Combined with the php ob function to understand the buffering mechanism, phpob_PHP tutorial

Combined with the php ob function to understand the buffering mechanism, phpob

For a PHP programmer who has just started, the PHP buffer is almost transparent. In their minds, with an echo print_r function, the data will fly to the browser with a 'swish' sound and be displayed. I have always thought so simply. In fact, in the world of technology, things have always progressed from simplicity to complexity. Maybe those technology developers started out as simple as you and me, but in the face of the cruel reality, they had to adjust their strategies in order to improve the operating efficiency of the machine. Finally, they thought of those things that make the machine more efficient. An idea we admire.

When it comes to buffering, that is, buffer, we must compare it with cache. Simply comparing definitions is meaningless. Why not look at what they do. Caching solves the problem of how to quickly find and utilize data and save CPU consumption, while buffering solves the problem of mismatch between high-speed CPU and low-speed I/O devices.

Let’s talk about the other protagonist of this article, the ob function. ob is the abbreviation of output_buffering. Since the ob function is a PHP extension function, the ob function mainly operates the PHP buffer.

After briefly talking about the two protagonists of this article, we must return to the starting topic. How does the data output by the echo print_r function reach the browser for the user to see? The actual process is this:

echo, print_r=>php output_buffering=>webServer buffer=>browser buffer=>browser display

　We can clearly see that from the echo and print_r functions to sending information to the client, it has gone through two buffers, and the client has also gone through a browser buffer. Our main discussion in this article is php output_buffering.

　Buffer usage when the ob function is not used

Our codes often do not use the ob function at all, so do they use buffers? This depends on the php settings. The buffer is controlled through the output_buffering variable in php.ini. Its default value is off and can be set to on to open the buffer. After calling the buffer, even if the ob function is not used in the program, the code actually uses the buffer. In addition, regardless of the setting of output_buffering in php.ini, php in cli mode is always turned off by default.

Why is it a buffer? To put it simply, the high-speed CPU has processed its own data early and wants to transmit it to the user through the line, but the line is too narrow and cannot be transmitted at once. If a buffer is introduced, the CPU can quickly put the generated data into the buffer, and then rest somewhere cool. The buffer outputs data in a timely manner according to the command . This effectively solves the contradiction between high-speed CPU and low-speed I/O devices.

When will the data in the buffer be output? 1. When the buffer is full, the buffer has a capacity, and the content will be automatically output when the limit is reached. 2. The script execution is completed. Many small programs don't output that much content, so you can't wait until the buffer is full before outputting ~ This is natural.

　Buffer usage when using the ob function

　ob_start()

Turn on output buffering. This function is one of the functions we call most. With output_buffering set to on or x k, this function does not so much open the output buffer as it expands the output buffer to a large size. Of course, under the condition that output_buffering is set to off, ob_start will play the role of opening the buffer. ob_start() can also pass an optional parameter output_callback function, which is explained in detail in the official PHP manual.

ob_get_contents()

　Just get the contents of the output buffer, but don't clear it.

　ob_end_clean() and ob_clean()

The difference between these two functions can be seen literally. The former clears the buffer contents and closes it, while the latter only does the clearing work. It should be noted that after using these two functions, the previous functions such as echo and print_r will not output the content.

The author once tried to print out the contents of ob_get_contents() through print_r, and then called ob_clean() to clear the buffer so as not to affect subsequent operations on the buffer, but failed repeatedly. If you think about it carefully, the content of print_r is written to the buffer again, and the ob_clean() operation is performed later, so naturally there will be no output. Calling the ob_flush() function before the ob_clean operation can achieve the desired effect.

ob_flush() and flush()

ob_flush() sends the contents of the buffer and discards the contents. Therefore, it is best to use ob_get_contents() to obtain the buffer contents before this function. flush() flushes out the server-side buffer and sends it to the client. Therefore, from a process perspective, ob_flush() should be called first and then the flush function.

In addition, let’s explain the working principle of Apache buffer flush(): under the sapi of apache module, flush will indirectly use apache’s api: ap_rflush to refresh apache’s output buffer by calling the flush member function pointer of sapi_module(). . Of course, other Apache modules such as mod_gzip may change the result of this action and may perform the output buffer themselves. This will cause the results generated by the flush() function to not be immediately sent to the client browser.

　ob_get_clean()

　If you are already proficient in ob_get_contents() and ob_clean(), then this function is very simple. Because it is a combination of the first two. It mainly gets the contents of the current buffer and deletes the current output buffer.

There are many more ob functions, but most of them are relatively simple to use and easy to understand. You can refer to the php manual, which will have detailed explanations. This article lists some functions that the author did not understand very well at first. Of course, new problems will arise in the future. Thinking of problems and solving them may be the joy of life here.

　

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