facebook hiphop php vm 实现概述(二)
从上文可知,核心的runtime环境的代码在 src/runtme/eval,本文主要简单概述此处的代码实现,下面的叙述按文件夹分类。
一、runtime:运行时的核心数据结构(符号表)
1、assoc_list.cpp 变量关联表
2、code_coverage.cpp 代码覆盖率工具
3、file_repository.cpp php文件的jit缓存
4、variable_environment.cpp 维护各个函数、变量等所属的环境(如所属的类、作用范围等)
5、variant_stack.cpp 变量栈结构(可以用于记录函数调用关系)
6、eval_state.cpp 最重要的runtime信息都收集在这里面,比如当前有哪objects、每个object有哪些method、全局函数、常量……
7、eval_object_data.h 记录一个class的信息
8、eval_frame_injection.h 函数调用中的一个栈帧
二、ext
此目录封装了往runtime中添加外部函数的方法,
三、parser
解析器,利用YACC实现的parser(EBNF语法文件是hphp.y, hphp.tab.cpp是工具生成的),此parser与compiler目录中的不同,此处主要是为语义解析服务的(可以理解TreeWalker)。对于hiphop php vm来说,语义处理就是想办法将php代码映射为c++代码(需要runtime提供大量的外部函数)。
1、hphp.y概述
文法开始符号:start
文件包含关系、语句添加等的处理在src/runtime/eval/parser/parser.cpp中, 就onXXX()此树遍历器的输出是一个AST,顶层节点是statement
四、debugger 利用socket实现的调试器
最后真正开始处理的是 void DebuggerProxy::processInterrupt(CmdInterrupt &cmd)
五、base
基本数据结构声明
六、ast
针对 parser解析出的AST进行语义处理(即具体的对每一层树节点 将php代码转为c++代码)
每个statement的统一接口是
virtual Statement *optimize(VariableEnvironment &env) { return NULL; } // 优化语句
virtual void eval(VariableEnvironment &env) const = 0; // 处理语句关系
virtual void byteCode(ByteCodeProgram &code) const; //
dump(std::ostream &out) const = 0; // 输出c++的代码
PS:
Eval::Construct 发展出的继承结构写的很漂亮
七、analysis 分析作用域
八、runtime 语义处理即翻译php到c++的主流程
eval.cpp Variant eval(LVariableTable *vars, CObjRef self, CStrRef code_str,bool prepend_php /* = true */)
1、php源代码预处理
2、ParseString() 树遍历
3、s->eval(env); 语义分析(递归往下走)
九、函数调用的实现
函数调用基本思路:根据符号表信息,找到object、method、variable等执行环境信息、每次进入一个函数时建立一个thread的栈帧,将php函数调用转化为外部函数的执行逻辑

Reasons for PHPSession failure include configuration errors, cookie issues, and session expiration. 1. Configuration error: Check and set the correct session.save_path. 2.Cookie problem: Make sure the cookie is set correctly. 3.Session expires: Adjust session.gc_maxlifetime value to extend session time.

Methods to debug session problems in PHP include: 1. Check whether the session is started correctly; 2. Verify the delivery of the session ID; 3. Check the storage and reading of session data; 4. Check the server configuration. By outputting session ID and data, viewing session file content, etc., you can effectively diagnose and solve session-related problems.

Multiple calls to session_start() will result in warning messages and possible data overwrites. 1) PHP will issue a warning, prompting that the session has been started. 2) It may cause unexpected overwriting of session data. 3) Use session_status() to check the session status to avoid repeated calls.

Configuring the session lifecycle in PHP can be achieved by setting session.gc_maxlifetime and session.cookie_lifetime. 1) session.gc_maxlifetime controls the survival time of server-side session data, 2) session.cookie_lifetime controls the life cycle of client cookies. When set to 0, the cookie expires when the browser is closed.

The main advantages of using database storage sessions include persistence, scalability, and security. 1. Persistence: Even if the server restarts, the session data can remain unchanged. 2. Scalability: Applicable to distributed systems, ensuring that session data is synchronized between multiple servers. 3. Security: The database provides encrypted storage to protect sensitive information.

Implementing custom session processing in PHP can be done by implementing the SessionHandlerInterface interface. The specific steps include: 1) Creating a class that implements SessionHandlerInterface, such as CustomSessionHandler; 2) Rewriting methods in the interface (such as open, close, read, write, destroy, gc) to define the life cycle and storage method of session data; 3) Register a custom session processor in a PHP script and start the session. This allows data to be stored in media such as MySQL and Redis to improve performance, security and scalability.

SessionID is a mechanism used in web applications to track user session status. 1. It is a randomly generated string used to maintain user's identity information during multiple interactions between the user and the server. 2. The server generates and sends it to the client through cookies or URL parameters to help identify and associate these requests in multiple requests of the user. 3. Generation usually uses random algorithms to ensure uniqueness and unpredictability. 4. In actual development, in-memory databases such as Redis can be used to store session data to improve performance and security.

Managing sessions in stateless environments such as APIs can be achieved by using JWT or cookies. 1. JWT is suitable for statelessness and scalability, but it is large in size when it comes to big data. 2.Cookies are more traditional and easy to implement, but they need to be configured with caution to ensure security.


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