NAME

       posix_trace_getnext_event,  posix_trace_timedgetnext_event,  posix_trace_trygetnext_event  -  retrieve  a
       trace event (TRACING)

SYNOPSIS

       #include <sys/types.h>
       #include <trace.h>

       int posix_trace_getnext_event(trace_id_t trid,
              struct posix_trace_event_info *restrict event,
              void *restrict data, size_t num_bytes,
              size_t *restrict data_len, int *restrict unavailable);

       int posix_trace_timedgetnext_event(trace_id_t trid,
              struct posix_trace_event_info *restrict event,
              void *restrict data, size_t num_bytes,
              size_t *restrict data_len, int *restrict unavailable,
              const struct timespec *restrict abs_timeout);

       int posix_trace_trygetnext_event(trace_id_t trid,
              struct posix_trace_event_info *restrict event,
              void *restrict data, size_t num_bytes,
              size_t *restrict data_len, int *restrict unavailable);

DESCRIPTION

       The posix_trace_getnext_event() function shall report a recorded trace event either from an active  trace
       stream   without   log    or   a  pre-recorded  trace  stream  identified  by  the  trid  argument.   The
       posix_trace_trygetnext_event() function shall report a recorded trace event from an active  trace  stream
       without log identified by the trid argument.

       The trace event information associated with the recorded trace event shall be copied by the function into
       the  structure  pointed  to  by  the argument event and the data associated with the trace event shall be
       copied into the buffer pointed to by the data argument.

       The posix_trace_getnext_event() function shall block if the trid  argument  identifies  an  active  trace
       stream  and  there is currently no trace event ready to be retrieved. When returning, if a recorded trace
       event was reported, the variable pointed to by the unavailable argument shall be set to zero.  Otherwise,
       the variable pointed to by the unavailable argument shall be set to a value different from zero.

        The posix_trace_timedgetnext_event() function shall attempt to get another trace event  from  an  active
       trace  stream without log, as in the posix_trace_getnext_event() function.  However, if no trace event is
       available from the trace stream, the implied wait shall be terminated when the timeout specified  by  the
       argument abs_timeout expires, and the function shall return the error [ETIMEDOUT].

       The timeout shall expire when the absolute time specified by abs_timeout passes, as measured by the clock
       upon  which  timeouts are based (that is, when the value of that clock equals or exceeds abs_timeout), or
       if the absolute time specified by abs_timeout has already passed at the time of the call.

        If the Timers option is supported, the timeout shall be based on the CLOCK_REALTIME clock; if the Timers
       option is not supported, the timeout shall be based on  the  system  clock  as  returned  by  the  time()
       function.  The  resolution  of the timeout shall be the resolution of the clock on which it is based. The
       timespec data type is defined in the <time.h> header.

       Under no circumstance shall the function fail with a timeout if a trace event  is  immediately  available
       from  the  trace stream. The validity of the abs_timeout argument need not be checked if a trace event is
       immediately available from the trace stream.

       The behavior of this function for a pre-recorded trace stream is unspecified.

       The posix_trace_trygetnext_event() function shall not block.   This function shall return an error if the
       trid argument identifies a pre-recorded trace stream.  If  a  recorded  trace  event  was  reported,  the
       variable  pointed  to  by the unavailable argument shall be set to zero. Otherwise, if no trace event was
       reported, the variable pointed to by the unavailable argument shall be set  to  a  value  different  from
       zero.

       The  argument  num_bytes  shall  be  the size of the buffer pointed to by the data argument. The argument
       data_len reports to the application the length in bytes of the data record just transferred. If num_bytes
       is greater than or equal to the size of the data associated with the trace event pointed to by the  event
       argument,  all  the recorded data shall be transferred. In this case, the truncation-status member of the
       trace event structure shall be either POSIX_TRACE_NOT_TRUNCATED, if the trace  event  data  was  recorded
       without  truncation while tracing, or POSIX_TRACE_TRUNCATED_RECORD, if the trace event data was truncated
       when it was recorded. If the num_bytes argument is less than the length of recorded trace event data, the
       data transferred shall be truncated to a length of num_bytes, the value stored in the variable pointed to
       by data_len shall be equal to num_bytes, and the truncation-status member of the event structure argument
       shall  be  set  to  POSIX_TRACE_TRUNCATED_READ  (see  the  posix_trace_event_info  structure  defined  in
       <trace.h>).

       The  report  of  a  trace  event shall be sequential starting from the oldest recorded trace event. Trace
       events shall be reported in the order in which they were generated, up to an implementation-defined  time
       resolution  that  causes  the  ordering of trace events occurring very close to each other to be unknown.
       Once reported, a trace event cannot be reported again from an active trace stream. Once a trace event  is
       reported  from  an  active trace stream without log, the trace stream shall make the resources associated
       with that trace event available to record future generated trace events.

RETURN VALUE

       Upon successful completion, these functions shall return a value of zero. Otherwise,  they  shall  return
       the corresponding error number.

       If successful, these functions store:

        * The recorded trace event in the object pointed to by event

        * The trace event information associated with the recorded trace event in the object pointed to by data

        * The length of this trace event information in the object pointed to by data_len

        * The value of zero in the object pointed to by unavailable

ERRORS

       These functions shall fail if:

       EINVAL The trace stream identifier argument trid is invalid.

       The posix_trace_getnext_event() and posix_trace_timedgetnext_event() functions shall fail if:

       EINTR  The operation was interrupted by a signal, and so the call had no effect.

       The posix_trace_trygetnext_event() function shall fail if:

       EINVAL The trace stream identifier argument trid does not correspond to an active trace stream.

       The posix_trace_timedgetnext_event() function shall fail if:

       EINVAL There  is  no trace event immediately available from the trace stream, and the timeout argument is
              invalid.

       ETIMEDOUT
              No trace event was available from the trace stream before the specified timeout timeout expired.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       None.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       posix_trace_create()  ,  posix_trace_open()  ,  the  Base  Definitions  volume  of  IEEE Std 1003.1-2001,
       <sys/types.h>, <trace.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
       Standard  for  Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers,
       Inc and The Open Group. In the event of any discrepancy between this version and the  original  IEEE  and
       The  Open  Group  Standard,  the  original  IEEE and The Open Group Standard is the referee document. The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group                                   2003                          POSIX_TRACE_GETNEXT_EVENT(P)