Threaded Awesome

1. Threaded Awesome (that’s an oxymoron) Joe Damato and Aman Gupta

2. About Joe Damato From NJ, Godfather II is actually my Biography CMU/VMWare alum http://timetobleed.com @joedamato

3. About Aman Gupta EventMachine, amqp Ruby Hero 2009 github.com/tmm1 @tmm1

4. What is a thread? source: wikipedia

5. What is a thread?

6. What is a thread? A thread is just a set of execution state

7. What is a thread? A thread is just a set of execution state This state usually includes:

8. What is a thread? A thread is just a set of execution state This state usually includes: instruction & stack pointers

9. What is a thread? A thread is just a set of execution state This state usually includes: instruction & stack pointers scheduling priority

10. What is a thread? A thread is just a set of execution state This state usually includes: instruction & stack pointers scheduling priority other CPU state

11. Threading Models Green threads (1:N) Native Threads (1:1) Hybrid (M:N)

12. Green Threads (1:N)

13. Green Threads (1:N) “Green” because they are light weight

14. Green Threads (1:N) “Green” because they are light weight Kernel doesn’t know they exist

15. Green Threads (1:N) “Green” because they are light weight Kernel doesn’t know they exist Implementation is in userland

16. Green Threads (1:N) “Green” because they are light weight Kernel doesn’t know they exist Implementation is in userland Pros

17. Green Threads (1:N) “Green” because they are light weight Kernel doesn’t know they exist Implementation is in userland Pros Create lots of them cheaply (10,000s)

18. Green Threads (1:N) “Green” because they are light weight Kernel doesn’t know they exist Implementation is in userland Pros Create lots of them cheaply (10,000s) Switch between them cheaply (Ruby doesn’t)

19. Green Threads (1:N) “Green” because they are light weight Kernel doesn’t know they exist Implementation is in userland Pros Create lots of them cheaply (10,000s) Switch between them cheaply (Ruby doesn’t) Schedule them however you want

20. Green Threads (1:N) “Green” because they are light weight Kernel doesn’t know they exist Implementation is in userland Pros Create lots of them cheaply (10,000s) Switch between them cheaply (Ruby doesn’t) Schedule them however you want Cons

21. Green Threads (1:N) “Green” because they are light weight Kernel doesn’t know they exist Implementation is in userland Pros Create lots of them cheaply (10,000s) Switch between them cheaply (Ruby doesn’t) Schedule them however you want Cons A blocking call in one blocks ALL

22. Green Threads (1:N) “Green” because they are light weight Kernel doesn’t know they exist Implementation is in userland Pros Create lots of them cheaply (10,000s) Switch between them cheaply (Ruby doesn’t) Schedule them however you want Cons A blocking call in one blocks ALL Kernel doesn’t know about them

23. Green Threads (1:N) “Green” because they are light weight Kernel doesn’t know they exist Implementation is in userland Pros Create lots of them cheaply (10,000s) Switch between them cheaply (Ruby doesn’t) Schedule them however you want Cons A blocking call in one blocks ALL Kernel doesn’t know about them Can’t take advantage of SMP

24. Green Threads (1:N) (pics or it didn’t happen)

25. Ruby 1.8 uses Green Threads (and does it wrong)

26. Native Threads (1:1)

27. Native Threads (1:1) Native Threads

28. Native Threads (1:1) Native Threads Kernel knows they exist

29. Native Threads (1:1) Native Threads Kernel knows they exist Some userland code (libpthread)

30. Native Threads (1:1) Native Threads Kernel knows they exist Some userland code (libpthread) Pros

31. Native Threads (1:1) Native Threads Kernel knows they exist Some userland code (libpthread) Pros Take advantage of SMP

32. Native Threads (1:1) Native Threads Kernel knows they exist Some userland code (libpthread) Pros Take advantage of SMP Shared memory

33. Native Threads (1:1) Native Threads Kernel knows they exist Some userland code (libpthread) Pros Take advantage of SMP Shared memory Blocking in one thread doesn’t block everyone

34. Native Threads (1:1) Native Threads Kernel knows they exist Some userland code (libpthread) Pros Take advantage of SMP Shared memory Blocking in one thread doesn’t block everyone Don’t have to write a scheduler

35. Native Threads (1:1) Native Threads Kernel knows they exist Some userland code (libpthread) Pros Take advantage of SMP Shared memory Blocking in one thread doesn’t block everyone Don’t have to write a scheduler Cons

36. Native Threads (1:1) Native Threads Kernel knows they exist Some userland code (libpthread) Pros Take advantage of SMP Shared memory Blocking in one thread doesn’t block everyone Don’t have to write a scheduler Cons Overhead limits how many you can create

37. Native Threads (1:1) Native Threads Kernel knows they exist Some userland code (libpthread) Pros Take advantage of SMP Shared memory Blocking in one thread doesn’t block everyone Don’t have to write a scheduler Cons Overhead limits how many you can create Bugs (glibc, more threads = slower creation time)

38. Native Threads (1:1) Native Threads Kernel knows they exist Some userland code (libpthread) Pros Take advantage of SMP Shared memory Blocking in one thread doesn’t block everyone Don’t have to write a scheduler Cons Overhead limits how many you can create Bugs (glibc, more threads = slower creation time) Don’t have fine grained scheduling control

39. Native Threads (1:1)

40. Ruby 1.9 uses Native Threads (but.. they don’t execute in parallel)

41. Hybrid Threads (M:N)

42. Hybrid Threads (M:N) Hybrid threads

43. Hybrid Threads (M:N) Hybrid threads Almost best of both worlds

44. Hybrid Threads (M:N) Hybrid threads Almost best of both worlds Pros

45. Hybrid Threads (M:N) Hybrid threads Almost best of both worlds Pros Take advantage of SMP

46. Hybrid Threads (M:N) Hybrid threads Almost best of both worlds Pros Take advantage of SMP Cheap setup and teardown

47. Hybrid Threads (M:N) Hybrid threads Almost best of both worlds Pros Take advantage of SMP Cheap setup and teardown Blocking in one thread doesn’t block everyone

48. Hybrid Threads (M:N) Hybrid threads Almost best of both worlds Pros Take advantage of SMP Cheap setup and teardown Blocking in one thread doesn’t block everyone Cons

49. Hybrid Threads (M:N) Hybrid threads Almost best of both worlds Pros Take advantage of SMP Cheap setup and teardown Blocking in one thread doesn’t block everyone Cons Need 2 schedulers (userland + kernel)

50. Hybrid Threads (M:N) Hybrid threads Almost best of both worlds Pros Take advantage of SMP Cheap setup and teardown Blocking in one thread doesn’t block everyone Cons Need 2 schedulers (userland + kernel) Need to make them actually work together

51. Hybrid Threads (M:N) Hybrid threads Almost best of both worlds Pros Take advantage of SMP Cheap setup and teardown Blocking in one thread doesn’t block everyone Cons Need 2 schedulers (userland + kernel) Need to make them actually work together All green threads backed by same native thread can be blocked

52. Hybrid Threads (M:N)

53. Erlang uses Hybrid Threads Ruby 1.9, too (with fibers)

54. Multitasking Types Preemptive Multitasking Cooperative Multitasking

55. Preemptive Multitasking

56. Preemptive Multitasking Outside event (timer) signals end of CPU slice

57. Preemptive Multitasking Outside event (timer) signals end of CPU slice Handle important events quickly

58. Preemptive Multitasking Outside event (timer) signals end of CPU slice Handle important events quickly Can help ensure everyone gets to execute

59. Preemptive Multitasking Outside event (timer) signals end of CPU slice Handle important events quickly Can help ensure everyone gets to execute But..

60. Preemptive Multitasking Outside event (timer) signals end of CPU slice Handle important events quickly Can help ensure everyone gets to execute But.. Need to build a smart scheduler

61. Preemptive Multitasking Outside event (timer) signals end of CPU slice Handle important events quickly Can help ensure everyone gets to execute But.. Need to build a smart scheduler Can yield non-determistic execution order

62. Cooperative Multitasking

63. Cooperative Multitasking Threads voluntarily release the CPU

64. Cooperative Multitasking Threads voluntarily release the CPU Give up the CPU when it is “optimal”

65. Cooperative Multitasking Threads voluntarily release the CPU Give up the CPU when it is “optimal” Can guarantee deterministic execution order

66. Cooperative Multitasking Threads voluntarily release the CPU Give up the CPU when it is “optimal” Can guarantee deterministic execution order Very simple “scheduler”

67. Cooperative Multitasking Threads voluntarily release the CPU Give up the CPU when it is “optimal” Can guarantee deterministic execution order Very simple “scheduler” But..

68. Cooperative Multitasking Threads voluntarily release the CPU Give up the CPU when it is “optimal” Can guarantee deterministic execution order Very simple “scheduler” But.. Badly written code can hang all threads

69. So, what is a fiber? In Ruby fibers are green threads with cooperative multitasking.

70. So what’s the deal with ruby threads? strace google-perftools ltrace gdb

71. strace trace system calls and signals strace -cp <pid> strace -ttTp <pid> -o <file>

72. strace -cp <pid> -c Count time, calls, and errors for each system call and report a summary on program exit. -p pid Attach to the process with the process ID pid and begin tracing. % time seconds usecs/call calls errors syscall ------ ----------- ----------- --------- --------- ---------------- 50.39 0.000064 0 1197 592 read 34.65 0.000044 0 609 writev 14.96 0.000019 0 1226 epoll_ctl 0.00 0.000000 0 4 close 0.00 0.000000 0 1 select 0.00 0.000000 0 4 socket 0.00 0.000000 0 4 4 connect 0.00 0.000000 0 1057 epoll_wait ------ ----------- ----------- --------- --------- ---------------- 100.00 0.000127 4134 596 total

73. strace -ttTp <pid> -o <file> -t Prefix each line of the trace with the time of day. -tt If given twice, the time printed will include the microseconds. -T Show the time spent in system calls. This records the time difference between the beginning and the end of each system call. -o filename Write the trace output to the file filename rather than to stderr. 01:09:11.266949 epoll_wait(9, {{EPOLLIN, {u32=68841296, u64=68841296}}}, 4096, 50) = 1 <0.033109> 01:09:11.300102 accept(10, {sa_family=AF_INET, sin_port=38313, sin_addr="127.0.0.1"}, [1226]) = 22 <0.000014> 01:09:11.300190 fcntl(22, F_GETFL) = 0x2 (flags O_RDWR) <0.000007> 01:09:11.300237 fcntl(22, F_SETFL, O_RDWR|O_NONBLOCK) = 0 <0.000008> 01:09:11.300277 setsockopt(22, SOL_TCP, TCP_NODELAY, [1], 4) = 0 <0.000008> 01:09:11.300489 accept(10, 0x7fff5d9c07d0, [1226]) = -1 EAGAIN <0.000014> 01:09:11.300547 epoll_ctl(9, EPOLL_CTL_ADD, 22, {EPOLLIN, {u32=108750368, u64=108750368}}) = 0 <0.000009> 01:09:11.300593 epoll_wait(9, {{EPOLLIN, {u32=108750368, u64=108750368}}}, 4096, 50) = 1 <0.000007> 01:09:11.300633 read(22, "GET / HTTP/1.1r"..., 16384) = 772 <0.000012> 01:09:11.301727 rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0 <0.000007> 01:09:11.302095 poll([{fd=5, events=POLLIN|POLLPRI}], 1, 0) = 0 (Timeout) <0.000008> 01:09:11.302144 write(5, "1000000-0003SELECT * FROM `table`"..., 56) = 56 <0.000023> 01:09:11.302221 read(5, "25101,20x234m"..., 16384) = 284 <1.300897>

77. Let’s strace ruby..

78. Let’s strace ruby.. 15:45:51.658164 --- SIGVTALRM (Virtual timer expired) @ 0 (0) --- 15:45:51.658244 rt_sigreturn(0x1a) = 2207807 <0.000009> 15:45:51.678208 --- SIGVTALRM (Virtual timer expired) @ 0 (0) --- 15:45:51.678271 rt_sigreturn(0x1a) = 0 <0.000009> 15:45:51.698161 --- SIGVTALRM (Virtual timer expired) @ 0 (0) --- 15:45:51.698216 rt_sigreturn(0x1a) = 140734552062624 <0.000009> 15:45:51.718154 --- SIGVTALRM (Virtual timer expired) @ 0 (0) --- 15:45:51.718192 rt_sigreturn(0x1a) = 140734552066688 <0.000009> 15:45:51.738185 --- SIGVTALRM (Virtual timer expired) @ 0 (0) --- 15:45:51.738221 rt_sigreturn(0x1a) = 11333952 <0.000008> 15:45:51.758162 --- SIGVTALRM (Virtual timer expired) @ 0 (0) --- 15:45:51.758216 rt_sigreturn(0x1a) = 0 <0.000009> 15:45:51.778223 --- SIGVTALRM (Virtual timer expired) @ 0 (0) --- 15:45:51.778296 rt_sigreturn(0x1a) = 0 <0.000009> 15:45:51.798170 --- SIGVTALRM (Virtual timer expired) @ 0 (0) --- 15:45:51.798244 rt_sigreturn(0x1a) = 2298980 <0.000009> 15:45:51.818168 --- SIGVTALRM (Virtual timer expired) @ 0 (0) --- 15:45:51.819817 rt_sigreturn(0x1a) = 1 <0.000010> 15:45:51.838196 --- SIGVTALRM (Virtual timer expired) @ 0 (0) ---

79. Let’s strace ruby.. 15:45:51.658164 --- SIGVTALRM (Virtual timer expired) @ 0 (0) --- 15:45:51.658244 rt_sigreturn(0x1a) = 2207807 <0.000009> 15:45:51.678208 --- SIGVTALRM (Virtual timer expired) @ 0 (0) --- 15:45:51.678271 rt_sigreturn(0x1a) = 0 <0.000009> 15:45:51.698161 --- SIGVTALRM (Virtual timer expired) @ 0 (0) --- 15:45:51.698216 rt_sigreturn(0x1a) = 140734552062624 <0.000009> 15:45:51.718154 --- SIGVTALRM (Virtual timer expired) @ 0 (0) --- 15:45:51.718192 rt_sigreturn(0x1a) = 140734552066688 <0.000009> 15:45:51.738185 --- SIGVTALRM (Virtual timer expired) @ 0 (0) --- 15:45:51.738221 rt_sigreturn(0x1a) = 11333952 <0.000008> 15:45:51.758162 --- SIGVTALRM (Virtual timer expired) @ 0 (0) --- 15:45:51.758216 rt_sigreturn(0x1a) = 0 <0.000009> 15:45:51.778223 --- SIGVTALRM (Virtual timer expired) @ 0 (0) --- 15:45:51.778296 rt_sigreturn(0x1a) = 0 <0.000009> 15:45:51.798170 --- SIGVTALRM (Virtual timer expired) @ 0 (0) --- 15:45:51.798244 rt_sigreturn(0x1a) = 2298980 <0.000009> 15:45:51.818168 --- SIGVTALRM (Virtual timer expired) @ 0 (0) --- 15:45:51.819817 rt_sigreturn(0x1a) = 1 <0.000010> 15:45:51.838196 --- SIGVTALRM (Virtual timer expired) @ 0 (0) --- wtf is SIGVTALRM?

80. ruby uses setitimer and signals to schedule green threads* The first time a new thread is created, ruby calls: setitimer(ITIMER_VIRTUAL, 10ms): tell the kernel to send the process a SIGVTALRM every 10ms posix_signal(SIGVTALRM, catch_timer): bind the catch_timer function to the signal * when compiled without --enable-pthread

81. static void catch_timer(sig) int sig; { if (!rb_thread_critical) { static VALUE rb_thread_pending = 1; rb_thread_start_0(fn, arg, th) } VALUE (*fn)(); /* cause EINTR */ void *arg; } rb_thread_t th; { void if (!thread_init) { rb_thread_start_timer() thread_init = 1; { posix_signal(SIGVTALRM, catch_timer); struct itimerval tval; rb_thread_start_timer(); } if (!thread_init) return; tval.it_interval.tv_sec = 0; /* ... */ tval.it_interval.tv_usec = 10000; } tval.it_value = tval.it_interval; setitimer(ITIMER_VIRTUAL, &tval, NULL); }

84. static void catch_timer(sig) int sig; { if (!rb_thread_critical) { static VALUE rb_thread_pending = 1; rb_thread_start_0(fn, arg, th) } VALUE (*fn)(); /* cause EINTR */ void *arg; } rb_thread_t th; { void if (!thread_init) { rb_thread_start_timer() thread_init = 1; { posix_signal(SIGVTALRM, catch_timer); struct itimerval tval; rb_thread_start_timer(); } if (!thread_init) return; tval.it_interval.tv_sec = 0; /* ... */ tval.it_interval.tv_usec = 10000; } tval.it_value = tval.it_interval; setitimer(ITIMER_VIRTUAL, &tval, NULL); } strace -e trace=setitimer ruby threaded.rb setitimer(ITIMER_VIRTUAL, {it_interval={0, 10000}, it_value={0, 10000}}, NULL) = 0 --- SIGVTALRM (Virtual timer expired) @ 0 (0) --- --- SIGVTALRM (Virtual timer expired) @ 0 (0) --- --- SIGVTALRM (Virtual timer expired) @ 0 (0) --- --- SIGVTALRM (Virtual timer expired) @ 0 (0) ---

85. But I’m not using threads! begin # require 'net/http' # Net::HTTP.new(host, port).request(...) # require 'net/smtp' # Net::SMTP.new('localhost').send_message(...) require 'timeout' Timeout.timeout(0.1) do 1+2*3/4 while true end rescue Timeout::Error end 500_000_000.times{ |i| i * 2 }

86. But I’m not using threads! begin # require 'net/http' # Net::HTTP.new(host, port).request(...) uses timeout # require 'net/smtp' # Net::SMTP.new('localhost').send_message(...) require 'timeout' Timeout.timeout(0.1) do 1+2*3/4 while true end rescue Timeout::Error end 500_000_000.times{ |i| i * 2 }

87. But I’m not using threads! begin # require 'net/http' # Net::HTTP.new(host, port).request(...) uses timeout # require 'net/smtp' # Net::SMTP.new('localhost').send_message(...) require 'timeout' Timeout.timeout(0.1) do uses threads 1+2*3/4 while true end rescue Timeout::Error end 500_000_000.times{ |i| i * 2 }

88. But I’m not using threads! begin # require 'net/http' # Net::HTTP.new(host, port).request(...) uses timeout # require 'net/smtp' # Net::SMTP.new('localhost').send_message(...) require 'timeout' Timeout.timeout(0.1) do uses threads 1+2*3/4 while true end rescue Timeout::Error end 500_000_000.times{ |i| i * 2 } Thread.new, Timeout.timeout and Net::* all use threads and start the thread timer Once the timer is started, it will interrupt your process every 10ms, even if all threads are killed

89. PATCH: stop the thread timer @@ -10518,6 +10520,15 @@ rb_thread_remove(th) rb_thread_die(th); th->prev->next = th->next; th->next->prev = th->prev; + + /* if this is the last ruby thread, stop timer signals */ + if (th->next == th->prev && th->next == main_thread) { + rb_thread_stop_timer(); + thread_init = 0; + } }

90. PATCH: stop the thread timer @@ -10518,6 +10520,15 @@ rb_thread_remove(th) rb_thread_die(th); th->prev->next = th->next; th->next->prev = th->prev; + + /* if this is the last ruby thread, stop timer signals */ + if (th->next == th->prev && th->next == main_thread) { + rb_thread_stop_timer(); + thread_init = 0; + } } strace -e trace=setitimer ruby threaded.rb setitimer(ITIMER_VIRTUAL, {it_interval={0, 10000}, it_value={0, 10000}}, NULL) = 0 --- SIGVTALRM (Virtual timer expired) @ 0 (0) --- --- SIGVTALRM (Virtual timer expired) @ 0 (0) --- --- SIGVTALRM (Virtual timer expired) @ 0 (0) --- --- SIGVTALRM (Virtual timer expired) @ 0 (0) --- --- SIGVTALRM (Virtual timer expired) @ 0 (0) --- setitimer(ITIMER_VIRTUAL, {it_interval={0, 0}, it_value={0, 0}}, NULL) = 0

92. Why are our debian servers so slow?

93. Why are our debian servers so slow? strace -ttT ruby threaded.rb 18:42:39.566788 rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0 <0.000006> 18:42:39.566836 rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0 <0.000006> 18:42:39.567083 rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0 <0.000006> 18:42:39.567131 rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0 <0.000006> 18:42:39.567415 rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0 <0.000006>

94. Why are our debian servers so slow? strace -c ruby threaded.rb % time seconds usecs/call calls errors syscall ------ ----------- ----------- --------- --------- ---------------- 100.00 0.326334 0 3568567 rt_sigprocmask 0.00 0.000000 0 9 read 0.00 0.000000 0 10 open 0.00 0.000000 0 10 close 0.00 0.000000 0 9 fstat 0.00 0.000000 0 25 mmap ------ ----------- ----------- --------- --------- ---------------- 100.00 0.326334 3568685 0 total strace -ttT ruby threaded.rb 18:42:39.566788 rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0 <0.000006> 18:42:39.566836 rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0 <0.000006> 18:42:39.567083 rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0 <0.000006> 18:42:39.567131 rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0 <0.000006> 18:42:39.567415 rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0 <0.000006>

95. Why are our debian servers so slow? strace -c ruby threaded.rb % time seconds usecs/call calls errors syscall ------ ----------- ----------- --------- --------- ---------------- 100.00 0.326334 0 3568567 rt_sigprocmask 0.00 0.000000 0 9 read 0.00 0.000000 0 10 open 0.00 0.000000 0 10 close 0.00 0.000000 0 9 fstat 0.00 0.000000 0 25 mmap ------ ----------- ----------- --------- --------- ---------------- 100.00 0.326334 3568685 0 total strace -ttT ruby threaded.rb 18:42:39.566788 rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0 <0.000006> 18:42:39.566836 rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0 <0.000006> 18:42:39.567083 rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0 <0.000006> 18:42:39.567131 rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0 <0.000006> 18:42:39.567415 rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0 <0.000006> 3.5 million sigprocmasks.. wtf?

96. What is --enable-pthread anyway? --- config.h.nopthread uses a pthread for +++ config.h @@ -173,6 +173,12 @@ timing instead of #define FILE_READEND _IO_read_end #define HAVE__SC_CLK_TCK 1 setitimer() #define STACK_GROW_DIRECTION -1 +#define _REENTRANT 1 +#define _THREAD_SAFE 1 useful for +#define HAVE_LIBPTHREAD 1 +#define HAVE_NANOSLEEP 1 compatibility with +#define HAVE_GETCONTEXT 1 +#define HAVE_SETCONTEXT 1 external libs that #define DEFAULT_KCODE KCODE_NONE #define USE_ELF 1 use pthreads or #define DLEXT_MAXLEN 3 signals (like ruby- #ifdef _THREAD_SAFE pthread_create(&time_thread, 0, tk) #else thread_timer, 0); rb_thread_start_timer(); #endif

97. What is --enable-pthread anyway? --- config.h.nopthread uses a pthread for +++ config.h @@ -173,6 +173,12 @@ timing instead of #define FILE_READEND _IO_read_end #define HAVE__SC_CLK_TCK 1 setitimer() #define STACK_GROW_DIRECTION -1 +#define _REENTRANT 1 +#define _THREAD_SAFE 1 useful for +#define HAVE_LIBPTHREAD 1 +#define HAVE_NANOSLEEP 1 compatibility with +#define HAVE_GETCONTEXT 1 +#define HAVE_SETCONTEXT 1 external libs that #define DEFAULT_KCODE KCODE_NONE #define USE_ELF 1 use pthreads or #define DLEXT_MAXLEN 3 signals (like ruby- #ifdef _THREAD_SAFE pthread_create(&time_thread, 0, tk) #else thread_timer, 0); rb_thread_start_timer(); #endif but.. it also enables getcontext/ setcontext??

98. What is --enable-pthread anyway? --- config.h.nopthread uses a pthread for +++ config.h @@ -173,6 +173,12 @@ timing instead of #define FILE_READEND _IO_read_end #define HAVE__SC_CLK_TCK 1 setitimer() #define STACK_GROW_DIRECTION -1 +#define _REENTRANT 1 +#define _THREAD_SAFE 1 useful for +#define HAVE_LIBPTHREAD 1 +#define HAVE_NANOSLEEP 1 compatibility with +#define HAVE_GETCONTEXT 1 +#define HAVE_SETCONTEXT 1 external libs that #define DEFAULT_KCODE KCODE_NONE #define USE_ELF 1 use pthreads or #define DLEXT_MAXLEN 3 signals (like ruby- #ifdef _THREAD_SAFE pthread_create(&time_thread, 0, ? tk) #else thread_timer, 0); rb_thread_start_timer(); #endif but.. it also #if defined(HAVE_GETCONTEXT) && enables getcontext/ defined(HAVE_SETCONTEXT) #include <ucontext.h> setcontext?? #define USE_CONTEXT #endif

99. ucontext?

100. ucontext? ruby can use either setjmp/longjmp or setcontext/getcontext in its threading implementation and for exception handling

101. ucontext? ruby can use either setjmp/longjmp or setcontext/getcontext in its threading implementation and for exception handling setjmp/longjmp save and restore the current cpu registers

102. ucontext? ruby can use either setjmp/longjmp or setcontext/getcontext in its threading implementation and for exception handling setjmp/longjmp save and restore the current cpu registers setcontext/getcontext are an advanced version of setjmp/longjmp, but they also call sigprocmask to save/restore the signal mask before each jump

103. PATCH: --disable-ucontext --- a/configure.in +++ b/configure.in @@ -368,6 +368,10 @@ +AC_ARG_ENABLE(ucontext, + [ --disable-ucontext do not use getcontext()/setcontext().], + [disable_ucontext=yes], [disable_ucontext=no]) + AC_ARG_ENABLE(pthread, [ --enable-pthread use pthread library.], [enable_pthread=$enableval], [enable_pthread=no]) @@ -1038,7 +1042,8 @@ -if test x"$ac_cv_header_ucontext_h" = xyes; then +if test x"$ac_cv_header_ucontext_h" = xyes && test x"$disable_ucontext" = xno; then if test x"$rb_with_pthread" = xyes; then AC_CHECK_FUNCS(getcontext setcontext) fi ./configure --enable-pthread --disable-ucontext

104. PATCH: --disable-ucontext --- a/configure.in +++ b/configure.in @@ -368,6 +368,10 @@ +AC_ARG_ENABLE(ucontext, + [ --disable-ucontext do not use getcontext()/setcontext().], + [disable_ucontext=yes], [disable_ucontext=no]) + AC_ARG_ENABLE(pthread, [ --enable-pthread use pthread library.], [enable_pthread=$enableval], [enable_pthread=no]) @@ -1038,7 +1042,8 @@ -if test x"$ac_cv_header_ucontext_h" = xyes; then +if test x"$ac_cv_header_ucontext_h" = xyes && test x"$disable_ucontext" = xno; then if test x"$rb_with_pthread" = xyes; then AC_CHECK_FUNCS(getcontext setcontext) fi ./configure --enable-pthread --disable-ucontext % time seconds usecs/call calls errors syscall ------ ----------- ----------- --------- --------- ---------------- nan 0.000000 0 13 read nan 0.000000 0 21 10 open nan 0.000000 0 11 close ------ ----------- ----------- --------- --------- ---------------- 100.00 0.000000 45 10 total

106. EventMachine + threads = slow?? EventMachine allocates large buffers on the stack to read/write from the network Using threads with EM made ruby extremely slow..

107. EventMachine + threads = slow?? EventMachine allocates large buffers on the stack to read/write from the network Using threads with EM made ruby extremely slow.. ...profile?

108. EventMachine + threads = slow?? EventMachine allocates large buffers on the stack to read/write from the network Using threads with EM made ruby extremely slow.. #include "ruby.h" require 'cext' VALUE bigstack(VALUE self) (1..2).map{ { Thread.new{ char buffer[ 50 * 1024 ]; /* large stack frame */ CExt.bigstack{ if (rb_block_given_p()) rb_yield(Qnil); 100_000.times{ return Qnil; 1*2+3/4 } Thread.pass } void Init_cext() } { } VALUE CExt = rb_define_module("CExt"); }.map{ |t| t.join } rb_define_singleton_method(CExt, "bigstack", bigstack, 0); } ...profile?

113. google-perftools Google’s CPU profiler export LD_PRELOAD=libprofiler.so export DYLD_INSERT_LIBRARIES=libprofiler.dylib CPUPROFILE=/tmp/myprof ./myapp pprof ./myapp /tmp/myprof

114. wget http://google-perftools.googlecode.com/files/google- perftools-1.3.tar.gz tar zxvf google-perftools-1.3.tar.gz cd google-perftools-1.3 ./configure --prefix=/opt make sudo make install # for linux export LD_PRELOAD=/opt/lib/libprofiler.so # for osx export DYLD_INSERT_LIBRARIES=/opt/lib/libprofiler.dylib CPUPROFILE=/tmp/ruby.prof ruby -e' 5_000_000.times{ "hello world" } ' pprof `which ruby` --text /tmp/ruby.prof

115. wget http://google-perftools.googlecode.com/files/google- perftools-1.3.tar.gz download tar zxvf google-perftools-1.3.tar.gz cd google-perftools-1.3 ./configure --prefix=/opt make sudo make install # for linux export LD_PRELOAD=/opt/lib/libprofiler.so # for osx export DYLD_INSERT_LIBRARIES=/opt/lib/libprofiler.dylib CPUPROFILE=/tmp/ruby.prof ruby -e' 5_000_000.times{ "hello world" } ' pprof `which ruby` --text /tmp/ruby.prof

116. wget http://google-perftools.googlecode.com/files/google- perftools-1.3.tar.gz download tar zxvf google-perftools-1.3.tar.gz cd google-perftools-1.3 ./configure --prefix=/opt make compile sudo make install # for linux export LD_PRELOAD=/opt/lib/libprofiler.so # for osx export DYLD_INSERT_LIBRARIES=/opt/lib/libprofiler.dylib CPUPROFILE=/tmp/ruby.prof ruby -e' 5_000_000.times{ "hello world" } ' pprof `which ruby` --text /tmp/ruby.prof

117. wget http://google-perftools.googlecode.com/files/google- perftools-1.3.tar.gz download tar zxvf google-perftools-1.3.tar.gz cd google-perftools-1.3 ./configure --prefix=/opt make compile sudo make install # for linux export LD_PRELOAD=/opt/lib/libprofiler.so setup # for osx export DYLD_INSERT_LIBRARIES=/opt/lib/libprofiler.dylib CPUPROFILE=/tmp/ruby.prof ruby -e' 5_000_000.times{ "hello world" } ' pprof `which ruby` --text /tmp/ruby.prof

118. wget http://google-perftools.googlecode.com/files/google- perftools-1.3.tar.gz download tar zxvf google-perftools-1.3.tar.gz cd google-perftools-1.3 ./configure --prefix=/opt make compile sudo make install # for linux export LD_PRELOAD=/opt/lib/libprofiler.so setup # for osx export DYLD_INSERT_LIBRARIES=/opt/lib/libprofiler.dylib CPUPROFILE=/tmp/ruby.prof ruby -e' profile 5_000_000.times{ "hello world" } ' pprof `which ruby` --text /tmp/ruby.prof

119. wget http://google-perftools.googlecode.com/files/google- perftools-1.3.tar.gz download tar zxvf google-perftools-1.3.tar.gz cd google-perftools-1.3 ./configure --prefix=/opt make compile sudo make install # for linux export LD_PRELOAD=/opt/lib/libprofiler.so setup # for osx export DYLD_INSERT_LIBRARIES=/opt/lib/libprofiler.dylib CPUPROFILE=/tmp/ruby.prof ruby -e' profile 5_000_000.times{ "hello world" } ' pprof `which ruby` --text /tmp/ruby.prof report

120. pprof ruby pprof ruby ruby.prof --text ruby.prof --gif Total: 103 samples 20 19.4% 19.4% 95 92.2% rb_yield_0 11 10.7% 30.1% 103 100.0% rb_eval 8 7.8% 37.9% 12 11.7% gc_sweep 3 2.9% 68.9% 52 50.5% rb_str_new3 3 2.9% 74.8% 3 2.9% obj_free 3 2.9% 77.7% 103 100.0% int_dotimes 3 2.9% 80.6% 12 11.7% gc_mark

121. Profiling EM + threads

122. Profiling EM + threads Total: 3763 samples 2764 73.5% catch_timer 989 26.3% memcpy 3 0.1% st_lookup 2 0.1% rb_thread_schedule 1 0.0% rb_eval 1 0.0% rb_newobj 1 0.0% rb_gc_force_recycle

123. Profiling EM + threads Total: 3763 samples 2764 73.5% catch_timer 989 26.3% memcpy 3 0.1% st_lookup 2 0.1% rb_thread_schedule 1 0.0% rb_eval 1 0.0% rb_newobj 1 0.0% rb_gc_force_recycle rb_thread_save_context

124. Profiling EM + threads Total: 3763 samples 2764 73.5% catch_timer 989 26.3% memcpy 3 0.1% st_lookup 2 0.1% rb_thread_schedule 1 0.0% rb_eval 1 0.0% rb_newobj 1 0.0% rb_gc_force_recycle rb_thread_save_context rb_thread_restore_context

125. Profiling EM + threads Total: 3763 samples 2764 73.5% catch_timer 989 26.3% memcpy 3 0.1% st_lookup 2 0.1% rb_thread_schedule 1 0.0% rb_eval 1 0.0% rb_newobj 1 0.0% rb_gc_force_recycle rb_thread_save_context rb_thread_restore_context memcpy???

126. Profiling EM + threads Total: 3763 samples 2764 73.5% catch_timer 989 26.3% memcpy 3 0.1% st_lookup 2 0.1% rb_thread_schedule 1 0.0% rb_eval 1 0.0% rb_newobj 1 0.0% rb_gc_force_recycle rb_thread_save_context rb_thread_restore_context memcpy??? really? memcpy?

127. ltrace trace library calls ltrace -cp <pid> ltrace -ttTp <pid> -o <file>

128. ltrace -c ruby cext_test.rb

129. ltrace -c ruby cext_test.rb % time seconds usecs/call calls function ------ ----------- ----------- --------- -------------------- 48.65 11.741295 617 19009 memcpy 30.16 7.279634 831 8751 longjmp 9.78 2.359889 135 17357 _setjmp 8.91 2.150565 285 7540 malloc 1.10 0.265946 20 13021 memset 0.81 0.195272 19 10105 __ctype_b_loc 0.35 0.084575 19 4361 strcmp 0.19 0.046163 19 2377 strlen 0.03 0.006272 23 265 realloc ------ ----------- ----------- --------- -------------------- 100.00 24.134999 82999 total

130. ltrace -c ruby cext_test.rb % time seconds usecs/call calls function ------ ----------- ----------- --------- -------------------- 48.65 11.741295 617 19009 memcpy really 30.16 7.279634 831 8751 longjmp 9.78 2.359889 135 17357 _setjmp 8.91 2.150565 285 7540 malloc 1.10 0.265946 20 13021 memset 0.81 0.195272 19 10105 __ctype_b_loc 0.35 0.084575 19 4361 strcmp 0.19 0.046163 19 2377 strlen 0.03 0.006272 23 265 realloc ------ ----------- ----------- --------- -------------------- 100.00 24.134999 82999 total

131. ltrace -c ruby cext_test.rb % time seconds usecs/call calls function ------ ----------- ----------- --------- -------------------- 48.65 11.741295 617 19009 memcpy really 30.16 7.279634 831 8751 longjmp 9.78 2.359889 135 17357 _setjmp 8.91 2.150565 285 7540 malloc 1.10 0.265946 20 13021 memset 0.81 0.195272 19 10105 __ctype_b_loc 0.35 0.084575 19 4361 strcmp 0.19 0.046163 19 2377 strlen 0.03 0.006272 23 265 realloc ------ ----------- ----------- --------- -------------------- 100.00 24.134999 82999 total ltrace -ttT -e memcpy ruby cext_test.rb 01:24:48.769408 --- SIGVTALRM (Virtual timer expired) --- 01:24:48.769616 memcpy(0x1216000, "", 1086328) = 0x1216000 <0.000578> 01:24:48.770555 memcpy(0x6e32670, "240&343v", 1086328) = 0x6e32670 <0.000418> 01:24:49.899414 --- SIGVTALRM (Virtual timer expired) --- 01:24:49.899490 memcpy(0x1320000, "", 1082584) = 0x1320000 <0.000628> 01:24:49.900474 memcpy(0x6e32670, "", 1086328) = 0x6e32670 <0.000479>

132. OK, its calling memcpy() but what is it copying?

133. OK, its calling memcpy() but what is it copying? static void static void rb_thread_save_context(th) rb_thread_restore_context(th) rb_thread_t th; rb_thread_t th; { { VALUE *pos; ruby_frame = th->frame; int len; ruby_scope = th->scope; ruby_setjmp(th->context); /* ... */ len = ruby_stack_length(&pos); MEMCPY(th->stk_pos, th->stk_pos = pos; th->stk_ptr, VALUE, th->stk_len); th->stk_len = len; ruby_longjmp(th->context); MEMCPY(th->stk_ptr, } th->stk_pos, VALUE, th->stk_len); th->frame = ruby_frame; th->scope = ruby_scope; /* ... */ }

134. OK, its calling memcpy() but what is it copying? static void static void rb_thread_save_context(th) rb_thread_restore_context(th) rb_thread_t th; rb_thread_t th; { { VALUE *pos; ruby_frame = th->frame; int len; ruby_scope = th->scope; ruby_setjmp(th->context); /* ... */ len = ruby_stack_length(&pos); MEMCPY(th->stk_pos, th->stk_pos = pos; th->stk_ptr, VALUE, th->stk_len); th->stk_len = len; ruby_longjmp(th->context); MEMCPY(th->stk_ptr, } th->stk_pos, VALUE, th->stk_len); 1. save cpu registers th->frame = ruby_frame; th->scope = ruby_scope; /* ... */ }

136. OK, its calling memcpy() but what is it copying? static void static void rb_thread_save_context(th) rb_thread_restore_context(th) rb_thread_t th; rb_thread_t th; { { VALUE *pos; ruby_frame = th->frame; int len; ruby_scope = th->scope; ruby_setjmp(th->context); /* ... */ len = ruby_stack_length(&pos); MEMCPY(th->stk_pos, th->stk_pos = pos; th->stk_ptr, VALUE, th->stk_len); th->stk_len = len; ruby_longjmp(th->context); MEMCPY(th->stk_ptr, } th->stk_pos, VALUE, th->stk_len); th->frame = ruby_frame; 2. save stack frames th->scope = ruby_scope; /* ... */ }

138. OK, its calling memcpy() but what is it copying? static void static void rb_thread_save_context(th) rb_thread_restore_context(th) rb_thread_t th; rb_thread_t th; { { VALUE *pos; ruby_frame = th->frame; int len; ruby_scope = th->scope; ruby_setjmp(th->context); /* ... */ len = ruby_stack_length(&pos); MEMCPY(th->stk_pos, th->stk_pos = pos; th->stk_ptr, VALUE, th->stk_len); th->stk_len = len; ruby_longjmp(th->context); MEMCPY(th->stk_ptr, } th->stk_pos, VALUE, th->stk_len); th->frame = ruby_frame; th->scope = ruby_scope; 3. save vm globals /* ... */ }

140. OK, its calling memcpy() but what is it copying? static void static void rb_thread_save_context(th) rb_thread_restore_context(th) rb_thread_t th; rb_thread_t th; { { VALUE *pos; ruby_frame = th->frame; int len; ruby_scope = th->scope; ruby_setjmp(th->context); /* ... */ len = ruby_stack_length(&pos); MEMCPY(th->stk_pos, th->stk_pos = pos; th->stk_ptr, VALUE, th->stk_len); th->stk_len = len; ruby_longjmp(th->context); MEMCPY(th->stk_ptr, } th->stk_pos, VALUE, th->stk_len); th->frame = ruby_frame; th->scope = ruby_scope; /* ... */ 4. restore vm globals }

142. OK, its calling memcpy() but what is it copying? static void static void rb_thread_save_context(th) rb_thread_restore_context(th) rb_thread_t th; rb_thread_t th; { { VALUE *pos; ruby_frame = th->frame; int len; ruby_scope = th->scope; ruby_setjmp(th->context); /* ... */ len = ruby_stack_length(&pos); MEMCPY(th->stk_pos, th->stk_pos = pos; th->stk_ptr, VALUE, th->stk_len); th->stk_len = len; ruby_longjmp(th->context); MEMCPY(th->stk_ptr, } th->stk_pos, VALUE, th->stk_len); th->frame = ruby_frame; th->scope = ruby_scope; /* ... */ } 5. restore stack frames

144. OK, its calling memcpy() but what is it copying? static void static void rb_thread_save_context(th) rb_thread_restore_context(th) rb_thread_t th; rb_thread_t th; { { VALUE *pos; ruby_frame = th->frame; int len; ruby_scope = th->scope; ruby_setjmp(th->context); /* ... */ len = ruby_stack_length(&pos); MEMCPY(th->stk_pos, th->stk_pos = pos; th->stk_ptr, VALUE, th->stk_len); th->stk_len = len; ruby_longjmp(th->context); MEMCPY(th->stk_ptr, } th->stk_pos, VALUE, th->stk_len); th->frame = ruby_frame; th->scope = ruby_scope; /* ... */ } 6. restore cpu registers

146. OK, its calling memcpy() but what is it copying? static void static void rb_thread_save_context(th) rb_thread_restore_context(th) rb_thread_t th; rb_thread_t th; { { VALUE *pos; ruby_frame = th->frame; int len; ruby_scope = th->scope; ruby_setjmp(th->context); /* ... */ len = ruby_stack_length(&pos); MEMCPY(th->stk_pos, th->stk_pos = pos; th->stk_ptr, VALUE, th->stk_len); th->stk_len = len; ruby_longjmp(th->context); MEMCPY(th->stk_ptr, } th->stk_pos, VALUE, th->stk_len); th->frame = ruby_frame; th->scope = ruby_scope; /* ... */ } it’s copying the stacks to the heap!

147. Stack vs. Heap

148. Stack vs. Heap Stack:

149. Stack vs. Heap Stack: Storage for local vars

150. Stack vs. Heap Stack: Storage for local vars Only valid while stack frame is on the stack!

151. Stack vs. Heap Stack: Storage for local vars Only valid while stack frame is on the stack! Keeping track of function calls

152. Stack vs. Heap Stack: Heap: Storage for local vars Only valid while stack frame is on the stack! Keeping track of function calls

153. Stack vs. Heap Stack: Heap: Storage for local vars Storage for vars that persist across function Only valid while stack calls. frame is on the stack! Keeping track of function calls

154. Stack vs. Heap Stack: Heap: Storage for local vars Storage for vars that persist across function Only valid while stack calls. frame is on the stack! Managed by malloc Keeping track of function calls

155. Stack vs. Heap func1() void *data; func2(); Stack: Heap: Storage for local vars Storage for vars that persist across function Only valid while stack calls. frame is on the stack! Managed by malloc Keeping track of function calls

156. Stack vs. Heap func1() 4 bytes void *data; func2(); Stack: Heap: Storage for local vars Storage for vars that persist across function Only valid while stack calls. frame is on the stack! Managed by malloc Keeping track of function calls

157. Stack vs. Heap func2() char *string = malloc(10); func3(); func1() 4 bytes void *data; func2(); Stack: Heap: Storage for local vars Storage for vars that persist across function Only valid while stack calls. frame is on the stack! Managed by malloc Keeping track of function calls

158. Stack vs. Heap func2() 4 bytes char *string = malloc(10); func3(); func1() 4 bytes void *data; func2(); Stack: Heap: Storage for local vars Storage for vars that persist across function Only valid while stack calls. frame is on the stack! Managed by malloc Keeping track of function calls

159. Stack vs. Heap func2() 4 bytes char *string = malloc(10); 10 bytes func3(); func1() 4 bytes void *data; func2(); Stack: Heap: Storage for local vars Storage for vars that persist across function Only valid while stack calls. frame is on the stack! Managed by malloc Keeping track of function calls

160. Stack vs. Heap func3() char buffer[8]; func2() 4 bytes char *string = malloc(10); 10 bytes func3(); func1() 4 bytes void *data; func2(); Stack: Heap: Storage for local vars Storage for vars that persist across function Only valid while stack calls. frame is on the stack! Managed by malloc Keeping track of function calls

161. Stack vs. Heap func3() 8 bytes char buffer[8]; func2() 4 bytes char *string = malloc(10); 10 bytes func3(); func1() 4 bytes void *data; func2(); Stack: Heap: Storage for local vars Storage for vars that persist across function Only valid while stack calls. frame is on the stack! Managed by malloc Keeping track of function calls

162. Stack vs. Heap func3() char buffer[8]; func2() 4 bytes char *string = malloc(10); 10 bytes func3(); func1() 4 bytes void *data; func2(); Stack: Heap: Storage for local vars Storage for vars that persist across function Only valid while stack calls. frame is on the stack! Managed by malloc Keeping track of function calls

163. Stack vs. Heap func2() 4 bytes char *string = malloc(10); 10 bytes func3(); func1() 4 bytes void *data; func2(); Stack: Heap: Storage for local vars Storage for vars that persist across function Only valid while stack calls. frame is on the stack! Managed by malloc Keeping track of function calls

164. memcpy()ing the thread stacks

165. memcpy()ing the thread stacks During execution

166. memcpy()ing the thread stacks During execution Saving current thread

167. memcpy()ing the thread stacks During execution Saving current thread Restoring next thread

168. memcpy()ing the thread stacks During execution Saving current thread Restoring next thread so, what’s on these thread stacks?

169. gdb the GNU debugger gdb <program> gdb <program> <pid> Be sure to build with: -ggdb -O0

170. gdb walkthrough

171. gdb walkthrough % gdb ./test-it (gdb) b average Breakpoint 1 at 0x1f8e: file test-it.c, line 3. (gdb) run Starting program: /Users/joe/test-it Reading symbols for shared libraries ++. done Breakpoint 1, average (x=5, y=6) at test-it.c:3 3 int sum = x + y; (gdb) bt #0 average (x=5, y=6) at test-it.c:3 #1 0x00001fec in main () at test-it.c:12 (gdb) s 4 double avg = sum / 2.0; (gdb) s 5 return avg; (gdb) p avg $1 = 5.5 (gdb) p sum $2 = 11

172. gdb walkthrough % gdb ./test-it start gdb (gdb) b average Breakpoint 1 at 0x1f8e: file test-it.c, line 3. (gdb) run Starting program: /Users/joe/test-it Reading symbols for shared libraries ++. done Breakpoint 1, average (x=5, y=6) at test-it.c:3 3 int sum = x + y; (gdb) bt #0 average (x=5, y=6) at test-it.c:3 #1 0x00001fec in main () at test-it.c:12 (gdb) s 4 double avg = sum / 2.0; (gdb) s 5 return avg; (gdb) p avg $1 = 5.5 (gdb) p sum $2 = 11

174. gdb walkthrough % gdb ./test-it (gdb) b average set breakpoint on function named average Breakpoint 1 at 0x1f8e: file test-it.c, line 3. (gdb) run Starting program: /Users/joe/test-it Reading symbols for shared libraries ++. done Breakpoint 1, average (x=5, y=6) at test-it.c:3 3 int sum = x + y; (gdb) bt #0 average (x=5, y=6) at test-it.c:3 #1 0x00001fec in main () at test-it.c:12 (gdb) s 4 double avg = sum / 2.0; (gdb) s 5 return avg; (gdb) p avg $1 = 5.5 (gdb) p sum $2 = 11

176. gdb walkthrough % gdb ./test-it (gdb) b average Breakpoint 1 at 0x1f8e: file test-it.c, line 3. (gdb) run run program Starting program: /Users/joe/test-it Reading symbols for shared libraries ++. done Breakpoint 1, average (x=5, y=6) at test-it.c:3 3 int sum = x + y; (gdb) bt #0 average (x=5, y=6) at test-it.c:3 #1 0x00001fec in main () at test-it.c:12 (gdb) s 4 double avg = sum / 2.0; (gdb) s 5 return avg; (gdb) p avg $1 = 5.5 (gdb) p sum $2 = 11

178. gdb walkthrough % gdb ./test-it (gdb) b average Breakpoint 1 at 0x1f8e: file test-it.c, line 3. (gdb) run Starting program: /Users/joe/test-it Reading symbols for shared libraries ++. done Breakpoint 1, average (x=5, y=6) at test-it.c:3 hit breakpoint! 3 int sum = x + y; (gdb) bt #0 average (x=5, y=6) at test-it.c:3 #1 0x00001fec in main () at test-it.c:12 (gdb) s 4 double avg = sum / 2.0; (gdb) s 5 return avg; (gdb) p avg $1 = 5.5 (gdb) p sum $2 = 11

180. gdb walkthrough % gdb ./test-it (gdb) b average Breakpoint 1 at 0x1f8e: file test-it.c, line 3. (gdb) run Starting program: /Users/joe/test-it Reading symbols for shared libraries ++. done Breakpoint 1, average (x=5, y=6) at test-it.c:3 3 int sum = x + y; (gdb) bt show backtrace #0 average (x=5, y=6) at test-it.c:3 #1 0x00001fec in main () at test-it.c:12 (gdb) s 4 double avg = sum / 2.0; (gdb) s 5 return avg; (gdb) p avg $1 = 5.5 (gdb) p sum $2 = 11

182. gdb walkthrough % gdb ./test-it (gdb) b average Breakpoint 1 at 0x1f8e: file test-it.c, line 3. (gdb) run Starting program: /Users/joe/test-it Reading symbols for shared libraries ++. done Breakpoint 1, average (x=5, y=6) at test-it.c:3 3 int sum = x + y; (gdb) bt #0 average (x=5, y=6) at test-it.c:3 function stack #1 0x00001fec in main () at test-it.c:12 (gdb) s 4 double avg = sum / 2.0; (gdb) s 5 return avg; (gdb) p avg $1 = 5.5 (gdb) p sum $2 = 11

184. gdb walkthrough % gdb ./test-it (gdb) b average Breakpoint 1 at 0x1f8e: file test-it.c, line 3. (gdb) run Starting program: /Users/joe/test-it Reading symbols for shared libraries ++. done Breakpoint 1, average (x=5, y=6) at test-it.c:3 3 int sum = x + y; (gdb) bt #0 average (x=5, y=6) at test-it.c:3 #1 0x00001fec in main () at test-it.c:12 (gdb) s 4 double avg = sum / 2.0; single step (gdb) s 5 return avg; (gdb) p avg $1 = 5.5 (gdb) p sum $2 = 11

186. gdb walkthrough % gdb ./test-it (gdb) b average Breakpoint 1 at 0x1f8e: file test-it.c, line 3. (gdb) run Starting program: /Users/joe/test-it Reading symbols for shared libraries ++. done Breakpoint 1, average (x=5, y=6) at test-it.c:3 3 int sum = x + y; (gdb) bt #0 average (x=5, y=6) at test-it.c:3 #1 0x00001fec in main () at test-it.c:12 (gdb) s 4 double avg = sum / 2.0; (gdb) s 5 return avg; (gdb) p avg $1 = 5.5 print variables (gdb) p sum $2 = 11

188. What’s on the ruby stack? (gdb) where #0 0x0002a55e in rb_call (klass=1386800, recv=5056455, mid=42, argc=1, argv=0xbfffe5c0, scope=0, self=1403220) at eval.c:6125 #1 0x000226ef in rb_eval (self=1403220, n=0x1461e4) at eval.c:3493 #2 0x00026d01 in rb_yield_0 (val=5056455, self=1403220, klass=0, flags=0, avalue=0) at eval.c:5083 #3 0x000270e8 in rb_yield (val=5056455) at eval.c:5168 #4 0x0005c30c in int_dotimes (num=1000000001) at numeric.c:2946 #5 0x00029be3 in call_cfunc (func=0x5c2a0 <int_dotimes>, recv=1000000001, len=0, argc=0, argv=0x0) at eval.c:5759 #6 0x00028fd4 in rb_call0 (klass=1387580, recv=1000000001, id=5785, oid=5785, argc=0, argv=0x0, body=0x152b24, flags=0) at eval.c:5911 #7 0x0002a7a7 in rb_call (klass=1387580, recv=1000000001, mid=5785, argc=0, argv=0x0, scope=0, self=1403220) at eval.c:6158 #8 0x000226ef in rb_eval (self=1403220, n=0x146284) at eval.c:3493 #9 0x000213e3 in rb_eval (self=1403220, n=0x1461a8) at eval.c:3223 #10 0x0001ceea in eval_node (self=1403220, node=0x1461a8) at eval.c:1437 #11 0x0001d60f in ruby_exec_internal () at eval.c:1642 #12 0x0001d660 in ruby_exec () at eval.c:1662 #13 0x0001d68e in ruby_run () at eval.c:1672 #14 0x000023dc in main (argc=2, argv=0xbffff7c4, envp=0xbffff7d0) at main.c:48

197. What’s on the ruby stack? (gdb) where #0 0x0002a55e in rb_call (klass=1386800, recv=5056455, mid=42, argc=1, argv=0xbfffe5c0, scope=0, self=1403220) at eval.c:6125 #1 0x000226ef in rb_eval (self=1403220, n=0x1461e4) at eval.c:3493 #2 0x00026d01 in rb_yield_0 (val=5056455, self=1403220, klass=0, flags=0, avalue=0) at eval.c:5083 #3 0x000270e8 in rb_yield (val=5056455) at eval.c:5168 #4 0x0005c30c in int_dotimes (num=1000000001) at numeric.c:2946 #5 0x00029be3 in call_cfunc (func=0x5c2a0 <int_dotimes>, recv=1000000001, len=0, argc=0, argv=0x0) at eval.c:5759 #6 0x00028fd4 in rb_call0 (klass=1387580, recv=1000000001, id=5785, oid=5785, argc=0, argv=0x0, body=0x152b24, flags=0) at eval.c:5911 #7 0x0002a7a7 in rb_call (klass=1387580, recv=1000000001, mid=5785, argc=0, argv=0x0, scope=0, self=1403220) at eval.c:6158 #8 0x000226ef in rb_eval (self=1403220, n=0x146284) at eval.c:3493 #9 0x000213e3 in rb_eval (self=1403220, n=0x1461a8) at eval.c:3223 #10 0x0001ceea in eval_node (self=1403220, node=0x1461a8) at eval.c:1437 #11 0x0001d60f in ruby_exec_internal () at eval.c:1642 #12 0x0001d660 in ruby_exec () at eval.c:1662 #13 0x0001d68e in ruby_run () at eval.c:1672 #14 0x000023dc in main (argc=2, argv=0xbffff7c4, envp=0xbffff7d0) at main.c:48 rb_eval recursively executes ruby code in 1.8

198. How big is the stack?

199. How big is the stack? #8 rb_eval at eval.c:3493 (gdb) p $ebp - $esp $1 = 968

200. How big is the stack? #8 rb_eval at eval.c:3493 (gdb) p $ebp - $esp base - stack ptr = frame size $1 = 968

201. How big is the stack? #8 rb_eval at eval.c:3493 (gdb) p $ebp - $esp base - stack ptr = frame size $1 = 968 each rb_eval stack frame is almost 1k!

202. How big is the stack? #8 rb_eval at eval.c:3493 (gdb) p $ebp - $esp base - stack ptr = frame size $1 = 968 each rb_eval stack frame is almost 1k! #0 rb_thread_save_context at eval.c:10597 (gdb) p (void*)rb_gc_stack_start - $esp $1 = 10572

203. How big is the stack? #8 rb_eval at eval.c:3493 (gdb) p $ebp - $esp base - stack ptr = frame size $1 = 968 each rb_eval stack frame is almost 1k! #0 rb_thread_save_context at eval.c:10597 (gdb) p (void*)rb_gc_stack_start - $esp $1 = 10572 10.5k stack will be memcpy()’d

204. How big is the stack? #8 rb_eval at eval.c:3493 (gdb) p $ebp - $esp base - stack ptr = frame size $1 = 968 each rb_eval stack frame is almost 1k! #0 rb_thread_save_context at eval.c:10597 (gdb) p (void*)rb_gc_stack_start - $esp $1 = 10572 10.5k stack will be memcpy()’d 50 method calls * 1k ≈ 50k stack

205. Recap: How do Ruby threads work?

206. Recap: How do Ruby threads work? Each thread has it’s own execution context: saved cpu registers (setjmp/longjmp) copy of vm globals (current frame, scope, block) stack (memcpy)

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