Windows で fork() に最も近いものは何ですか? 質問する

シグウィンWindows では fork() が完全に機能します。したがって、Cygwin の使用が許容される場合、パフォーマンスが問題にならない場合は問題は解決されます。

そうでなければ、Cygwinがfork()をどのように実装しているかを見てください。かなり古いCygwinのアーキテクチャからドキュメント:

5.6. プロセスの作成 Cygwin の fork 呼び出しは、Win32 API の上にうまくマップされないため、特に興味深いものです。このため、正しく実装することが非常に困難です。現在、Cygwin の fork は、初期の UNIX に存在していたものと同様の、非コピーオンライト実装です。

The first thing that happens when a parent process forks a child process is that the parent initializes a space in the Cygwin process table for the child. It then creates a suspended child process using the Win32 CreateProcess call. Next, the parent process calls setjmp to save its own context and sets a pointer to this in a Cygwin shared memory area (shared among all Cygwin tasks). It then fills in the child's .data and .bss sections by copying from its own address space into the suspended child's address space. After the child's address space is initialized, the child is run while the parent waits on a mutex. The child discovers it has been forked and longjumps using the saved jump buffer. The child then sets the mutex the parent is waiting on and blocks on another mutex. This is the signal for the parent to copy its stack and heap into the child, after which it releases the mutex the child is waiting on and returns from the fork call. Finally, the child wakes from blocking on the last mutex, recreates any memory-mapped areas passed to it via the shared area, and returns from fork itself.

While we have some ideas as to how to speed up our fork implementation by reducing the number of context switches between the parent and child process, fork will almost certainly always be inefficient under Win32. Fortunately, in most circumstances the spawn family of calls provided by Cygwin can be substituted for a fork/exec pair with only a little effort. These calls map cleanly on top of the Win32 API. As a result, they are much more efficient. Changing the compiler's driver program to call spawn instead of fork was a trivial change and increased compilation speeds by twenty to thirty percent in our tests.

However, spawn and exec present their own set of difficulties. Because there is no way to do an actual exec under Win32, Cygwin has to invent its own Process IDs (PIDs). As a result, when a process performs multiple exec calls, there will be multiple Windows PIDs associated with a single Cygwin PID. In some cases, stubs of each of these Win32 processes may linger, waiting for their exec'd Cygwin process to exit.

Sounds like a lot of work, doesn't it? And yes, it is slooooow.

EDIT: the doc is outdated, please see this excellent answer for an update