
RTC_CHECK_LT(snprintf(buf, sizeof(buf), "%ld",
<< "Thread id is bigger than uint64??";
return std::string(buf);
// Return the current thread's name.
static std::string GetThreadName() {
char name[17] = {0};
if (prctl(PR_GET_NAME, name) != 0)
return std::string("<noname>");
return std::string(name);
// Return a |JNIEnv*| usable on this thread. Attaches to `g_jvm` if necessary.
JNIEnv* AttachCurrentThreadIfNeeded() {
JNIEnv* jni = GetEnv();
if (jni)
return jni;
<< "TLS has a JNIEnv* but not attached?";
std::string name(GetThreadName() + " - " + GetThreadId());
JavaVMAttachArgs args;
args.version = JNI_VERSION_1_6; = &name[0]; = nullptr;
// Deal with difference in signatures between Oracle's jni.h and Android's.
#ifdef _JAVASOFT_JNI_H_ // Oracle's jni.h violates the JNI spec!
void* env = nullptr;
JNIEnv* env = nullptr;
RTC_CHECK(!g_jvm->AttachCurrentThread(&env, &args))
<< "Failed to attach thread";
RTC_CHECK(env) << "AttachCurrentThread handed back NULL!";
jni = reinterpret_cast<JNIEnv*>(env);
RTC_CHECK(!pthread_setspecific(g_jni_ptr, jni)) << "pthread_setspecific";
return jni;
} // namespace jni
} // namespace webrtc