Shulou(Shulou.com)06/01 Report--

one。 Overview:

Blocking, non-blocking, synchronization, and asynchronism are often mentioned in network programming. Let me first talk about blocking, non-blocking, synchronization and asynchronism in Ibank O as I understand them.

The five models are blocking Imax O, non-blocking Imax O, signal driven, Imax O multiplexing (these four models are synchronous Imax O), and asynchronous Imax O.

Let me give you an example to explain these five Imax O models:

There are five people fishing:

A uses the most old-fashioned fishing rod, so you have to keep it until the fish takes the bait. (blocking Istroke O)

B, its fishing rod is relatively new, so he is not afraid to pull it away after the fish take the bait, so he looks at his mobile phone from time to time to see if there is a fish on the rod, and if so, he pulls the rod quickly. (non-blocking Istroke O)

C's fishing rod has a function to show whether any fish have taken the bait, so B will chat with the next MM and see if any fish take the bait, and pull the rod quickly if any. (signal driven)

D used a fishing rod similar to C, but he came up with a good idea, that is, he put several rods at the same time, and then stood by. Once it was shown that the fish had taken the bait, it would pull up the corresponding rod.

E is a rich man (the rich man is amazing), so he simply hired a person to help him fish. Once that person caught the fish, he sent a text message to E. (asynchronous IPUBO)

Let me first talk about blocking, non-blocking, synchronization, and asynchronism as I understand it.

II. I / O operation process:

First of all, the hardware is involved in performing the IWeiO operation, so you will deal with the operating system. (reading / sending data from the network card to the network is done by the operating system.) therefore, first explain the following I understand the IAccord O process (generally speaking, wait for the data and data relocation process)

First of all, the API function is called by the system (in user mode). The function waits for the data in the cache, and the operating system monitors the cache (kernel state at this time). When the data is received in the cache, the operating system first notifies the function to call (enter the user state), and then some packaged functions are called in the implementation of this function. The "these" function copies the data from the kernel to the user cache (first to the kernel state, then to the user mode), and then the function returns.

The details are as follows:

Blocking, non-blocking, synchronous, asynchronous in triple I / O operation:

(1)。 Synchronization: synchronization means that when a function is called, the call does not return until the call gets a result. (in read O operations, such as calling the read function, this function will be blocked in the call to the read function, but the kernel has been doing something related to read, that is, the function is activated (it takes up cpu), but on the face of it it hasn't been returned yet.

(2)。 Blocking: a blocking call is a call to a function, and the thread executing the function is suspended before the result of the call is obtained (in this state, cpu does not allocate a time slice to the function) and does not return until the result is obtained.

(3)。 Non-blocking: this means that if a function does not get a result immediately, the function does not block the thread and returns immediately.

(4)。 Async: it means that when a function call is called, the call will not immediately get the result, nor will it block the thread. The thread in which the call is made will continue to perform other things, and this function is done by other executing parts. When this part completes the function, it notifies the caller through status, notification, or handles the call through the callback function.

The executor and the caller can return the results in three ways:

a. Status,

b. Notice,

c. Callback function.

Which one to use depends on the implementation of the execution part, which is not controlled by the caller unless the execution part provides multiple options.

a. If the executing part is notified by status

Then the caller needs to check it at regular intervals, and the efficiency is very low.

b. If it is the way of using notification

Efficiency is high because there is little need to do extra work to execute the component.

c. As for the callback function

It's not much different from a notice.

four。 Five Icano models: (having understood the above knowledge, it should be easier to understand below)

(1)。 Blocking Ihamo:

The application calls an IO function, causing the application to block and wait for the data to be ready. If the data is not ready, keep waiting. . The data is ready and copied from the kernel to user space, and the IO function returns a success indication.

As shown below:

(2)。 Non-blocking Istroke O:

In the case of non-blocking Istroke O, it is important to place an Istroke O operation function in an endless loop until the Iamp O function returns a correct value.

Setting a SOCKET interface to non-blocking tells the kernel not to sleep the thread but to return an error when the requested Imax O operation cannot be completed. In this way, our Iwhite O operation function will continue to test whether the data is ready, and if not, continue to test until the data is ready. In this continuous testing process, it will take up a lot of CPU time.

As shown below:

(3)。 Signal driven:

First, the interface is allowed to signal-drive Ihand O, and then a signal handler is installed so that the thread continues to run without blocking. When the data is ready, the thread receives a SIGIO signal that can be called in the signal processing function to process the data.

As shown below:

(4) I / O reuse:

The select, poll and epoll functions will be used in the Imax O reuse model, which will also block the process, but unlike blocking IBO, these functions can block multiple Imax O operations at the same time. Moreover, multiple read operations and multiple write operations can be detected at the same time, and the Icano operation function is not really called until there is data to read or write. (it does not have any advantage over blocking Ithumb O, but it enables snooping of multiple Imax O ports.)

As shown below:

(5)。 Asynchronous IPUBO:

When an asynchronous procedure call is made, the caller cannot get the result immediately. The part that actually handles the call notifies the caller of the input and output operation through status, notification, and callback after completion.

As shown below:

six。 Comparison of five Icano models:

seven。 Summary:

To understand the five Ihammer O models, we should first understand the operation process of Iripple O, and understand some knowledge of blocking, non-blocking, synchronization and asynchronism.

Igamo operation has to deal with hardware, so the operating system will be involved in the process of Igamot O operation.

There are two processes to deal with the Icano operation, one is to wait for the data, and the other is to move the data from the kernel to the user space.

The difference between these five models is that the way of waiting for data is the same in the second process, which is to move the data from the kernel to the user space, and then carry out related operations.

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.