鸿蒙OpenHarmony技术—消息机制实现

本文介绍: 以上的核心就是基于poll，通过ioctl来读取消息(HDF_READ_DEV_EVENT)，然后再去调用上面传过来的回调函数。重点就是通过HdfIoServiceBind绑定服务，调用服务的Dispatch接口。主要是通过HdfDeviceRegisterEventListener注册回调函数。最底层就是通过系统调用ioctl来读写消息(HDF_WRITE_READ)。这里主要看用户态的实现，即hdf_syscall_adapter.c。

用户态主要代码

struct HdfIoService *serv = HdfIoServiceBind(SAMPLE_SERVICE_NAME);


......


ret = serv->dispatcher->Dispatch(&serv->object, SAMPLE_WRITE_READ, data, reply);
if (ret != HDF_SUCCESS) {
    HDF_LOGE("fail to send service call");
    goto out;
}

重点就是通过HdfIoServiceBind绑定服务，调用服务的Dispatch接口

HdfIoServiceBind接口的主要作用是open对应服务的字符设备节点/dev/hdf/serviceName，细节流程如下：

SHELL
HdfIoServiceBind(`drivers/hdf_core/framework/core/shared/src/hdf_io_service.c`)
    -> HdfIoServiceAdapterObtain
        -> open /dev/hdf/serviceName
        -> .Dispatch = HdfSyscallAdapterDispatch

HdfIoServiceAdapterObtain函数有两处实现：

这里主要看用户态的实现，即hdf_syscall_adapter.c

SHELL
serv->dispatcher->Dispatch()
dispatcher 
    -> Dispatch()
        -> HdfSyscallAdapterDispatch 
            -> ioctl - HDF_WRITE_READ

最底层就是通过系统调用ioctl来读写消息(HDF_WRITE_READ)。

struct HdfIoService *serv = HdfIoServiceBind(SAMPLE_SERVICE_NAME);


......


static struct HdfDevEventlistener listener = {
    .callBack = OnDevEventReceived,
    .priv ="Service0"
};


if (HdfDeviceRegisterEventListener(serv, &listener) !=          HDF_SUCCESS) {
    HDF_LOGE("fail to register event listener");
    return HDF_FAILURE;
}

SHELL
HdfDeviceRegisterEventListener
    -> HdfDeviceRegisterEventListenerWithSchedPolicy
        -> HdfIoServiceStartListen
            -> HdfIoServiceThreadBindLocked
                -> HdfDevListenerThreadInit
                    -> HdfDevListenerThreadDoInit
                        -> OsalThreadCreate HdfDevEventListenTask
            -> HdfDevListenerThreadStart
                -> HdfAdapterStartListenIoctl  
                    -> ioctl  - HDF_LISTEN_EVENT_START
                -> OsalThreadStart HdfDevEventListenTask

SHELL
HdfDevEventListenTask  - poll
    -> HdfDevEventReadAndDispatch  
        -> ioctl - HDF_READ_DEV_EVENT
        -> HdfDevEventDispatchLocked
            -> listener->callBack