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修复 Emacs 在 macOS 下最大打开文件数为 1024 的问题

  tags: macOS

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不知道从哪个版本开始,macOS 最大文件数(max open files)改成了 1024,这对于使用 lsp 进行开发来说,显得有些小。而且这个问题并不能简单通过调大 ulimit 解决,在这个 reddit 帖子里,rpluim 用户提到:

Emacs uses pselect, which is limited to FD_SETSIZE file descriptors, usually 1024. I suspect you've got one of the file-watching utilities enabled in emacs, which tends to use up a lot of file descriptors.

Increasing the maxfiles limit will not change the value of FD_SETSIZE compiled into emacs and the macOS libraries. Emacs would have to move to using poll or kqueue to fully solve this issue.

在 macOS 的开发者文档里也能找到印证:

The default size FD_SETSIZE (currently 1024) is some-what somewhat what smaller than the current kernel limit to the number of open files. However, in order to accommodate programs which might potentially use a larger number of open files with select, it is possible to increase this size within a program by providing a larger definition of FD_SETSIZE before the inclusion of <sys/types.h>.

但是文档里没提到怎么改,搜了下找到了一个 erlang 的类似问题,里面有提到怎么修改:

CFLAGS="-DFD_SETSIZE=10000 -DDARWIN_UNLIMITED_SELECT"

Great!经过一番测试,成功将 emacs 的最大文件数改成 10000,这里总结下步骤:

  1. 调大系统级别 ulimit 的限制,可参考这个 gistMac OS X下的资源限制。新建文件 limit.maxfiles.plist

    <?xml version="1.0" encoding="UTF-8"?>
    <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN"
         "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
    <plist version="1.0">
    <dict>
     <key>Label</key>
     <string>limit.maxfiles</string>
     <key>ProgramArguments</key>
     <array>
       <string>launchctl</string>
       <string>limit</string>
       <string>maxfiles</string>
       <string>64000</string>
       <string>524288</string>
     </array>
     <key>RunAtLoad</key>
     <true/>
     <key>ServiceIPC</key>
     <false/>
    </dict>
    </plist>

    上面的 xml 含义是把最大文件打开数的 soft/hard 限制分别改成 64000 与 524288。

    sudo chown root:wheel /Library/LaunchDaemons/limit.maxfiles.plist
    sudo chmod 644 /Library/LaunchDaemons/limit.maxfiles.plist
    # 加载plist文件
    sudo launchctl load -w /Library/LaunchDaemons/limit.maxfiles.plist
    # 确认已经生效
    launchctl limit maxfiles
    # 或
    ulimit -n
  2. 从源码编译 Emacs,在 configure 时指定 CFLAGS 参数。参考命令:

    git clone https://git.savannah.gnu.org/emacs && cd emacs
    git checkout emacs-28
    git clean -xf
    
    ./autogen.sh
    ./configure "CFLAGS=-DFD_SETSIZE=10000 -DDARWIN_UNLIMITED_SELECT"
    
    export CPATH=`xcrun --show-sdk-path`/usr/include:`xcrun --show-sdk-path`/usr/include/libxml2
    
    make -j 4 && make install

    这里指定 FD_SETSIZE 为 1w,需要小于 xml 中的 hard 限制。之后打开新编译的 Emacs 进行测试:

    (shell-command-to-string "ulimit -n")
    ;; 10000
    
    (dotimes (i 2000)
    (make-process
    :name (format "Sleep-%s" i)
    :buffer nil
    :command '("sleep" "60000")
    :connection-type 'pipe))

    上面的 dotimes 代码块创建了 2000 个进程,之后用 lsof -p ${emacs_pid} | wc -l 查看打开的文件数,可以看到是 4000 多个,应该是一个 process 会打开两个文件:stdout 与 stderr。

这样,Emacs 最大文件打开数就成功修改了!

签名

如果在启动 Emacs 时,遇到下面的错误:

Killed: 9
Exception Type:  EXC_BAD_ACCESS (SIGKILL (Code Signature Invalid))

可以尝试重新签名

codesign --force --deep --sign - /Applications/Emacs.app/

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