PHP inter-process communication--named pipe

PHP pipeline communication
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There are several ways for PHP to communicate between processes: message queue ,pipeline,shared memory,socket,signal. This article introduces the method through famous pipes.

 PIPE

 Pipes are used to carry communication data between abbreviations. To facilitate understanding, a pipe can be compared to a file. Process A writes data to pipe P, and then process B reads data from pipe P. The pipeline operation API provided by PHP is basically the same as the API for operating files. Except that the posix_mkfifo function is used to create a pipeline, the read and write operations are the same as the file operation functions. Of course, you can use files to simulate pipes directly, but then you won't be able to use the features of pipes.

The general idea of ​​communicating through a pipe is to first create a pipe, then the child process writes information to the pipe, and the parent process reads the information from the pipe. In this way, the parent and child processes can communicate directly. <?php<br>/**<br> * author: NickBai<br> * createTime: 2016/12/2 0002 AM 11:12<br>*/<br>//Create pipe <br>$pipePath = "/tmp/test.pipe";<br>if( !file_exists( $pipePath ) ){<br> if( !posix_mkfifo( $ pipePath, 0666 ) ){<br> exit('make pipe false!' .PHP_EOL);<br> }<br>}<br><br>//Create a process, the child process writes the pipe, and the parent process reads the pipe<br>$pid = pcntl_fork();<br><br>if ( $pid == 0 ){<br> //Sub-process write pipe<br> $file = fopen( $pipePath, 'w' );<br> fwrite( $file, 'hello world' );<br> sleep(1);<br> exit( );<br>}else{<br> //The parent process reads the pipe<br> $file = fopen($pipePath, 'r');<br> //stream_set_blocking($file, False); //Set to read non-blocking<br> echo fread( $file, 20 ) . PHP_EOL;<br><br> pcntl_wait($status); //Recycle child process <br>} Note: This code can only be run under linux, and can only be run in php-cli mode.
Line 7: Specify the path of a pipeline, which is no different from an ordinary file.

　 Line 9: Create a pipe through the posix_mkfifo function and set the read and write permissions to 0666

Line 15: Create a child process through the pcntl_fork function. Note that from now on, the program will be executed in two processes. The pcntl_fork function is very special. It has multiple return values ​​once called. In the parent process: it returns the ID of the child process. This value is greater than 0. In the child process, it returns 0. When -1 is returned, it indicates that the creation process failed.

Line 17: The two processes enter different branches based on the different $pid values ​​obtained by the current process.

Lines 18~22: The child process opens the pipe, writes hello world to it, then enters sleep, and exits after the sleep ends.

Lines 25~29: The parent process opens the pipe and reads it, and finally executes line 29 of code to recycle the child process. There are two places here that are blocked. The first is the default reading place. You have to wait for the child process to issue an exit command before the data can be returned. There is also the pcntl_wait method of recycling the process. Wait until the process exits.

　 Run this code under Linux:

You will see that the program blocks for 1 second and then outputs hello world.

　When we open the 26th line of code and change the 27th line to var_dump(fread($file, 20)) .PHP_EOL;, run the program:

You can see that the program immediately outputs an empty string and waits for 1 second Exit after success. This is because. When reading is non-blocking, when the parent process reads information, it will not wait for information to be available immediately. If there is no information in the pipeline, it will return immediately. Then when line 29 is executed to recycle the child process, it blocks and waits for the child process to exit.

Let’s look at a simple practical example. Two child processes write information to a file. The parent process is responsible for monitoring and detecting whether the writing of the file is completed. After completion, make a copy of the file. Here, the parent and child processes communicate through pipes to confirm whether the writing is completed. <?php<br>/**<br> * author: NickBai<br> * createTime: 2016/12/2 0002 PM 2:00<br>*/<br>//Create pipe<br>$pipePath = "/tmp/test.pipe";<br>if(!file_exists($pipePath)){<br> if(!posix_mkfifo($pipePath, 0666)){<br> exit("make pipe fail n");<br>}<br>}<br><br>//Create two sub-processes to write files<br>for ( $i = 0; $i < 2; $i++ ){<br><br> $pid = pcntl_fork();<br> if( $pid == 0){<br> file_put_contents( './pipe.log', $i . " write pipen", FILE_APPEND ); //Write a file <br>         $file = fopen(  $pipePath, 'w'  ); <br>         fwrite(  $file,  $i . "n"  );                              Entry completed. (Fclose ($ file); <br> exit (); // Exit the sub -process}}}} // The father's process must be done: <br> // Finished<br>//2. Copy the written file<br>//3. Delete the pipe<br>//4. Recycle the process<br><br>$file = fopen( $pipePath, 'r' );<br>$line = 0;<br>while(1 ){<br> $end = fread( $file, 1024);<br> foreach(str_split($end) as $c) {<br> if ("n" == $c) {<br> $line++;<br> <br> }<br><br> if ( $line == 2 ){<br>       copy( './pipe.log', './pipe_copy.log' ); <br> exit("ok n");<br> }<br>}<br><br><br><br><br> <br>