This topic has been talked about for a long time. Among the abilities that must be assessed in interviews, I personally think that problem-solving ability ranks first, and has a higher priority than learning ability. The ability to solve problems can not only show the programmer's thinking ability, adaptability, exploration ability, etc., but also his experience. If you have poor problem-solving skills, you will not be able to pass the interview.
Here is an example, if I execute a PHP script, such as php test.php, it is expected to return a string. But no information is output after execution. How can we know where the program is wrong? The problem-solving ability can be divided into 8 levels here. The higher the level, the stronger the ability.
Lv0 View PHP error message
The program did not achieve the expected results, which proves that the code is wrong. Looking at the PHP error message is the first step. If you ignore the error message, it indicates that this person is not suitable for a professional programmer position. In some cases, the error display is turned off in the php.ini configuration, and you need to modify php.ini to open the error message, or the error message is exported to a log file. In this case, you can directly tailf php_error.log to see the error message.
After getting the error message, directly locate the program code problem, or search on Google/Baidu to solve the problem.
Note: The method to turn on the error display is
Set display_errors / display_startup_errors in php.ini to On
php.ini error_reporting is set to E_ALL
Set error_reporting(E_ALL) in PHP code
Lv1 There are multiple versions of php or php-cli and php-fpm load different configurations
There are multiple versions of php, know which PHP it is through which php, or add an absolute path to specify the php version. Indicates that this PHPer has passed 50% of the tests at this level.
Another situation is that the execution results obtained by php-cli and php-fpm are different. For example, the execution in the web browser is correct, but the execution in cli is wrong. At this time, it may be caused by the php.ini loaded in the two environments being different. Under cli, use php -i |grep php.ini to get which php.ini is loaded. The absolute path of php.ini can be obtained through the phpinfo() function under fpm.
Lv2 var_dump/die print variable value information single-step debugging
This is a commonly used method for program debugging, and it is also the simplest, crudest and most effective way to solve problems. A more advanced method is to use PHP's Trace class/log class. For a more fancy method, you can use phpstorm xdebug to debug in the IDE tool.
The Trace tool can also analyze the time consumption of scripts and optimize the performance of PHP programs.
All three tests have been passed, indicating that this programmer has the problem-solving abilities that a professional PHP programmer should have. As long as PHP programmers have passed this level, they will be able to cope with most situations and have no pressure on small and medium-sized websites.
Lv3 Use strace tool to track program execution
strace can be used to view the execution of system calls, use strace php test.php, or strace -p process ID. strace can help you see the essence through the phenomenon and grasp the process of program execution. This method is most commonly used in large websites and large companies. If you don't know strace, all I can say here is sorry, we don't accept PHPer who doesn't know strace.
strace is actually a test of the programmer's basics. If you don't know how to operate the operating system and don't understand the underlying layer at all, you will definitely not be able to use strace. Of course, strace cannot solve the infinite loop in PHP code. For example, if you find that the CPU of a php-fpm process is 100%, strace may not be able to solve it. Because strace looks at system calls, which are generally IO operations. Since it is IO intensive, the CPU cannot be 100%.
Lv4 uses the tcpdump tool to analyze the network communication process
tcpdump can capture the data communication process of the network card, and even the data content can be captured. You can use tcpdump to see what the network communication process looks like, when the TCP SYN 3-way handshake is initiated, when the FIN packet is sent, and when the RST packet is sent. This is a basic skill. If you don’t understand tcpdump, it proves that you do not have the ability to solve network problems.
Lv5 statistical function call time consumption and success rate
Use xhporf/xdebug to export the calling process of PHP requests, and then analyze the process and time consumption of each function call. Able to analyze performance bottlenecks of PHP programs and find points that can be optimized.
Another call to the network service , such as mysql query, curl, other API calls, etc., started by recording And at the end of microtime, if false is returned, you can get whether the call was successful and how much time it took. If the data can be summarized and the success rate, failure rate, and average delay of calls can be sorted out, it proves that this programmer is sensitive to interface quality and has experience in large-scale website projects.
Lv6 gdb use
gdb is a powerful tool for debugging C/C programs. Programmers need to have certain C/C skills to be able to use gdb proficiently. The strace mentioned above cannot track php program CPU100%, but gdb can track it. In addition, gdb can also solve the problem of core dump of php program. By gdb -p process ID, combined with php-src's .gdbinit zbacktrace and other tools, you can easily
track the execution of the PHP program. Like the CPU 100% above, it is often an infinite loop that occurs in the PHP program. If you check it multiple times with gdb, you can roughly get the location of the infinite loop. There are very few PHP programmers with the ability to solve problems with gdb. If you can use gdb to solve PHP problems, this PHPer can pass the interview 100% and get a higher technical rating.
Lv7 View PHP kernel and extension source codeIf you are familiar with the PHP kernel and extended
source code, you will be able to solve the most complex memory errors in PHP programs. Such PHP programmers are rare. With the gdb tool and familiarity with PHP source code, you can view opcode information, execute_data memory, the status of global variables, etc.
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