The Waiting Game

A short presentation about the basics of working with processes in Ruby.

Transcript

1. ...
2. The Waiting Game
3. Tim Uruski PetroFeed tim@petrofeed.com
4. • Starting processes basics • Talking to processes • Starting process with libraries
5. Built-in Ways to start a process
6. backticks
7. `whoami`
8. %x(tail #{file})
9. files = `grep -l puts *.rb`
10. files = `grep -l puts *.rb` output command argv
11. • blocks until process ends • captures and returns STDOUT • shared environment • shared STDIN and STDERR
12. $ ruby -e 'puts `cat`.upcase' > hello^D HELLO
13. system
14. system("chmod +x #{file}")
15. passed = system('rake spec')
16. passed = system('rake spec') status command argv
17. • blocks until process ends • returns success; true/false • shared STDIN, STDOUT, STDERR • shared environment
18. $ ruby -e "p system('grep foo') > bar^D false
19. fork
20. if fork puts 'parent' else puts 'child' end
21. • returns "twice" • parent gets a PID • child gets nil
22. fork do puts 'child' end puts 'parent'
23. • child executes block • parent jumps to end of block
24. • complete copy of a process • preload an environment • memory management
25. exec
26. exec('ruby script/rails')
27. • no turning back* • replaces the process • often combined with fork
28. • checks for command first • raises Errno::ENOENT
29. $ ruby -e "exec('date')" Tue 10 Jun 2014 18:15:44 MDT ! $ ruby -e "exec('dte')" -e:1:in `exec': No such file or directory - dte (Errno::ENOENT) ! $ ruby -e "exec('dte') rescue nil or puts 'oops'" oops
30. • shared STDIN, STDOUT, STDERR
31. $ ruby -e "STDOUT.puts STDIN.gets;\ > STDOUT.flush;\ > exec('cat')" > names alice bob ^D $ tail names alice bob
32. • shared environment
33. $ ruby -e "ENV['FOO'] = 'bar';\ > exec('echo \$FOO')" bar
34. spawn
35. spawn('rails server')
36. Process.spawn('rails server')
37. pid = spawn('rails server') command argv
38. pid = spawn('rails' 'server') command argv
39. $ ruby -e "spawn('wc'); Process.wait" hello world yes, this is dog ^D 2 6 29
40. $ ruby -e "spawn('bc'); Process.wait" 1 + 1 2 x = 42 y = 3.14159 x * y 131.94678
41. input_rd, input_wr = IO.pipe output_rd, output_wr = IO.pipe ! spawn('ruby', in: input_rd, out: output_wr) ! input_wr.puts "puts 'hello world'" input_wr.close ! output_wr.close puts output_rd.read #=> 'hello world'
42. input_rd, input_wr = IO.pipe output_rd, output_wr = IO.pipe ! spawn('ruby', in: input_rd, out: output_wr) ! input_wr.puts "puts 'hello world'" input_wr.close ! output_wr.close puts output_rd.read #=> 'hello world'
43. input_rd, input_wr = IO.pipe output_rd, output_wr = IO.pipe ! spawn('ruby', in: input_rd, out: output_wr) ! input_wr.puts "puts 'hello world'" input_wr.close ! output_wr.close puts output_rd.read #=> 'hello world'
44. input_rd, input_wr = IO.pipe output_rd, output_wr = IO.pipe ! spawn('ruby', in: input_rd, out: output_wr) ! input_wr.puts "puts 'hello world'" input_wr.close ! output_wr.close puts output_rd.read #=> 'hello world'
45. input_rd, input_wr = IO.pipe output_rd, output_wr = IO.pipe ! spawn('ruby', in: input_rd, out: output_wr) ! input_wr.puts "puts 'hello world'" input_wr.close ! output_wr.close puts output_rd.read #=> 'hello world'
46. input_rd, input_wr = IO.pipe output_rd, output_wr = IO.pipe ! spawn('ruby', in: input_rd, out: output_wr) ! input_wr.puts "puts 'hello world'" input_wr.close ! output_wr.close puts output_rd.read #=> 'hello world'
47. input_rd, input_wr = IO.pipe output_rd, output_wr = IO.pipe ! spawn('ruby', in: input_rd, out: output_wr) ! input_wr.puts "puts 'hello world'" input_wr.close ! output_wr.close puts output_rd.read #=> 'hello world'
48. Command write read write read Pipe A Pipe B in out
49. # plumbing
50. IO.popen
51. IO.popen('ruby', 'w+') do |io| io.puts "puts 'hello world'" io.close_write puts io.read end
52. io = IO.popen('ruby', 'w+') ! io.puts "puts 'hello world'" io.close_write puts io.read
53. Command write read write read Pipe A Pipe B IO.popen
54. Talking to Processes
55. wait
56. Waits for a process to finish. Blocks your program.
57. Process.wait(123) Process.waitpid(123) #=> returns status
58. Process.wait2(123) Process.waitpid2(123) #=> returns [pid, status]
59. Process.waitall #=> returns list of pids
60. detach
61. Process.detatch(123)
62. kill
63. Sends a signal
64. Process.kill('INT', 123) Process.kill('SIGINT', 234) Process.kill(:TERM, 345) Process.kill(9, 456)
65. $ man signal
66. 1 SIGHUP terminate process terminal line hangup 2 SIGINT terminate process interrupt program 3 SIGQUIT create core image quit program 4 SIGILL create core image illegal instruction 5 SIGTRAP create core image trace trap 6 SIGABRT create core image abort program (formerly SIGIOT) 7 SIGEMT create core image emulate instruction executed 8 SIGFPE create core image floating-point exception 9 SIGKILL terminate process kill program 10 SIGBUS create core image bus error 11 SIGSEGV create core image segmentation violation 12 SIGSYS create core image non-existent system call invoked 13 SIGPIPE terminate process write on a pipe with no reader 14 SIGALRM terminate process real-time timer expired 15 SIGTERM terminate process software termination signal 16 SIGURG discard signal urgent condition present on socket 17 SIGSTOP stop process stop (cannot be caught or ignored) 18 SIGTSTP stop process stop signal generated from keyboard 19 SIGCONT discard signal continue after stop 20 SIGCHLD discard signal child status has changed 21 SIGTTIN stop process background read attempted from control terminal 22 SIGTTOU stop process background write attempted to control terminal 23 SIGIO discard signal I/O is possible on a descriptor (see fcntl(2)) 24 SIGXCPU terminate process cpu time limit exceeded (see setrlimit(2)) 25 SIGXFSZ terminate process file size limit exceeded (see setrlimit(2)) 26 SIGVTALRM terminate process virtual time alarm (see setitimer(2)) 27 SIGPROF terminate process profiling timer alarm (see setitimer(2)) 28 SIGWINCH discard signal Window size change 29 SIGINFO discard signal status request from keyboard 30 SIGUSR1 terminate process User defined signal 1 31 SIGUSR2 terminate process User defined signal 2
67. $?
68. system('false') and $? => #<Process::Status: pid 88459 exit 1> ! system('true') and $? => #<Process::Status: pid 88467 exit 0>
69. Extended Library ways to start a process
70. Open3
71. require 'open3' ! Open3.popen3('cat') do |stdin, stdout, stderr| stdin.puts 'hello' stdin.close puts stdout.read end
72. PTY
73. Pseudo terminals are used for...
74. Shell
75. require 'shell' ! Shell.def_system_command 'find', '/bin/find' ! sh = Shell.new files = sh.transact do find '.', '-name *.rb' end
76. require 'shell' ! Shell.def_system_command 'find', '/bin/find' ! sh = Shell.new files = sh.transact do find '.', '-name *.rb' end
77. require 'shell' ! Shell.def_system_command 'find', '/bin/find' ! sh = Shell.new files = sh.transact do find '.', '-name *.rb' end
78. require 'shell' ! Shell.def_system_command 'find', '/bin/find' ! sh = Shell.new files = sh.transact do find '.', '-name *.rb' end
79. Buggy, undocumented and not in active development. Too bad.
80. # Process Basics - backticks - system - fork - exec - spawn - IO.popen
81. # Process Communication - pids - stdio - signals
82. # Extended Library - Open3 - PTY - Shell
83. • IO blocking and buffering • process groups and sessions • working directories • permissions and umasks • process resource limiting • demonizing a process • pseudo-terminals
84. Next Time Usage Examples Maybe
85. Thank You