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Android 4.0里面除了个BitTube的东西,字面意思理解就是字节管道,可以用来在进程间进行数据的传递,但是是单向的
如果要在两个进程间使用BitTube进行数据的传递,一般都是这么使用的(以SensorEventConnection和SensorEventQueue通信为例)
1、首先在SensorEventConnection的构造函数里面 new 一个BitTube,不需要参数,
- SensorService::SensorEventConnection::SensorEventConnection(
- const sp<SensorService>& service)
- : mService(service), mChannel(new BitTube())
- {
- }
我们看下BitTube的构造函数
- BitTube::BitTube()
- : mSendFd(-1), mReceiveFd(-1)
- {
- int sockets[2];
- if (socketpair(AF_UNIX, SOCK_SEQPACKET, 0, sockets) == 0) { //创造一对未命名的、相互连接的UNIX域套接字
- int size = SOCKET_BUFFER_SIZE;
- setsockopt(sockets[0], SOL_SOCKET, SO_SNDBUF, &size, sizeof(size));
- setsockopt(sockets[0], SOL_SOCKET, SO_RCVBUF, &size, sizeof(size));
- setsockopt(sockets[1], SOL_SOCKET, SO_SNDBUF, &size, sizeof(size));
- setsockopt(sockets[1], SOL_SOCKET, SO_RCVBUF, &size, sizeof(size));
- fcntl(sockets[0], F_SETFL, O_NONBLOCK);//设置为非阻塞
- fcntl(sockets[1], F_SETFL, O_NONBLOCK);//设置为非阻塞
- mReceiveFd = sockets[0];//用于数据接收的socket
- mSendFd = sockets[1];//用于数据发送的socket
- } else {
- mReceiveFd = -errno;
- ALOGE("BitTube: pipe creation failed (%s)", strerror(-mReceiveFd));
- }
- }
里面主要就是创建了一对未命名的互连的套接字,并设置为非阻塞的
2、然后,我们就可以使用这个BitTube了,这里这里在SensorEventQueue的onFirstRef调用时,
- void SensorEventQueue::onFirstRef()
- {
- mSensorChannel = mSensorEventConnection->getSensorChannel();
- }
通过getSensorChannel获取SensorEventConnection端面的BitTube我们看一下这个函数的实现,从Bp端面到Bn端
- virtual sp<BitTube> getSensorChannel() const
- {
- Parcel data, reply;
- data.writeInterfaceToken(ISensorEventConnection::getInterfaceDescriptor());
- remote()->transact(GET_SENSOR_CHANNEL, data, &reply);
- return new BitTube(reply);
- }
利用返回值new 一个新的BitTube
- BitTube::BitTube(const Parcel& data)
- : mSendFd(-1), mReceiveFd(-1)
- {
- mReceiveFd = dup(data.readFileDescriptor());
- if (mReceiveFd >= 0) {
- int size = SOCKET_BUFFER_SIZE;
- setsockopt(mReceiveFd, SOL_SOCKET, SO_SNDBUF, &size, sizeof(size));
- setsockopt(mReceiveFd, SOL_SOCKET, SO_RCVBUF, &size, sizeof(size));
- fcntl(mReceiveFd, F_SETFL, O_NONBLOCK);
- } else {
- mReceiveFd = -errno;
- ALOGE("BitTube(Parcel): can't dup filedescriptor (%s)",
- strerror(-mReceiveFd));
- }
- }
利用readFileDescriptor读取描述符,然后设置mReceiveFd
3、我们看一下相应的Bn端是怎么实现的
- status_t BnSensorEventConnection::onTransact(
- uint32_t code, const Parcel& data, Parcel* reply, uint32_t flags)
- {
- switch(code) {
- case GET_SENSOR_CHANNEL: {
- CHECK_INTERFACE(ISensorEventConnection, data, reply);
- sp<BitTube> channel(getSensorChannel());
- channel->writeToParcel(reply);
- return NO_ERROR;
- } break;
- ….
- }
调用getSensorChannel返回我们在第一步中new出来的BitTube,然后调用BitTube的writeToParcel
- status_t BitTube::writeToParcel(Parcel* reply) const
- {
- if (mReceiveFd < 0)
- return -EINVAL;
- status_t result = reply->writeDupFileDescriptor(mReceiveFd);
- close(mReceiveFd);
- mReceiveFd = -1;
- return result;
- }
其实就是将其mReceiveFd描述符返回过去
通过这几步我们就可以在SensorEventConnection中发送数据,
ssize_tSensorEventQueue::write(const sp<BitTube>& tube,
ASensorEvent const* events, size_tnumEvents) {
return BitTube::sendObjects(tube, events,numEvents);
}
这里的tube参数就是我们第一步创建的
然后在SensorEventQueue读取数据
- ssize_t SensorEventQueue::read(ASensorEvent* events, size_t numEvents)
- {
- return BitTube::recvObjects(mSensorChannel, events, numEvents);
- }
这里的mSensorChannel就是我们上面第二步创建的。
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