Native Binder 之 IServiceManager

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涉及代码：
frameworks/native/libs/binder/BpBinder.cpp
frameworks/native/libs/binder/IServiceManager.cpp

1. IServiceManager

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// frameworks/native/libs/binder/IServiceManager.cpp
class BpServiceManager : public BpInterface<IServiceManager>
{
public:
    explicit BpServiceManager(const sp<IBinder>& impl)
        : BpInterface<IServiceManager>(impl)
    {
    }
    virtual sp<IBinder> getService(const String16& name) const
    {
        sp<IBinder> svc = checkService(name);
        if (svc != nullptr) return svc;
        const bool isVendorService =
            strcmp(ProcessState::self()->getDriverName().c_str(), "/dev/vndbinder") == 0;
        const long timeout = uptimeMillis() + 5000;
        if (!gSystemBootCompleted && !isVendorService) {
            // vendor代码不能访问访问system属性。
            char bootCompleted[PROPERTY_VALUE_MAX];
            property_get("sys.boot_completed", bootCompleted, "0");
            gSystemBootCompleted = strcmp(bootCompleted, "1") == 0 ? true : false;
        }
        // 设定重试的时间间隔（毫秒），开机完成则为1s，未完成开机时为0.1s。
        const long sleepTime = gSystemBootCompleted ? 1000 : 100;
        int n = 0;
        while (uptimeMillis() < timeout) {
            n++;
            ALOGI("Waiting for service '%s' on '%s'...", String8(name).string(),
                ProcessState::self()->getDriverName().c_str());
            usleep(1000*sleepTime);
            sp<IBinder> svc = checkService(name);
            if (svc != nullptr) return svc;
        }
        ALOGW("Service %s didn't start. Returning NULL", String8(name).string());
        return nullptr;
    }
    virtual sp<IBinder> checkService( const String16& name) const
    {
        Parcel data, reply;
        data.writeInterfaceToken(IServiceManager::getInterfaceDescriptor());
        data.writeString16(name);
        remote()->transact(CHECK_SERVICE_TRANSACTION, data, &reply);
        return reply.readStrongBinder();
    }
    virtual status_t addService(const String16& name, const sp<IBinder>& service,
                                bool allowIsolated, int dumpsysPriority) {
        Parcel data, reply;
        data.writeInterfaceToken(IServiceManager::getInterfaceDescriptor());
        data.writeString16(name);
        data.writeStrongBinder(service);
        data.writeInt32(allowIsolated ? 1 : 0);
        data.writeInt32(dumpsysPriority);
        status_t err = remote()->transact(ADD_SERVICE_TRANSACTION, data, &reply);
        return err == NO_ERROR ? reply.readExceptionCode() : err;
    }
    virtual Vector<String16> listServices(int dumpsysPriority) {
        Vector<String16> res;
        int n = 0;
        for (;;) {
            Parcel data, reply;
            data.writeInterfaceToken(IServiceManager::getInterfaceDescriptor());
            data.writeInt32(n++);
            data.writeInt32(dumpsysPriority);
            status_t err = remote()->transact(LIST_SERVICES_TRANSACTION, data, &reply);
            if (err != NO_ERROR)
                break;
            res.add(reply.readString16());
        }
        return res;
    }
}

2. BpBinder

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// frameworks/native/libs/binder/BpBinder.cpp
status_t BpBinder::transact(
    uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags)
{
    // 一旦binder挂掉，则不会再复活。
    if (mAlive) {
        status_t status = IPCThreadState::self()->transact(
            mHandle, code, data, reply, flags);
        if (status == DEAD_OBJECT) mAlive = 0;
        return status;
    }
    return DEAD_OBJECT;
}