| Input / Output Process IO | IO ready and waiting for the event to copy data | Characteristics, advantages and disadvantages |
|---|---|---|
| Blocking IO | The kernel before the data is ready, the system call will wait. | All sockets, the default is blocking the way. |
| Non-blocking IO | If the kernel is not yet the data is ready, the system call will return an error directly. | Programmers need to repeat determination IO event is ready, on the CPU consumption is relatively serious. |
| IO drive signal | Core data are ready, use SIGIO signal notifies the application program IO operations. | Operating system IO operations signaled application |
| Asynchronous IO | The completion of the data copying in the kernel notifies the application. | The data copying is done by the system, no waiting time. |
1. blocking I / O model
talk of the town to the train station to buy tickets, line up three days to buy a refund.
Cost: stop eating and drinking Lazard sleep in three days, one did not do other things.
2. Non-blocking I / O model
talk of the town to the train station to buy a ticket, every 12 hours to the train station asked whether or not a refund, three days later to buy a ticket.
Cost: round-trip station six times, six hours on the road, a lot of time to do other things.
3.I / O multiplexing model
1.select/poll
talk of the town to the train station to buy a ticket, commissioned by cattle, then every 6-hour telephone inquiry cattle, cattle to buy tickets within three days, and then talk of the town to the train station to pay for tickets .
Cost: round-trip station 2, on the road two hours, cattle fee $ 100, call 17 times
2.epoll
talk of the town to the train station to buy a ticket, commissioned by cattle, cattle buy talk of the town after notification to pick up, then go talk of the town Station pay to get tickets.
Cost: round-trip station 2, on the road two hours, cattle fee $ 100, without having to call
4. The signal driven I / O model
talk of the town to the train station to buy a ticket, the conductor to leave your phone, after the vote, conductor hear his phone call, then talk of the town to the train station to pay for tickets.
Cost: round-trip station 2, on the road two hours, costs 100 yuan cattle-free, without having to call
5. asynchronous I / O model
talk of the town to the train station to buy a ticket, the conductor to leave your phone, after the vote, conductor hear his phone call and express home delivery.
Cost: 1 and from the station, on the road for one hour costs 100 yuan cattle-free, no phone calls
If an I / O stream in, we will start a process to handle the I / O stream. Now, I assume there are now one million I / O stream in, then we need to turn one million one correspondence process to deal with these I / O stream (which is in the traditional sense of the multi-process concurrent processing ). Think about one million process, your CPU usage will be high, the implementation is extremely unreasonable. Therefore, there has been proposed I / O multiplexing model, a thread, by recording the status of I / O stream to manage a plurality of I / O, can increase throughput capacity of the server.