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- const README: rewrite the space-saving claim per issue #5 follow-ups (constant-expression const vs #define immediates; which const qualify as constant expressions) - const README: fix the class-section diagnosis per issue #338 (overload resolution picks the const overload; the restriction only surfaces once that overload is removed) - sizeof README: virtual-inheritance result is compiler-dependent (GCC merges vbptr+vfptr -> 16, MSVC keeps them separate -> 32) #246 - static README: new section on internal linkage / access restriction with anonymous-namespace comparison #142 - 10-day practice: full problem list table + fixed day links #136 - new design_pattern/singleton/singleton_default.hpp: reusable thread-safe CRTP singleton template, compile+concurrency tested #303
83 lines
2.3 KiB
Markdown
83 lines
2.3 KiB
Markdown
> 来自 [C++那些事网站](https://light-city.github.io/stories_things/cpp-projects/cpp-ipc-practice/) 的文章，由站点同步脚本导出。
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# C++ 进程间通信实战
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进程间通信是一个非常重要的话题，特别是像一些大型项目都有它的影子，例如：PostgreSQL使用了管道完成copy的进程间通信，那么本节也将基于这个主题，使用C++去搭建一个进程间通过管道通信的demo出来，本节将会结合前面几节讲的内容，给出一个比较完整的实战例子出来：
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- mutex
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- condition_variable
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- thread
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注：本节的完整代码会放在星球中。
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首先一个很简单的管道用法为：
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- 创建一个管道
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它会creating a pipe, forking, and invoking the shell.
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```cpp
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// FILE *popen(const char *command, const char *type);
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pipe = popen(command.c_str(), "w");
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```
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- 关闭一个管道
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```cpp
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// int pclose(FILE *stream);
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pclose(pipe);
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```
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接下来我们就只需要往里面写与读了，原理也很简单，例如：
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此时便会把data写入到前面创建的管道中。
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```cpp
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// size_t fwrite( const void* buffer, size_t size, size_t count, FILE* stream );
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size_t written = fwrite(data.c_str(), sizeof(char), data.size(), pipe);
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```
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如果从管道中读取，我们可以使用fread或者fgets，`fgets` 会在读取到换行符或达到缓冲区大小时停止，而 `fread` 会尽可能多地读取数据，直到达到指定的字节数或遇到文件结尾。同理，上面的fwrite可以替换为fputs。
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现在，一个管道的基本使用介绍完了，如何写一个完整的demo？
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很简单，我们只需要创建两个线程，一个读，一个写，然后写线程往pipe里面写数据，读线程从pipe里面读即可。
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例如：
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```cpp
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std::thread writer_thread(write_to_pipe);
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std::thread reader_thread(read_from_pipe);
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writer_thread.join();
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reader_thread.join();
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```
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写线程需要做的事情就是调用fwrite丢数据即可
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```cpp
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ProcessWriter writer("cat > /tmp/pipe");
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// 写入数据
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std::string message = "Hello pipe!\n";
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if (!writer.write(message)) {
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std::cerr << "Failed to write data to pipe" << std::endl;
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}
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```
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同理，读线程取数据：
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```cpp
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ProcessReader reader("/tmp/pipe");
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// 读取数据
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std::string message;
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while (reader.read(message)) {
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// do something
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}
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```
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最后的效果就是：
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```cpp
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Read from pipe: Hello pipe!
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``` |