- strace
  strace -o strace.txt -ttT -s 1024 -p `pgrep nutcracker`

- libyaml (yaml-0.1.4)

  - yaml tokens:

  0  YAML_NO_TOKEN,
  1  YAML_STREAM_START_TOKEN,
  2  YAML_STREAM_END_TOKEN,
  3  YAML_VERSION_DIRECTIVE_TOKEN,
  4  YAML_TAG_DIRECTIVE_TOKEN,
  5  YAML_DOCUMENT_START_TOKEN,
  6  YAML_DOCUMENT_END_TOKEN,
  7  YAML_BLOCK_SEQUENCE_START_TOKEN,
  8  YAML_BLOCK_MAPPING_START_TOKEN,
  9  YAML_BLOCK_END_TOKEN,
  10 YAML_FLOW_SEQUENCE_START_TOKEN,
  11 YAML_FLOW_SEQUENCE_END_TOKEN,
  12 YAML_FLOW_MAPPING_START_TOKEN,
  13 YAML_FLOW_MAPPING_END_TOKEN,
  14 YAML_BLOCK_ENTRY_TOKEN,
  15 YAML_FLOW_ENTRY_TOKEN,
  16 YAML_KEY_TOKEN,
  17 YAML_VALUE_TOKEN,
  18 YAML_ALIAS_TOKEN,
  19 YAML_ANCHOR_TOKEN,
  20 YAML_TAG_TOKEN,
  21 YAML_SCALAR_TOKEN

  - yaml events

  0  YAML_NO_EVENT,
  1  YAML_STREAM_START_EVENT,
  2  YAML_STREAM_END_EVENT,
  3  YAML_DOCUMENT_START_EVENT,
  4  YAML_DOCUMENT_END_EVENT,
  5  YAML_ALIAS_EVENT,
  6  YAML_SCALAR_EVENT,
  7  YAML_SEQUENCE_START_EVENT,
  8  YAML_SEQUENCE_END_EVENT,
  9  YAML_MAPPING_START_EVENT,
  10 YAML_MAPPING_END_EVENT

- sys/queue.h

  queue.h is a generic linked list library adapted from BSD. It has three
  macro knobs that are useful for debugging:

  - QUEUE_MACRO_SCRUB nullifies links (next and prev pointers) of deleted
    elements and catches cases where we are attempting to do operations
    on an element that has already been unlinked.
  - QUEUE_MACRO_TRACE keeps track of __FILE__ and __LINE__ of last two
    updates to the list data structure.
  - QUEUE_MACRO_ASSERT verifies the sanity of list data structure on every
    operation.

- valgrind
  valgrind --tool=memcheck --leak-check=yes <program>

- Core dump
  ulimit -c unlimited

- Generate ENOMEM to test "Out of Memory"
  ulimit -m <size>    # limit maximum memory size
  ulimit -v <size>    # limit virtual memory

- get nutcracker stats
  printf "" | socat  - TCP:localhost:22222 | tee stats.txt
  printf "" | nc localhost 22222 | python -mjson.tool

- Signalling and Logging
  SIGTTIN - To up the log level
  SIGTTOU - To down the log level
  SIGHUP  - To reopen log file

- Error codes:
  http://www.cs.utah.edu/dept/old/texinfo/glibc-manual-0.02/library_2.html
  /usr/include/asm-generic/errno-base.h
  /usr/include/asm-generic/errno.h

- epoll (linux)

  union epoll_data {
      void *ptr;
      int fd;
      uint32_t u32;
      uint64_t u64;
  };

  struct epoll_event {
      uint32_t          events;  /* epoll events */
      struct epoll_data data;    /* user data variable */
  };

  /* events */
  EPOLLIN       = 0x001,
  EPOLLPRI      = 0x002,
  EPOLLOUT      = 0x004,
  EPOLLERR      = 0x008,
  EPOLLHUP      = 0x010,
  EPOLLRDNORM   = 0x040,
  EPOLLRDBAND   = 0x080,
  EPOLLWRNORM   = 0x100,
  EPOLLWRBAND   = 0x200,
  EPOLLMSG      = 0x400,
  EPOLLRDHUP    = 0x2000,
  EPOLLONESHOT  = (1 << 30),
  EPOLLET       = (1 << 31)

  /* opcodes */
  EPOLL_CTL_ADD = 1 /* add a file decriptor to the interface */
  EPOLL_CTL_DEL = 2 /* remove a file decriptor from the interface */
  EPOLL_CTL_MOD = 3 /* change file decriptor epoll_event structure */

- kqueue (bsd)

  struct kevent {
      uintptr_t   ident;    /* identifier for this event */
      int16_t     filter;   /* filter for event */
      uint16_t    flags;    /* general flags */
      uint32_t    fflags;   /* filter-specific flags */
      intptr_t    data;     /* filter-specific data */
      void        *udata;   /* opaque user data identifier */
  };

  /* flags / events */
  EV_ADD        = 0x0001    /* action - add event to kq (implies enable) */
  EV_DELETE     = 0x0002    /* action - delete event from kq */
  EV_ENABLE     = 0x0004    /* action - enable event */
  EV_DISABLE    = 0x0008    /* action - disable event (not reported) */
  EV_RECEIPT    = 0x0040    /* action - force EV_ERROR on success, data == 0 */

  EV_ONESHOT    = 0x0010    /* flags - only report one occurrence */
  EV_CLEAR      = 0x0020    /* flags - clear event state after reporting */
  EV_DISPATCH   = 0x0080    /* flags - disable event after reporting */
  EV_SYSFLAGS   = 0xF000    /* flags - reserved by system */
  EV_FLAG0      = 0x1000    /* flags - filter-specific flag */
  EV_FLAG1      = 0x2000    /* flags - filter-specific flag */

  EV_EOF        = 0x8000    /* returned values - EOF detected */
  EV_ERROR      = 0x4000    /* returned values - error, data contains errno */

  /* filters */
  EVFILT_READ       (-1)    /* readable */
  EVFILT_WRITE      (-2)    /* writable */
  EVFILT_AIO        (-3)    /* attached to aio requests */
  EVFILT_VNODE      (-4)    /* attached to vnodes */
  EVFILT_PROC       (-5)    /* attached to struct proc */
  EVFILT_SIGNAL     (-6)    /* attached to struct proc */
  EVFILT_TIMER      (-7)    /* timers */
  EVFILT_MACHPORT   (-8)    /* mach portsets */
  EVFILT_FS         (-9)    /* filesystem events */
  EVFILT_USER       (-10)   /* user events */
  EVFILT_VM         (-12)   /* virtual memory events */

  EV_CLEAR behaves like EPOLLET because it resets the event after it is
  returned; without this flag, the event would be repeatedly returned.

- poll (unix)

  POLLIN       0x001    /* there is data to read */
  POLLPRI      0x002    /* there is urgent data to read */
  POLLOUT      0x004    /* writing now will not block */

  POLLRDNORM   0x040    /* normal data may be read */
  POLLRDBAND   0x080    /* priority data may be read */
  POLLWRNORM   0x100    /* writing now will not block */
  POLLWRBAND   0x200    /* priority data may be written */

  POLLMSG      0x400
  POLLREMOVE  0x1000
  POLLRDHUP   0x2000

  POLLERR	   0x008    /* error condition */
  POLLHUP      0x010    /* hung up */
  POLLNVAL     0x020    /* invalid polling request */

- event ports (solaris)

  typedef struct port_event {
      int         portev_events;  /* event data is source specific */
      ushort_t    portev_source;  /* event source */
      ushort_t    portev_pad;     /* port internal use */
      uintptr_t   portev_object;  /* source specific object */
      void        *portev_user;   /* user cookie */
  } port_event_t;

  /* port sources */
  PORT_SOURCE_AIO     1
  PORT_SOURCE_TIMER   2
  PORT_SOURCE_USER    3
  PORT_SOURCE_FD      4
  PORT_SOURCE_ALERT   5
  PORT_SOURCE_MQ      6
  PORT_SOURCE_FILE    7