Media进程是init.rc进程解析的
service media /system/bin/mediaserver
class main
user media
group audio camera inet net_bt net_bt_admin net_bw_acct drmrpc mediadrm
ioprio rt 4
实际是mediaserver的main方法
MediaServer的main方法
android-6.0.1_r1\frameworks\av\media\mediaserver\main_mediaserver.cpp
int main(int argc __unused, char** argv)
{
//1、获取ProcessState实例
sp<ProcessState> proc(ProcessState::self());
//2、得到IServiceManager
sp<IServiceManager> sm = defaultServiceManager();
ALOGI("ServiceManager: %p", sm.get());
AudioFlinger::instantiate();
// 3、注册MediaPlayerService
MediaPlayerService::instantiate();
ResourceManagerService::instantiate();
CameraService::instantiate();
AudioPolicyService::instantiate();
SoundTriggerHwService::instantiate();
RadioService::instantiate();
registerExtensions();
//4、启动binder线程池
ProcessState::self()->startThreadPool();
//5、当前线程加入到线程池
IPCThreadState::self()->joinThreadPool();
}
1、获取进程唯一ProcessState
sp<ProcessState> ProcessState::self()
{
Mutex::Autolock _l(gProcessMutex);
//实际是通过单例获取ProcessState
if (gProcess != NULL) {
return gProcess;
}
gProcess = new ProcessState;
return gProcess;
}
ProcessState::ProcessState()
: mDriverFD(open_driver())//open_driver打开驱动
, mVMStart(MAP_FAILED)
, mThreadCountLock(PTHREAD_MUTEX_INITIALIZER)
, mThreadCountDecrement(PTHREAD_COND_INITIALIZER)
, mExecutingThreadsCount(0)
, mMaxThreads(DEFAULT_MAX_BINDER_THREADS)
, mManagesContexts(false)
, mBinderContextCheckFunc(NULL)
, mBinderContextUserData(NULL)
, mThreadPoolStarted(false)
, mThreadPoolSeq(1)
{
if (mDriverFD >= 0) {
#if !defined(HAVE_WIN32_IPC)
// mmap内存映射
mVMStart = mmap(0, BINDER_VM_SIZE, PROT_READ, MAP_PRIVATE | MAP_NORESERVE, mDriverFD, 0);
if (mVMStart == MAP_FAILED) {
// *sigh*
ALOGE("Using /dev/binder failed: unable to mmap transaction memory.\n");
close(mDriverFD);
mDriverFD = -1;
}
#else
mDriverFD = -1;
#endif
}
}
打开驱动
static int open_driver()
{
//打开binder驱动并返回文件操作符
int fd = open("/dev/binder", O_RDWR);
if (fd >= 0) {
..............
size_t maxThreads = DEFAULT_MAX_BINDER_THREADS;
//设置binder支持的最大线程数是15
result = ioctl(fd, BINDER_SET_MAX_THREADS, &maxThreads);
if (result == -1) {
ALOGE("Binder ioctl to set max threads failed: %s", strerror(errno));
}
} else {
ALOGW("Opening '/dev/binder' failed: %s\n", strerror(errno));
}
return fd;
}
//最大线程数15
#define DEFAULT_MAX_BINDER_THREADS 15
ProcessState主要做了两件事情:
1、打开binder驱动（/dev/binder）并设置最大线程数是15
2、通过mmap为binder分配一块虚拟内存地址空间，实现内存映射的目的
2、得到IServiceManager
sp<IServiceManager> defaultServiceManager()
{
//如果不为空直接返回
if (gDefaultServiceManager != NULL) return gDefaultServiceManager;
{
AutoMutex _l(gDefaultServiceManagerLock);
while (gDefaultServiceManager == NULL) {
gDefaultServiceManager = interface_cast<IServiceManager>(
ProcessState::self()->getContextObject(NULL));
if (gDefaultServiceManager == NULL)
sleep(1);
}
}
return gDefaultServiceManager;
}
sp<IBinder> ProcessState::getContextObject(const sp<IBinder>& /*caller*/)
{
return getStrongProxyForHandle(0);
}
sp<IBinder> ProcessState::getStrongProxyForHandle(int32_t handle)
{
sp<IBinder> result;
AutoMutex _l(mLock);
handle_entry* e = lookupHandleLocked(handle);
if (e != NULL) {
//刚开始e->binder为空
IBinder* b = e->binder;
if (b == NULL || !e->refs->attemptIncWeak(this)) {
if (handle == 0) {
Parcel data;
status_t status = IPCThreadState::self()->transact(
0, IBinder::PING_TRANSACTION, data, NULL, 0);
if (status == DEAD_OBJECT)
return NULL;
}
//new了一个BpBinder,handle=0
b = new BpBinder(handle);
e->binder = b;
if (b) e->refs = b->getWeakRefs();
result = b;
} else {
result.force_set(b);
e->refs->decWeak(this);
}
}
return result;
}
此时defaultServiceManager变成以下
sp<IServiceManager> defaultServiceManager()
{
//如果不为空直接返回
if (gDefaultServiceManager != NULL) return gDefaultServiceManager;
{
gDefaultServiceManager = interface_cast<IServiceManager>(
new BpBinder(0);
}
return gDefaultServiceManager;
}
template<typename INTERFACE>
inline sp<INTERFACE> interface_cast(const sp<IBinder>& obj)
{
//INTERFACE实际是IServiceManager
return INTERFACE::asInterface(obj);
}
在IServicemanager中找asInterface没有找到，但是我们可以看到IServiemanager.h中实际继承的是IInterface
class IServiceManager : public IInterface
{
public:
DECLARE_META_INTERFACE(ServiceManager);
};
#define IMPLEMENT_META_INTERFACE(INTERFACE, NAME) \
const android::String16 I##INTERFACE::descriptor(NAME); \
const android::String16& \
I##INTERFACE::getInterfaceDescriptor() const { \
return I##INTERFACE::descriptor; \
} \
android::sp<I##INTERFACE> I##INTERFACE::asInterface( \
const android::sp<android::IBinder>& obj) \
{ \
android::sp<I##INTERFACE> intr; \
if (obj != NULL) { \
intr = static_cast<I##INTERFACE*>( \
obj->queryLocalInterface( \
I##INTERFACE::descriptor).get()); \
if (intr == NULL) { \
intr = new Bp##INTERFACE(obj); \
} \
} \
return intr; \
} \
I##INTERFACE::I##INTERFACE() { } \
I##INTERFACE::~I##INTERFACE() { }
INTERFACE实际是ServiceManager。IMPLEMENT_META_INTERFACE在IserviceManager.cpp只有这一行代码
IMPLEMENT_META_INTERFACE(ServiceManager, "android.os.IServiceManager");
我们进行相应的替换
#define IMPLEMENT_META_INTERFACE(IServiceManager, "android.os.IServiceManager")
const android::String16 IServiceManager::descriptor("android.os.IServiceManager"); \
const android::String16& \
IServiceManager::getInterfaceDescriptor() const { \
return IServiceManager::descriptor; \
} \
android::sp<IServiceManager> IServiceManager::asInterface( \
const android::sp<android::IBinder>& obj) \
{ \
android::sp<IServiceManager> intr; \
if (obj != NULL) { \
intr = static_cast<IServiceManager>( \
obj->queryLocalInterface( \
IServiceManager::descriptor).get()); \
if (intr == NULL) { \
intr = new BpServiceManager(obj); \
} \
} \
return intr; \
} \
实际最终是new了一个BpServiceManager，obj的值是bpBinder
所以最终defaultServiceManager实际返回的是BpServiceManager
- bpServiceManager是在IservieManager.cpp中创建的
class BpServiceManager : public BpInterface<IServiceManager>
{
public:
BpServiceManager(const sp<IBinder>& impl)
: BpInterface<IServiceManager>(impl)
{
}
virtual status_t addService(const String16& name, const sp<IBinder>& service,
bool allowIsolated)
{
Parcel data, reply;
data.writeInterfaceToken(IServiceManager::getInterfaceDescriptor());
data.writeString16(name);
data.writeStrongBinder(service);
data.writeInt32(allowIsolated ? 1 : 0);
//remote实际是IBinder* 指针，它最终的指向为BpBinder
status_t err = remote()->transact(ADD_SERVICE_TRANSACTION, data, &reply);
return err == NO_ERROR ? reply.readExceptionCode() : err;
}
};
status_t Parcel::writeStrongBinder(const sp<IBinder>& val)
{
return flatten_binder(ProcessState::self(), val, this);
}
status_t flatten_binder(const sp<ProcessState>& /*proc*/,
const sp<IBinder>& binder, Parcel* out)
{
flat_binder_object obj;
obj.flags = 0x7f | FLAT_BINDER_FLAG_ACCEPTS_FDS;
if (binder != NULL) {
IBinder *local = binder->localBinder();
if (!local) {
BpBinder *proxy = binder->remoteBinder();
if (proxy == NULL) {
ALOGE("null proxy");
}
} else {
//进入这里设置type为BINDER_TYPE_BINDER
obj.type = BINDER_TYPE_BINDER;
obj.binder = reinterpret_cast<uintptr_t>(local->getWeakRefs());
obj.cookie = reinterpret_cast<uintptr_t>(local);
}
} else {
}
return finish_flatten_binder(binder, obj, out);
}
inline static status_t finish_flatten_binder(
const sp<IBinder>& /*binder*/, const flat_binder_object& flat, Parcel* out)
{
return out->writeObject(flat, false);
}
transact();源码分析
status_t BpBinder::transact(
uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags)
{
// Once a binder has died, it will never come back to life.
if (mAlive) {
status_t status = IPCThreadState::self()->transact(
mHandle, code, data, reply, flags);
if (status == DEAD_OBJECT) mAlive = 0;
return status;
}
return DEAD_OBJECT;
}
status_t IPCThreadState::transact(int32_t handle,
uint32_t code, const Parcel& data,
Parcel* reply, uint32_t flags)
{
if (err == NO_ERROR) {
//传输数据
err = writeTransactionData(BC_TRANSACTION, flags, handle, code, data, NULL);
}
if ((flags & TF_ONE_WAY) == 0) {
if (reply) {
//等待回复
err = waitForResponse(reply);
} else {
Parcel fakeReply;
err = waitForResponse(&fakeReply);
}
} else {
//aidl的onWay不需要等待
err = waitForResponse(NULL, NULL);
}
return err;
}
status_t IPCThreadState::writeTransactionData(int32_t cmd, uint32_t binderFlags,
int32_t handle, uint32_t code, const Parcel& data, status_t* statusBuffer)
{
binder_transaction_data tr;
tr.target.ptr = 0;
//handle==0则代表ServiceManager进程
tr.target.handle = handle;
//code=ADD_SERVICE_TRANSACTION
tr.code = code;
tr.flags = binderFlags;
tr.cookie = 0;
tr.sender_pid = 0;
tr.sender_euid = 0;
//cmd是BC_TRANSACTION，ServiceManager会返回BR_TRANSACTION_COMPLETE表示通信请求已经接受，client进入等待状态
mOut.writeInt32(cmd);
//写入数据
mOut.write(&tr, sizeof(tr));
return NO_ERROR;
}
status_t IPCThreadState::waitForResponse(Parcel *reply, status_t *acquireResult)
{
uint32_t cmd;
int32_t err;
while (1) {
if ((err=talkWithDriver()) < NO_ERROR) break;
err = mIn.errorCheck();
cmd = (uint32_t)mIn.readInt32();
switch (cmd) {
case BR_TRANSACTION_COMPLETE:
if (!reply && !acquireResult) goto finish;
break;
case BR_DEAD_REPLY:
err = DEAD_OBJECT;
goto finish;
case BR_FAILED_REPLY:
err = FAILED_TRANSACTION;
goto finish;
case BR_ACQUIRE_RESULT:
{
ALOG_ASSERT(acquireResult != NULL, "Unexpected brACQUIRE_RESULT");
const int32_t result = mIn.readInt32();
if (!acquireResult) continue;
*acquireResult = result ? NO_ERROR : INVALID_OPERATION;
}
goto finish;
case BR_REPLY:
{
binder_transaction_data tr;
err = mIn.read(&tr, sizeof(tr));
ALOG_ASSERT(err == NO_ERROR, "Not enough command data for brREPLY");
if (err != NO_ERROR) goto finish;
if (reply) {
if ((tr.flags & TF_STATUS_CODE) == 0) {
reply->ipcSetDataReference(
reinterpret_cast<const uint8_t*>(tr.data.ptr.buffer),
tr.data_size,
reinterpret_cast<const binder_size_t*>(tr.data.ptr.offsets),
tr.offsets_size/sizeof(binder_size_t),
freeBuffer, this);
} else {
err = *reinterpret_cast<const status_t*>(tr.data.ptr.buffer);
freeBuffer(NULL,
reinterpret_cast<const uint8_t*>(tr.data.ptr.buffer),
tr.data_size,
reinterpret_cast<const binder_size_t*>(tr.data.ptr.offsets),
tr.offsets_size/sizeof(binder_size_t), this);
}
} else {
freeBuffer(NULL,
reinterpret_cast<const uint8_t*>(tr.data.ptr.buffer),
tr.data_size,
reinterpret_cast<const binder_size_t*>(tr.data.ptr.offsets),
tr.offsets_size/sizeof(binder_size_t), this);
continue;
}
}
goto finish;
default:
err = executeCommand(cmd);
if (err != NO_ERROR) goto finish;
break;
}
}
finish:
if (err != NO_ERROR) {
if (acquireResult) *acquireResult = err;
if (reply) reply->setError(err);
mLastError = err;
}
return err;
}
网上的图片.jpg
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