本文基于 android10_r41 版本分析。
死亡通知的基本流程
死亡通知是为了让 Bp 端(客户端进程)能知晓 Bn 端(服务端进程)的生死情况，当 Bn 端进程死亡后能通知到 Bp 端。
分析源码之前，我们需要明确"死亡通知"实际是一个回调过程：
- 客户端，构造并保存好"死亡回调对象"，接着把"死亡回调对象"发送给驱动
- 驱动保存好"死亡回调对象"，同时记录好"死亡回调对象"对应的客户端和服务端
- 当服务端进程"挂掉"了，会执行进程的清理函数，清理函数会调用到 binder 驱动的清理函数，驱动清理函数会找到使用了服务端服务的客户端，并找到对应的客户端，最后驱动把服务端死亡消息发送给客户端，客户端调用死亡通知回调
死亡通知的注册
这里我们以 AMS 为例，来看看死亡通知的注册过程，AMS 服务对应的客户端程序通过调用 attachApplication 方法来注册死亡通知：
java
// aidl 中定义的接口
// frameworks/base/core/java/android/app/IActivityManager.aidl
void attachApplication(in IApplicationThread app, long startSeq);
// frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
// 接口的服务端实现
// 这是一个远程过程调用函数的服务端实现（Bn端实现）
@Override
public final void attachApplication(IApplicationThread thread, long startSeq) {
if (thread == null) {
throw new SecurityException("Invalid application interface");
}
synchronized (this) {
int callingPid = Binder.getCallingPid();
final int callingUid = Binder.getCallingUid();
final long origId = Binder.clearCallingIdentity();
// 具体功能是通过调用 attachApplicationLocked
attachApplicationLocked(thread, callingPid, callingUid, startSeq);
Binder.restoreCallingIdentity(origId);
}
}
// IApplicationThread 是客户端传递给服务端的匿名 Binder（或者叫 Binder 回调），当前位置是一个 Bp 代理对象
// 实际调用的是 attachApplicationLocked
// frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
private boolean attachApplicationLocked(@NonNull IApplicationThread thread,
int pid, int callingUid, long startSeq) {
ProcessRecord app;
//......
try {
//构造死亡通知回调对象
AppDeathRecipient adr = new AppDeathRecipient(app, pid, thread);
//注册死亡通知到内核
// thread.asBinder() 返回的是一个 BinderProxy 对象
// 接着调用 linkToDeath 注册死亡通知
thread.asBinder().linkToDeath(adr, 0);
app.deathRecipient = adr;
} catch (RemoteException e) {
app.resetPackageList(mProcessStats);
mProcessList.startProcessLocked(app,
new HostingRecord("link fail", processName));
return false;
}
//......
}linkToDeath 是一个 native 方法：
java
// frameworks/base/core/java/android/os/BinderProxy.java
public final class BinderProxy implements IBinder {
public native void linkToDeath(DeathRecipient recipient, int flags)
throws RemoteException;
}其第一个参数是 AppDeathRecipient ，是一个死亡通知回调对象，其实现如下，其核心是 binderDied 方法，当服务端进程挂掉时，就会回调该对象的 binderDied 方法，具体怎么调用的，我们稍后来做分析：
java
private final class AppDeathRecipient implements IBinder.DeathRecipient {
final ProcessRecord mApp;
final int mPid;
final IApplicationThread mAppThread;
AppDeathRecipient(ProcessRecord app, int pid,
IApplicationThread thread) {
if (DEBUG_ALL) Slog.v(
TAG, "New death recipient " + this
+ " for thread " + thread.asBinder());
mApp = app;
mPid = pid;
mAppThread = thread;
}
@Override
public void binderDied() {
if (DEBUG_ALL) Slog.v(
TAG, "Death received in " + this
+ " for thread " + mAppThread.asBinder());
synchronized(ActivityManagerService.this) {
appDiedLocked(mApp, mPid, mAppThread, true);
}
}
}linkToDeath 对应的 JNI 函数是：
java
// frameworks/base/core/jni/android_util_Binder.cpp
static void android_os_BinderProxy_linkToDeath(JNIEnv* env, jobject obj,
jobject recipient, jint flags) // throws RemoteException
{
if (recipient == NULL) {
jniThrowNullPointerException(env, NULL);
return;
}
//拿到 BinderProxy 对应的 BpBinder 对象
BinderProxyNativeData *nd = getBPNativeData(env, obj);
// target 实际类型是 BpBinder
IBinder* target = nd->mObject.get();
LOGDEATH("linkToDeath: binder=%p recipient=%p\n", target, recipient);
if (!target->localBinder()) { //进入 if 分支
// 获取DeathRecipientList: 其成员变量 mList 记录该 BinderProxy 的 JavaDeathRecipient 列表信息
// List 的存在，说明一个 BpBinder 可以注册多个死亡回调
DeathRecipientList* list = nd->mOrgue.get();
//创建 JavaDeathRecipient 对象
sp<JavaDeathRecipient> jdr = new JavaDeathRecipient(env, recipient, list);
// 向驱动注册死亡通知
status_t err = target->linkToDeath(jdr, NULL, flags);
if (err != NO_ERROR) {
// Failure adding the death recipient, so clear its reference
// now.
jdr->clearReference();
signalExceptionForError(env, obj, err, true /*canThrowRemoteException*/);
}
}
}这里使用到了 BinderProxy 的一些内部数据，回顾一下Binder Java 层服务注册过程分析中介绍的 BinderProxy 初始化过程：
cpp
//frameworks/base/core/jni/android_util_Binder.cpp
//当前情景下， val 的类型是 BpBinder
jobject javaObjectForIBinder(JNIEnv* env, const sp<IBinder>& val)
{
if (val == NULL) return NULL;
if (val->checkSubclass(&gBinderOffsets)) {
// It's a JavaBBinder created by ibinderForJavaObject. Already has Java object.
jobject object = static_cast<JavaBBinder*>(val.get())->object();
LOGDEATH("objectForBinder %p: it's our own %p!\n", val.get(), object);
return object;
}
//构造 BinderProxyNativeData 结构体
BinderProxyNativeData* nativeData = new BinderProxyNativeData();
//死亡通知列表
nativeData->mOrgue = new DeathRecipientList;
nativeData->mObject = val;
//gBinderProxyOffsets 中保存了 BinderProxy 类相关的信息
//调用 Java 层 GetInstance 方法获得一个 BinderProxy 对象
jobject object = env->CallStaticObjectMethod(gBinderProxyOffsets.mClass,
gBinderProxyOffsets.mGetInstance, (jlong) nativeData, (jlong) val.get());
if (env->ExceptionCheck()) { //异常处理
// In the exception case, getInstance still took ownership of nativeData.
return NULL;
}
BinderProxyNativeData* actualNativeData = getBPNativeData(env, object);
if (actualNativeData == nativeData) {
// Created a new Proxy
uint32_t numProxies = gNumProxies.fetch_add(1, std::memory_order_relaxed);
uint32_t numLastWarned = gProxiesWarned.load(std::memory_order_relaxed);
if (numProxies >= numLastWarned + PROXY_WARN_INTERVAL) {
// Multiple threads can get here, make sure only one of them gets to
// update the warn counter.
if (gProxiesWarned.compare_exchange_strong(numLastWarned,
numLastWarned + PROXY_WARN_INTERVAL, std::memory_order_relaxed)) {
ALOGW("Unexpectedly many live BinderProxies: %d\n", numProxies);
}
}
} else {
delete nativeData;
}
//返回 BinderProxy
return object;
}
// DeathRecipientList 的定义
// 定义了一个 JavaDeathRecipient 的列表，封装了一些列表操作
// frameworks/base/core/jni/android_util_Binder.cpp
class DeathRecipientList : public RefBase {
List< sp<JavaDeathRecipient> > mList;
Mutex mLock;
public:
DeathRecipientList();
~DeathRecipientList();
void add(const sp<JavaDeathRecipient>& recipient);
void remove(const sp<JavaDeathRecipient>& recipient);
sp<JavaDeathRecipient> find(jobject recipient);
Mutex& lock(); // Use with care; specifically for mutual exclusion during binder death
};
// frameworks/base/core/java/android/os/BinderProxy.java
private static BinderProxy getInstance(long nativeData, long iBinder) {
BinderProxy result;
synchronized (sProxyMap) {
try {
result = sProxyMap.get(iBinder);
if (result != null) {
return result;
}
result = new BinderProxy(nativeData);
} catch (Throwable e) {
// We're throwing an exception (probably OOME); don't drop nativeData.
NativeAllocationRegistry.applyFreeFunction(NoImagePreloadHolder.sNativeFinalizer,
nativeData);
throw e;
}
NoImagePreloadHolder.sRegistry.registerNativeAllocation(result, nativeData);
// The registry now owns nativeData, even if registration threw an exception.
sProxyMap.set(iBinder, result);
}
return result;
}可以看出 BinderProxy 类涉及 Java 和 Native 两层：
接着我们再来看看 native 层的回调对象 JavaDeathRecipient：
cpp
// frameworks/base/core/jni/android_util_Binder.cpp
// 接下来我们看看 JavaDeathRecipient 对象的初始化过程
class JavaDeathRecipient : public IBinder::DeathRecipient
{
public:
// object 类型是 AppDeathRecipient，即 Java 层的回调对象
JavaDeathRecipient(JNIEnv* env, jobject object, const sp<DeathRecipientList>& list)
: mVM(jnienv_to_javavm(env)), mObject(env->NewGlobalRef(object)), //JavaDeathRecipient 保存到 mObject 成员变量中
mObjectWeak(NULL), mList(list)
{
// These objects manage their own lifetimes so are responsible for final bookkeeping.
// The list holds a strong reference to this object.
LOGDEATH("Adding JDR %p to DRL %p", this, list.get());
//将当前对象sp添加到列表 DeathRecipientList
list->add(this);
gNumDeathRefsCreated.fetch_add(1, std::memory_order_relaxed);
gcIfManyNewRefs(env);
}
//......
};JavaDeathRecipient 构造函数主要就是把死亡回调对象 JavaDeathRecipient 对象自己加入到 DeathRecipientList 中，把 Java 层的 AppDeathRecipient 对象保存到 mObject 成员中，其他都是一些打印或者引用操作。
整个过程如下图所示：
我们接着看 status_t err = target->linkToDeath(jdr, NULL, flags); 的实现：
cpp
// 向驱动注册死亡回调
// frameworks/native/libs/binder/BpBinder.cpp
status_t BpBinder::linkToDeath(
const sp<DeathRecipient>& recipient, void* cookie, uint32_t flags)
{
//构建 Obituary 对象，将回调对象保存在其内部
Obituary ob;
ob.recipient = recipient;
ob.cookie = cookie;
ob.flags = flags;
LOG_ALWAYS_FATAL_IF(recipient == nullptr,
"linkToDeath(): recipient must be non-NULL");
{
AutoMutex _l(mLock);
if (!mObitsSent) { // 没有执行过 sendObituary，则进入该方法
if (!mObituaries) {
mObituaries = new Vector<Obituary>;
if (!mObituaries) {
return NO_MEMORY;
}
ALOGV("Requesting death notification: %p handle %d\n", this, mHandle);
getWeakRefs()->incWeak(this);
IPCThreadState* self = IPCThreadState::self();
// 关注点1
//构建好数据
self->requestDeathNotification(mHandle, this);
// 关注点2
//将构建好的数据发送给驱动
self->flushCommands();
}
ssize_t res = mObituaries->add(ob); //把新构建的 Obituary 添加到 BpBinder 的 mObituaries 成员中
return res >= (ssize_t)NO_ERROR ? (status_t)NO_ERROR : res;
}
}
return DEAD_OBJECT;
}接着看关注点 1：
cpp
status_t IPCThreadState::requestDeathNotification(int32_t handle, BpBinder* proxy)
{
mOut.writeInt32(BC_REQUEST_DEATH_NOTIFICATION);
mOut.writeInt32((int32_t)handle);
mOut.writePointer((uintptr_t)proxy);
return NO_ERROR;
}将需要发送给驱动的数据写入 Parcel mOut：
- BC_REQUEST_DEATH_NOTIFICATION：命令
- handle：目标服务对应的 handle 值
- proxy：指向客户端 BinderProxy 的指针
接着看关注点 2：
cpp
void IPCThreadState::flushCommands()
{
if (mProcess->mDriverFD <= 0)
return;
talkWithDriver(false);
// The flush could have caused post-write refcount decrements to have
// been executed, which in turn could result in BC_RELEASE/BC_DECREFS
// being queued in mOut. So flush again, if we need to.
if (mOut.dataSize() > 0) {
talkWithDriver(false);
}
if (mOut.dataSize() > 0) {
ALOGW("mOut.dataSize() > 0 after flushCommands()");
}
}通过 talkWithDriver 将数据发送给驱动，talkWithDriver 在之前文章已做分析，这里不再重复，最终我们的程序会通过系统调用 ioctl 陷入内核，调用栈如下：
cpp
ioctl 应用层
-> binder_ioctl 内核层
-> binder_ioctl_write_read
-> binder_thread_write我们就从 binder_thread_write 开始分析：
cpp
static int binder_thread_write(struct binder_proc *proc,
struct binder_thread *thread,
binder_uintptr_t binder_buffer, size_t size,
binder_size_t *consumed)
{
uint32_t cmd;
struct binder_context *context = proc->context;
void __user *buffer = (void __user *)(uintptr_t)binder_buffer;
void __user *ptr = buffer + *consumed;
void __user *end = buffer + size;
while (ptr < end && thread->return_error.cmd == BR_OK) {
int ret;
if (get_user(cmd, (uint32_t __user *)ptr))
return -EFAULT;
ptr += sizeof(uint32_t);
trace_binder_command(cmd);
if (_IOC_NR(cmd) < ARRAY_SIZE(binder_stats.bc)) {
atomic_inc(&binder_stats.bc[_IOC_NR(cmd)]);
atomic_inc(&proc->stats.bc[_IOC_NR(cmd)]);
atomic_inc(&thread->stats.bc[_IOC_NR(cmd)]);
}
switch (cmd) {
// ......
case BC_REQUEST_DEATH_NOTIFICATION:
case BC_CLEAR_DEATH_NOTIFICATION: {
uint32_t target;
binder_uintptr_t cookie;
struct binder_ref *ref;
struct binder_ref_death *death = NULL;
//拿到目标进程 handle
if (get_user(target, (uint32_t __user *)ptr))
return -EFAULT;
ptr += sizeof(uint32_t);
//拿到 BpBinder 指针
if (get_user(cookie, (binder_uintptr_t __user *)ptr))
return -EFAULT;
ptr += sizeof(binder_uintptr_t);
if (cmd == BC_REQUEST_DEATH_NOTIFICATION) {
/*
* Allocate memory for death notification
* before taking lock
*/
// 给 binder_ref_death 分配内存
death = kzalloc(sizeof(*death), GFP_KERNEL);
//......
}
binder_proc_lock(proc);
// 从 proc->refs_by_desc 中找到 target（这里就是 AMS）对应的 binder_ref 结构体
ref = binder_get_ref_olocked(proc, target, false);
//......
binder_node_lock(ref->node);
if (cmd == BC_REQUEST_DEATH_NOTIFICATION) {
if (ref->death) { //已经注册了死亡回调
//native Bp可注册多个，但Kernel只允许注册一个死亡通知
binder_user_error("%d:%d BC_REQUEST_DEATH_NOTIFICATION death notification already set\n",
proc->pid, thread->pid);
binder_node_unlock(ref->node);
binder_proc_unlock(proc);
kfree(death);
break;
}
binder_stats_created(BINDER_STAT_DEATH);
INIT_LIST_HEAD(&death->work.entry);
death->cookie = cookie; // BpBinder指针，内部保存有死亡回调对象
ref->death = death; // binder_ref_death
if (ref->node->proc == NULL) { // 当目标 binder 服务所在进程已死,则直接发送死亡通知给客户端。这是非常规情况
ref->death->work.type = BINDER_WORK_DEAD_BINDER;
binder_inner_proc_lock(proc);
// 把 binder_ref_death 插入 todo 队列
binder_enqueue_work_ilocked(
&ref->death->work, &proc->todo);
// 唤醒进程去处理
binder_wakeup_proc_ilocked(proc);
binder_inner_proc_unlock(proc);
}
} else {
//......
}
binder_node_unlock(ref->node);
binder_proc_unlock(proc);
} break;
//......
}
return 0;
}- 在当前进程的 proc->refs_by_desc 中找到 AMS 对应的 binder_ref 结构体
- 构建新的 binder_ref_death 结构体，内部 cookie 指针指向传入的 BpBinder 指针，BpBinder 指针内部保存有死亡回调对象
- 将 binder_ref 结构体的 death 指针指向新构建的 binder_ref_death 结构体
- 如果目标 binder 服务所在进程已死,则直接发送死亡通知给客户端
死亡通知的触发
当 Binder 服务所在进程死亡后，会释放进程相关的资源，对于 binder 来说，会调用到 binder_release() 函数
cpp
static int binder_release(struct inode *nodp, struct file *filp)
{
struct binder_proc *proc = filp->private_data;
debugfs_remove(proc->debugfs_entry);
//向工作队列添加 binder_deferred_work
binder_defer_work(proc, BINDER_DEFERRED_RELEASE);
return 0;
}接着我们来看看 binder_defer_work 函数的具体实现：
cpp
//定义一个工作
static DECLARE_WORK(binder_deferred_work, binder_deferred_func);
static void
binder_defer_work(struct binder_proc *proc, enum binder_deferred_state defer)
{
mutex_lock(&binder_deferred_lock);
// BINDER_DEFERRED_RELEASE 写入 proc->deferred_work
proc->deferred_work |= defer;
if (hlist_unhashed(&proc->deferred_work_node)) {
hlist_add_head(&proc->deferred_work_node,
&binder_deferred_list);
//把我们定义的工作插入内核提供的共享的默认工作队列
//内核会依次读取工作队列中的工作，并执行它们
schedule_work(&binder_deferred_work);
}
mutex_unlock(&binder_deferred_lock);
}接下来我们来看看具体的工作内容：
cpp
static void binder_deferred_func(struct work_struct *work)
{
struct binder_proc *proc;
struct files_struct *files;
int defer;
do {
mutex_lock(&binder_deferred_lock);
if (!hlist_empty(&binder_deferred_list)) {
proc = hlist_entry(binder_deferred_list.first,
struct binder_proc, deferred_work_node);
hlist_del_init(&proc->deferred_work_node);
// BINDER_DEFERRED_RELEASE 从 proc->deferred_work 取出
defer = proc->deferred_work;
proc->deferred_work = 0;
} else {
proc = NULL;
defer = 0;
}
mutex_unlock(&binder_deferred_lock);
files = NULL;
if (defer & BINDER_DEFERRED_PUT_FILES) {
mutex_lock(&proc->files_lock);
files = proc->files;
if (files)
proc->files = NULL;
mutex_unlock(&proc->files_lock);
}
if (defer & BINDER_DEFERRED_FLUSH)
binder_deferred_flush(proc);
if (defer & BINDER_DEFERRED_RELEASE) //走这里
binder_deferred_release(proc); /* frees proc */
if (files)
put_files_struct(files);
} while (proc);
}
// 释放资源
static void binder_deferred_release(struct binder_proc *proc)
{
struct binder_context *context = proc->context;
struct rb_node *n;
int threads, nodes, incoming_refs, outgoing_refs, active_transactions;
BUG_ON(proc->files);
// 删除proc_node节点
mutex_lock(&binder_procs_lock);
hlist_del(&proc->proc_node);
mutex_unlock(&binder_procs_lock);
mutex_lock(&context->context_mgr_node_lock);
if (context->binder_context_mgr_node &&
context->binder_context_mgr_node->proc == proc) {
binder_debug(BINDER_DEBUG_DEAD_BINDER,
"%s: %d context_mgr_node gone\n",
__func__, proc->pid);
context->binder_context_mgr_node = NULL;
}
mutex_unlock(&context->context_mgr_node_lock);
binder_inner_proc_lock(proc);
/*
* Make sure proc stays alive after we
* remove all the threads
*/
proc->tmp_ref++;
//释放binder_thread
proc->is_dead = true;
threads = 0;
active_transactions = 0;
while ((n = rb_first(&proc->threads))) {
struct binder_thread *thread;
thread = rb_entry(n, struct binder_thread, rb_node);
binder_inner_proc_unlock(proc);
threads++;
active_transactions += binder_thread_release(proc, thread);
binder_inner_proc_lock(proc);
}
//释放binder_node
nodes = 0;
incoming_refs = 0;
while ((n = rb_first(&proc->nodes))) {
struct binder_node *node;
node = rb_entry(n, struct binder_node, rb_node);
nodes++;
/*
* take a temporary ref on the node before
* calling binder_node_release() which will either
* kfree() the node or call binder_put_node()
*/
binder_inc_node_tmpref_ilocked(node);
rb_erase(&node->rb_node, &proc->nodes);
binder_inner_proc_unlock(proc);
//重点关注点
incoming_refs = binder_node_release(node, incoming_refs);
binder_inner_proc_lock(proc);
}
binder_inner_proc_unlock(proc);
//释放binder_ref
outgoing_refs = 0;
binder_proc_lock(proc);
while ((n = rb_first(&proc->refs_by_desc))) {
struct binder_ref *ref;
ref = rb_entry(n, struct binder_ref, rb_node_desc);
outgoing_refs++;
binder_cleanup_ref_olocked(ref);
binder_proc_unlock(proc);
binder_free_ref(ref);
binder_proc_lock(proc);
}
binder_proc_unlock(proc);
//释放binder_work
binder_release_work(proc, &proc->todo);
binder_release_work(proc, &proc->delivered_death);
binder_debug(BINDER_DEBUG_OPEN_CLOSE,
"%s: %d threads %d, nodes %d (ref %d), refs %d, active transactions %d\n",
__func__, proc->pid, threads, nodes, incoming_refs,
outgoing_refs, active_transactions);
binder_proc_dec_tmpref(proc);
}
static int binder_node_release(struct binder_node *node, int refs)
{
struct binder_ref *ref;
int death = 0;
struct binder_proc *proc = node->proc;
binder_release_work(proc, &node->async_todo);
binder_node_lock(node);
binder_inner_proc_lock(proc);
binder_dequeue_work_ilocked(&node->work);
/*
* The caller must have taken a temporary ref on the node,
*/
BUG_ON(!node->tmp_refs);
if (hlist_empty(&node->refs) && node->tmp_refs == 1) {
binder_inner_proc_unlock(proc);
binder_node_unlock(node);
binder_free_node(node);
return refs;
}
node->proc = NULL;
node->local_strong_refs = 0;
node->local_weak_refs = 0;
binder_inner_proc_unlock(proc);
spin_lock(&binder_dead_nodes_lock);
hlist_add_head(&node->dead_node, &binder_dead_nodes);
spin_unlock(&binder_dead_nodes_lock);
// 遍历 node->refs 中的每个 binder_ref
hlist_for_each_entry(ref, &node->refs, node_entry) {
refs++;
/*
* Need the node lock to synchronize
* with new notification requests and the
* inner lock to synchronize with queued
* death notifications.
*/
binder_inner_proc_lock(ref->proc);
if (!ref->death) {
binder_inner_proc_unlock(ref->proc);
continue;
}
death++;
// 添加 BINDER_WORK_DEAD_BINDER 事务到客户端进程的 todo 队列中
BUG_ON(!list_empty(&ref->death->work.entry));
ref->death->work.type = BINDER_WORK_DEAD_BINDER;
binder_enqueue_work_ilocked(&ref->death->work,
&ref->proc->todo);
//唤醒客户端
binder_wakeup_proc_ilocked(ref->proc);
binder_inner_proc_unlock(ref->proc);
}
binder_debug(BINDER_DEBUG_DEAD_BINDER,
"node %d now dead, refs %d, death %d\n",
node->debug_id, refs, death);
binder_node_unlock(node);
binder_put_node(node);
return refs;
}接下来客户端被唤醒：
cpp
static int binder_thread_read(struct binder_proc *proc,
struct binder_thread *thread,
binder_uintptr_t binder_buffer, size_t size,
binder_size_t *consumed, int non_block)
{
void __user *buffer = (void __user *)(uintptr_t)binder_buffer;
void __user *ptr = buffer + *consumed;
void __user *end = buffer + size;
int ret = 0;
int wait_for_proc_work;
if (*consumed == 0) {
if (put_user(BR_NOOP, (uint32_t __user *)ptr))
return -EFAULT;
ptr += sizeof(uint32_t);
}
retry:
binder_inner_proc_lock(proc);
wait_for_proc_work = binder_available_for_proc_work_ilocked(thread);
binder_inner_proc_unlock(proc);
thread->looper |= BINDER_LOOPER_STATE_WAITING;
trace_binder_wait_for_work(wait_for_proc_work,
!!thread->transaction_stack,
!binder_worklist_empty(proc, &thread->todo));
if (wait_for_proc_work) {
if (!(thread->looper & (BINDER_LOOPER_STATE_REGISTERED |
BINDER_LOOPER_STATE_ENTERED))) {
binder_user_error("%d:%d ERROR: Thread waiting for process work before calling BC_REGISTER_LOOPER or BC_ENTER_LOOPER (state %x)\n",
proc->pid, thread->pid, thread->looper);
wait_event_interruptible(binder_user_error_wait,
binder_stop_on_user_error < 2);
}
binder_restore_priority(current, proc->default_priority);
}
//唤醒等待中的binder线程
if (non_block) {
if (!binder_has_work(thread, wait_for_proc_work))
ret = -EAGAIN;
} else {
ret = binder_wait_for_work(thread, wait_for_proc_work);
}
thread->looper &= ~BINDER_LOOPER_STATE_WAITING;
if (ret)
return ret;
while (1) {
uint32_t cmd;
struct binder_transaction_data_secctx tr;
struct binder_transaction_data *trd = &tr.transaction_data;
struct binder_work *w = NULL;
struct list_head *list = NULL;
struct binder_transaction *t = NULL;
struct binder_thread *t_from;
size_t trsize = sizeof(*trd);
binder_inner_proc_lock(proc);
if (!binder_worklist_empty_ilocked(&thread->todo))
list = &thread->todo;
else if (!binder_worklist_empty_ilocked(&proc->todo) &&
wait_for_proc_work)
list = &proc->todo;
else {
binder_inner_proc_unlock(proc);
/* no data added */
if (ptr - buffer == 4 && !thread->looper_need_return)
goto retry;
break;
}
if (end - ptr < sizeof(tr) + 4) {
binder_inner_proc_unlock(proc);
break;
}
//拿到 binder_work
w = binder_dequeue_work_head_ilocked(list);
if (binder_worklist_empty_ilocked(&thread->todo))
thread->process_todo = false;
switch (w->type) {
//......
case BINDER_WORK_DEAD_BINDER:
case BINDER_WORK_DEAD_BINDER_AND_CLEAR:
case BINDER_WORK_CLEAR_DEATH_NOTIFICATION: {
struct binder_ref_death *death;
uint32_t cmd;
binder_uintptr_t cookie;
// 拿到 binder_work 所在的 binder_ref_death
death = container_of(w, struct binder_ref_death, work);
if (w->type == BINDER_WORK_CLEAR_DEATH_NOTIFICATION)
cmd = BR_CLEAR_DEATH_NOTIFICATION_DONE;
else //走这个分支
cmd = BR_DEAD_BINDER;
cookie = death->cookie; // cookie 就是之前传入的 BpBinder 指针
binder_debug(BINDER_DEBUG_DEATH_NOTIFICATION,
"%d:%d %s %016llx\n",
proc->pid, thread->pid,
cmd == BR_DEAD_BINDER ?
"BR_DEAD_BINDER" :
"BR_CLEAR_DEATH_NOTIFICATION_DONE",
(u64)cookie);
if (w->type == BINDER_WORK_CLEAR_DEATH_NOTIFICATION) {
binder_inner_proc_unlock(proc);
kfree(death);
binder_stats_deleted(BINDER_STAT_DEATH);
} else { //走这个分支
//把该work加入到delivered_death队列
binder_enqueue_work_ilocked(
w, &proc->delivered_death);
binder_inner_proc_unlock(proc);
}
//把 BR_DEAD_BINDER 命令返回给应用层
if (put_user(cmd, (uint32_t __user *)ptr))
return -EFAULT;
ptr += sizeof(uint32_t);
//把 BpBinder 指针 返回给应用层
if (put_user(cookie,
(binder_uintptr_t __user *)ptr))
return -EFAULT;
ptr += sizeof(binder_uintptr_t);
binder_stat_br(proc, thread, cmd);
if (cmd == BR_DEAD_BINDER)
goto done; /* DEAD_BINDER notifications can cause transactions */
} break;
}
//......
return 0;
}应用层的响应内核：
cpp
status_t IPCThreadState::executeCommand(int32_t cmd)
{
BBinder* obj;
RefBase::weakref_type* refs;
status_t result = NO_ERROR;
switch ((uint32_t)cmd) {
case BR_DEAD_BINDER:
{
BpBinder *proxy = (BpBinder*)mIn.readPointer();
proxy->sendObituary();
mOut.writeInt32(BC_DEAD_BINDER_DONE);
mOut.writePointer((uintptr_t)proxy);
} break;
...
}
...
return result;
}
void BpBinder::sendObituary()
{
ALOGV("Sending obituary for proxy %p handle %d, mObitsSent=%s\n",
this, mHandle, mObitsSent ? "true" : "false");
mAlive = 0;
if (mObitsSent) return;
mLock.lock();
Vector<Obituary>* obits = mObituaries;
if(obits != nullptr) {
ALOGV("Clearing sent death notification: %p handle %d\n", this, mHandle);
IPCThreadState* self = IPCThreadState::self();
//通知内核清空死亡通知
self->clearDeathNotification(mHandle, this);
self->flushCommands();
mObituaries = nullptr;
}
mObitsSent = 1;
mLock.unlock();
ALOGV("Reporting death of proxy %p for %zu recipients\n",
this, obits ? obits->size() : 0U);
if (obits != nullptr) {
const size_t N = obits->size();
for (size_t i=0; i<N; i++) {
//发送死亡通知
reportOneDeath(obits->itemAt(i));
}
delete obits;
}
}
void BpBinder::reportOneDeath(const Obituary& obit)
{
sp<DeathRecipient> recipient = obit.recipient.promote();
ALOGV("Reporting death to recipient: %p\n", recipient.get());
if (recipient == nullptr) return;
//回调死亡通知的方法
recipient->binderDied(this);
}参考资料
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我叫阿豪，2015 年本科毕业于国防科学技术大学指挥信息系统专业，毕业后从事信息化装备的研发工作，主要研究方向是 Android Framework 与 Linux Kernel。
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