
  [;1m-spec erlang:system_monitor(MonitorPid, Options) -> MonSettings[0m
  [;1m                               when[0m
  [;1m                                   MonitorPid :: pid(),[0m
  [;1m                                   Options :: [system_monitor_option()],[0m
  [;1m                                   MonSettings ::[0m
  [;1m                                       undefined |[0m
  [;1m                                       {OldMonitorPid, OldOptions},[0m
  [;1m                                   OldMonitorPid :: pid(),[0m
  [;1m                                   OldOptions ::[0m
  [;1m                                       [system_monitor_option()].[0m

  Types:
    -type system_monitor_option() ::
          busy_port | busy_dist_port |
          {long_gc, non_neg_integer()} |
          {long_schedule, non_neg_integer()} |
          {large_heap, non_neg_integer()}.

  Sets the system performance monitoring options. [;;4mMonitorPid[0m is a
  local process identifier (pid) receiving system monitor messages.
  The second argument is a list of monitoring options:

  [;;4m[;;4m{long_gc, Time}[0m[0m:
    If a garbage collection in the system takes at least [;;4mTime[0m
    wall clock milliseconds, a message [;;4m{monitor, GcPid, long_gc,[0m
    [;;4mInfo}[0m is sent to [;;4mMonitorPid[0m. [;;4mGcPid[0m is the pid that was
    garbage collected. [;;4mInfo[0m is a list of two-element tuples
    describing the result of the garbage collection.

    One of the tuples is [;;4m{timeout, GcTime}[0m, where [;;4mGcTime[0m is
    the time for the garbage collection in milliseconds. The other
    tuples are tagged with [;;4mheap_size[0m, [;;4mheap_block_size[0m, [;;4m[0m
    [;;4mstack_size[0m, [;;4mmbuf_size[0m, [;;4mold_heap_size[0m, and [;;4m[0m
    [;;4mold_heap_block_size[0m. These tuples are explained in the
    description of trace message [;;4mgc_minor_start[0m (see [;;4m[0m
    [;;4merlang:trace/3[0m). New tuples can be added, and the order of
    the tuples in the [;;4mInfo[0m list can be changed at any time
    without prior notice.

  [;;4m[;;4m{long_schedule, Time}[0m[0m:
    If a process or port in the system runs uninterrupted for at
    least [;;4mTime[0m wall clock milliseconds, a message [;;4m{monitor,[0m
    [;;4mPidOrPort, long_schedule, Info}[0m is sent to [;;4mMonitorPid[0m. [;;4m[0m
    [;;4mPidOrPort[0m is the process or port that was running. [;;4mInfo[0m is
    a list of two-element tuples describing the event.

    If a [;;4mpid()[0m, the tuples [;;4m{timeout, Millis}[0m, [;;4m{in, Location}[0m,
    and [;;4m{out, Location}[0m are present, where [;;4mLocation[0m is either
    an MFA ([;;4m{Module, Function, Arity}[0m) describing the function
    where the process was scheduled in/out, or the atom [;;4mundefined[0m.

    If a [;;4mport()[0m, the tuples [;;4m{timeout, Millis}[0m and [;;4m[0m
    [;;4m{port_op,Op}[0m are present. [;;4mOp[0m is one of [;;4mproc_sig[0m, [;;4mtimeout[0m, [;;4m[0m
    [;;4minput[0m, [;;4moutput[0m, [;;4mevent[0m, or [;;4mdist_cmd[0m, depending on which
    driver callback was executing.

    [;;4mproc_sig[0m is an internal operation and is never to appear,
    while the others represent the corresponding driver callbacks [;;4m[0m
    [;;4mtimeout[0m, [;;4mready_input[0m, [;;4mready_output[0m, [;;4mevent[0m, and [;;4moutputv[0m
    (when the port is used by distribution). Value [;;4mMillis[0m in
    tuple [;;4mtimeout[0m informs about the uninterrupted execution time
    of the process or port, which always is equal to or higher
    than the [;;4mTime[0m value supplied when starting the trace. New
    tuples can be added to the [;;4mInfo[0m list in a future release.
    The order of the tuples in the list can be changed at any time
    without prior notice.

    This can be used to detect problems with NIFs or drivers that
    take too long to execute. 1 ms is considered a good maximum
    time for a driver callback or a NIF. However, a time-sharing
    system is usually to consider everything < 100 ms as
    "possible" and fairly "normal". However, longer schedule times
    can indicate swapping or a misbehaving NIF/driver. Misbehaving
    NIFs and drivers can cause bad resource utilization and bad
    overall system performance.

  [;;4m[;;4m{large_heap, Size}[0m[0m:
    If a garbage collection in the system results in the allocated
    size of a heap being at least [;;4mSize[0m words, a message [;;4m[0m
    [;;4m{monitor, GcPid, large_heap, Info}[0m is sent to [;;4mMonitorPid[0m. [;;4m[0m
    [;;4mGcPid[0m and [;;4mInfo[0m are the same as for [;;4mlong_gc[0m earlier,
    except that the tuple tagged with [;;4mtimeout[0m is not present.

    The monitor message is sent if the sum of the sizes of all
    memory blocks allocated for all heap generations after a
    garbage collection is equal to or higher than [;;4mSize[0m.

    When a process is killed by [;;4mmax_heap_size[0m, it is killed
    before the garbage collection is complete and thus no large
    heap message is sent.

  [;;4m[;;4mbusy_port[0m[0m:
    If a process in the system gets suspended because it sends to
    a busy port, a message [;;4m{monitor, SusPid, busy_port, Port}[0m is
    sent to [;;4mMonitorPid[0m. [;;4mSusPid[0m is the pid that got suspended
    when sending to [;;4mPort[0m.

  [;;4m[;;4mbusy_dist_port[0m[0m:
    If a process in the system gets suspended because it sends to
    a process on a remote node whose inter-node communication was
    handled by a busy port, a message [;;4m{monitor, SusPid,[0m
    [;;4mbusy_dist_port, Port}[0m is sent to [;;4mMonitorPid[0m. [;;4mSusPid[0m is
    the pid that got suspended when sending through the inter-node
    communication port [;;4mPort[0m.

  Returns the previous system monitor settings just like [;;4m[0m
  [;;4merlang:system_monitor/0[0m.

  The arguments to [;;4msystem_monitor/2[0m specifies how all system
  monitoring on the node should be done, not how it should be
  changed. This means only one process at a time ([;;4mMonitorPid[0m) can
  be the receiver of system monitor messages. Also, the way to clear
  a specific monitor option is to not include it in the list [;;4m[0m
  [;;4mOptions[0m. All system monitoring will, however, be cleared if the
  process identified by [;;4mMonitorPid[0m terminates.

  There are no special option values (like zero) to clear an option.
  Some of the options have a unspecified minimum value. Lower values
  will be adjusted to the minimum value. For example, it is
  currently not possible to monitor all garbage collections with [;;4m[0m
  [;;4m{long_gc, 0}[0m.

  Note:
    If a monitoring process gets so large that it itself starts to
    cause system monitor messages when garbage collecting, the
    messages enlarge the process message queue and probably make
    the problem worse.

    Keep the monitoring process neat and do not set the system
    monitor limits too tight.

  Failures:

  [;;4m[;;4mbadarg[0m[0m:
    If [;;4mMonitorPid[0m does not exist.

  [;;4m[;;4mbadarg[0m[0m:
    If [;;4mMonitorPid[0m is not a local process.
