Android IPC 通讯机制源码分析

核心提示：if (reply) reply->setError(err);return (mLastError = err);}if ((flags & TF_ONE_WAY) == 0) {if (reply) {err = waitForResponse(reply);} else {Parcel fakeReply;

if (reply) reply->setError(err);

return (mLastError = err);

}

if ((flags & TF_ONE_WAY) == 0) {

if (reply) {

err = waitForResponse(reply);

} else {

Parcel fakeReply;

err = waitForResponse(&fakeReply);

}

..............................

return err;

}

通过writeTransactionData构造要发送的数据

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.handle = handle; //这个handle将传递到service_manager

tr.code = code;

tr.flags = bindrFlags;

。。。。。。。。。。。。。。

}

waitForResponse将调用talkWithDriver与对Binder kernel进行读写操作。当Binder kernel接收到数据后，service_mananger线程的ThreadPool就会启动，service_manager查找到 CameraService服务后调用binder_send_reply，将返回的数据写入Binder kernel,Binder kernel。

status_t IPCThreadState::waitForResponse(Parcel *reply, status_t *acquireResult)

{

int32_t cmd;

int32_t err;

while (1) {

if ((err=talkWithDriver()) < NO_ERROR) break;

..............................................

}

status_t IPCThreadState::talkWithDriver(bool doReceive)

{

............................................

#if defined(HAVE_ANDROID_OS)

if (ioctl(mProcess->mDriverFD, BINDER_WRITE_READ, &bwr) >= 0)

err = NO_ERROR;

else

err = -errno;

#else

err = INVALID_OPERATION;

#endif

...................................................

}

通过上面的ioctl系统函数中BINDER_WRITE_READ对binder kernel进行读写。