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使用strace查找Emacs啟動阻塞的原因

作者：Darksun
系統(tǒng) Linux
之前就覺得我的 Emacs 啟動好慢，查看啟動日志會發(fā)現(xiàn)啟動到一般的時候會有一個比較長時間的卡頓。 之前一直沒有理會它，今天花了點時間探索了一下，發(fā)現(xiàn)罪魁禍?zhǔn)拙尤皇?exec-path-from-shell 這個包。

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之前就覺得我的 Emacs 啟動好慢，查看啟動日志會發(fā)現(xiàn)啟動到一般的時候會有一個比較長時間的卡頓。 之前一直沒有理會它，今天花了點時間探索了一下，發(fā)現(xiàn)罪魁禍?zhǔn)拙尤皇?exec-path-from-shell 這個包。

現(xiàn)將探索的過程記錄如下： 由于使用了 spacemacs 的配置，配置上比較復(fù)雜，不太想通過實驗縮減配置的方式來摸索出問題的地方。剛好最近在學(xué)習(xí)使用 strace 工具，因此決定使用 strace 來看看 Emacs 到底卡在哪里。

strace emacs --fg-daemon

輸出的內(nèi)容特別多，這里只截取卡頓前的部分內(nèi)容

  1. readlinkat(AT_FDCWD, "/home", 0x7ffd1d3abb50, 1024) = -1 EINVAL (無效的參數(shù))
  2. readlinkat(AT_FDCWD, "/home/lujun9972", 0x7ffd1d3abf00, 1024) = -1 EINVAL (無效的參數(shù))
  3. readlinkat(AT_FDCWD, "/home/lujun9972/.emacs.d", 0x7ffd1d3ac2b0, 1024) = -1 EINVAL (無效的參數(shù))
  4. readlinkat(AT_FDCWD, "/home/lujun9972/.emacs.d/elpa", 0x7ffd1d3ac660, 1024) = -1 EINVAL (無效的參數(shù))
  5. readlinkat(AT_FDCWD, "/home/lujun9972/.emacs.d/elpa/exec-path-from-shell-20180323.1904", 0x7ffd1d3aca10, 1024) = -1 EINVAL (無效的參數(shù))
  6. readlinkat(AT_FDCWD, "/home/lujun9972/.emacs.d/elpa/exec-path-from-shell-20180323.1904/exec-path-from-shell.elc", 0x7ffd1d3acdc0, 1024) = -1 EINVAL (無效的參數(shù))
  7. lseek(7, -2655, SEEK_CUR)               = 1441
  8. read(7, "\n(defvar exec-path-from-shell-de"..., 4096) = 4096
  9. lseek(7, 5537, SEEK_SET)                = 5537
  10. lseek(7, 5537, SEEK_SET)                = 5537
  11. lseek(7, 5537, SEEK_SET)                = 5537
  12. lseek(7, 5537, SEEK_SET)                = 5537
  13. lseek(7, 5537, SEEK_SET)                = 5537
  14. lseek(7, 5537, SEEK_SET)                = 5537
  15. brk(0x7507000)                          = 0x7507000
  16. lseek(7, 5537, SEEK_SET)                = 5537
  17. lseek(7, 5537, SEEK_SET)                = 5537
  18. lseek(7, 5537, SEEK_SET)                = 5537
  19. read(7, "230\\205\26\0\t\22\\307\\310\t!\vC\\\"\\211\24\\2"..., 4096) = 2430
  20. lseek(7, 7967, SEEK_SET)                = 7967
  21. lseek(7, 7967, SEEK_SET)                = 7967
  22. lseek(7, 7967, SEEK_SET)                = 7967
  23. lseek(7, 7967, SEEK_SET)                = 7967
  24. read(7, "", 4096)                       = 0
  25. close(7)                                = 0
  26. getpid()                                = 10818
  27. faccessat(AT_FDCWD, "/home/lujun9972/bin/printf", X_OK) = -1 ENOENT (沒有那個文件或目錄)
  28. faccessat(AT_FDCWD, "/usr/local/sbin/printf", X_OK) = -1 ENOENT (沒有那個文件或目錄)
  29. faccessat(AT_FDCWD, "/usr/local/bin/printf", X_OK) = -1 ENOENT (沒有那個文件或目錄)
  30. faccessat(AT_FDCWD, "/usr/bin/printf", X_OK) = 0
  31. stat("/usr/bin/printf", {st_mode=S_IFREG|0755, st_size=51176, ...}) = 0
  32. openat(AT_FDCWD, "/dev/null", O_RDONLY|O_CLOEXEC) = 7
  33. faccessat(AT_FDCWD, "/proc/5070/fd/.", F_OK) = 0
  34. faccessat(AT_FDCWD, "/proc/5070/fd/.", F_OK) = 0
  35. faccessat(AT_FDCWD, "/bin/bash", X_OK)  = 0
  36. stat("/bin/bash", {st_mode=S_IFREG|0755, st_size=903440, ...}) = 0
  37. pipe2([8, 9], O_CLOEXEC)                = 0
  38. rt_sigprocmask(SIG_BLOCK, [INT CHLD], [], 8) = 0
  39. vfork()                                 = 10949
  40. rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
  41. close(9)                                = 0
  42. close(7)                                = 0
  43. read(8, "bash: \346\227\240\346\263\225\350\256\276\345\256\232\347\273\210\347\253\257\350\277\233\347\250\213\347\273"..., 16384) = 74
  44. read(8, "bash: \346\255\244 shell \344\270\255\346\227\240\344\273\273\345\212\241\346\216\247\345"..., 16310) = 35
  45. read(8, "setterm: \347\273\210\347\253\257 xterm-256color \344"..., 16275) = 51
  46. read(8, "Couldn't get a file descriptor r"..., 16224) = 56
  47. read(8, "bash: [: \357\274\232\351\234\200\350\246\201\346\225\264\346\225\260\350\241\250\350\276\276\345\274"..., 16168) = 34
  48. read(8, "Your display number is 0\n", 16134) = 25
  49. read(8, "Test whether fcitx is running co"..., 16109) = 53
  50. read(8, "Fcitx is running correctly.\n\n==="..., 16056) = 87
  51. read(8, "Launch fbterm...\n", 15969)    = 17
  52. read(8, "stdin isn't a tty!\n", 15952)  = 19
  53. read(8, "__RESULT\0/home/lujun9972/bin:/ho"..., 15933) = 298
  54. read(8, 0x7ffd1d39ce9d, 15635)          = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
  55. --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=10949, si_uid=1000, si_status=0, si_utime=10, si_stime=7} ---
  56. rt_sigreturn({mask=[]})                 = -1 EINTR (被中斷的系統(tǒng)調(diào)用)
  57. read(8, "", 15635)                      = 0
  58. wait4(10949, [{WIFEXITED(s) && WEXITSTATUS(s) == 0}], 0, NULL) = 10949
  59. close(8)                                = 0
  60. getpid()                                = 10818
  61. faccessat(AT_FDCWD, "/home/lujun9972/bin/printf", X_OK) = -1 ENOENT (沒有那個文件或目錄)
  62. faccessat(AT_FDCWD, "/usr/local/sbin/printf", X_OK) = -1 ENOENT (沒有那個文件或目錄)
  63. faccessat(AT_FDCWD, "/usr/local/bin/printf", X_OK) = -1 ENOENT (沒有那個文件或目錄)
  64. faccessat(AT_FDCWD, "/usr/bin/printf", X_OK) = 0
  65. stat("/usr/bin/printf", {st_mode=S_IFREG|0755, st_size=51176, ...}) = 0
  66. openat(AT_FDCWD, "/dev/null", O_RDONLY|O_CLOEXEC) = 7
  67. faccessat(AT_FDCWD, "/proc/5070/fd/.", F_OK) = 0
  68. faccessat(AT_FDCWD, "/proc/5070/fd/.", F_OK) = 0
  69. faccessat(AT_FDCWD, "/bin/bash", X_OK)  = 0
  70. stat("/bin/bash", {st_mode=S_IFREG|0755, st_size=903440, ...}) = 0
  71. pipe2([8, 9], O_CLOEXEC)                = 0
  72. rt_sigprocmask(SIG_BLOCK, [INT CHLD], [], 8) = 0
  73. vfork()                                 = 11679
  74. rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
  75. close(9)                                = 0
  76. close(7)                                = 0
  77. read(8, "setterm: \347\273\210\347\253\257 xterm-256color \344"..., 16384) = 51
  78. read(8, "Couldn't get a file descriptor r"..., 16333) = 56
  79. read(8, "/home/lujun9972/.bash_profile: \347"..., 16277) = 72
  80. read(8, "Your display number is 0\nTest wh"..., 16205) = 78
  81. read(8, "Fcitx is running correctly.\n\n==="..., 16127) = 104
  82. read(8, "stdin isn't a tty!\n", 16023)  = 19
  83. read(8, "__RESULT\0b269cd09e7ec4e8a115188c"..., 16004) = 298
  84. read(8, 0x7ffd1d39cba6, 15706)          = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
  85. --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=11679, si_uid=1000, si_status=0, si_utime=1, si_stime=1} ---
  86. rt_sigreturn({mask=[]})                 = -1 EINTR (被中斷的系統(tǒng)調(diào)用)
  87. read(8,

很容易就可以看出，當(dāng) Emacs 卡頓時，它在嘗試從 8 號文件句柄中讀取內(nèi)容。

那么 8 號文件句柄在哪里定義的呢？往前看可以看到：

  1. pipe2([8, 9], O_CLOEXEC)                = 0
  2. rt_sigprocmask(SIG_BLOCK, [INT CHLD], [], 8) = 0
  3. vfork()                                 = 11679
  4. rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
  5. close(9)                                = 0

可以推測出，Emacs 主進(jìn)程 fork 出一個子進(jìn)程（進(jìn)程號為 11679），并通過管道讀取子進(jìn)程的內(nèi)容。

然而，從

  1. --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=11679, si_uid=1000, si_status=0, si_utime=1, si_stime=1} ---
  2. rt_sigreturn({mask=[]})                 = -1 EINTR (被中斷的系統(tǒng)調(diào)用)
  3. read(8,

可以看出，實際上子進(jìn)程已經(jīng)退出了（父進(jìn)程收到 SIGCHLD 信號），父進(jìn)程確依然在嘗試從管道中讀取內(nèi)容，導(dǎo)致的阻塞。

而且從

  1. read(8, "setterm: \347\273\210\347\253\257 xterm-256color \344"..., 16384) = 51
  2. read(8, "Couldn't get a file descriptor r"..., 16333) = 56
  3. read(8, "/home/lujun9972/.bash_profile: \347"..., 16277) = 72
  4. read(8, "Your display number is 0\nTest wh"..., 16205) = 78
  5. read(8, "Fcitx is running correctly.\n\n==="..., 16127) = 104
  6. read(8, "stdin isn't a tty!\n", 16023)  = 19
  7. read(8, "__RESULT\0b269cd09e7ec4e8a115188c"..., 16004) = 298
  8. read(8, 0x7ffd1d39cba6, 15706)          = ? ERESTARTSYS (To be restarted if SA_RESTART is set)

看到，子進(jìn)程的輸出似乎是我的交互式登錄 bash 啟動時的輸出（加載了 .bash_profile）

在往前翻發(fā)現(xiàn)這么一段信息：

  1. readlinkat(AT_FDCWD, "/home", 0x7ffd1d3abb50, 1024) = -1 EINVAL (無效的參數(shù))
  2. readlinkat(AT_FDCWD, "/home/lujun9972", 0x7ffd1d3abf00, 1024) = -1 EINVAL (無效的參數(shù))
  3. readlinkat(AT_FDCWD, "/home/lujun9972/.emacs.d", 0x7ffd1d3ac2b0, 1024) = -1 EINVAL (無效的參數(shù))
  4. readlinkat(AT_FDCWD, "/home/lujun9972/.emacs.d/elpa", 0x7ffd1d3ac660, 1024) = -1 EINVAL (無效的參數(shù))
  5. readlinkat(AT_FDCWD, "/home/lujun9972/.emacs.d/elpa/exec-path-from-shell-20180323.1904", 0x7ffd1d3aca10, 1024) = -1 EINVAL (無效的參數(shù))
  6. readlinkat(AT_FDCWD, "/home/lujun9972/.emacs.d/elpa/exec-path-from-shell-20180323.1904/exec-path-from-shell.elc", 0x7ffd1d3acdc0, 1024) = -1 EINVAL (無效的參數(shù))
  7. lseek(7, -2655, SEEK_CUR)               = 1441
  8. read(7, "\n(defvar exec-path-from-shell-de"..., 4096) = 4096

這很明顯是跟 exec-path-from-shell 有關(guān)啊。

通過查看 exec-path-from-shell 的實現(xiàn)，發(fā)現(xiàn) exec-path-from-shell 的實現(xiàn)原理是通過實際調(diào)啟一個 shell，然后輸出 PATH 和 MANPATH 的值的。 而且對于 bash 來說，默認(rèn)的啟動參數(shù)為 -i -l（可以通過exec-path-from-shell-arguments來設(shè)置）。也就是說 bash 會作為交互式的登錄shell來啟動的，因此會加載 .bash_profile 和 .bashrc。

既然發(fā)現(xiàn)跟 exec-path-from-shell 這個包有關(guān)，而且據(jù)說這個包對 Linux 其實意義不大，那不如直接禁用掉好了。

  1. dotspacemacs-excluded-packages '(exec-path-from-shell) 

再次重啟Emacs，發(fā)現(xiàn)這次啟動速度明顯快了許多了。

 

責(zé)任編輯：龐桂玉 來源： Linux中國
straceEmacsLinux
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