The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.

#### NAME

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

#### SYNOPSIS

> ``[TRC] #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`);
> ``
> ``[TRC TMO] 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`);
> ``
> ``[TRC] 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 [TRL] 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.

> [TMO] 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.

> [TMO TMR] 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.

> [TMO] 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. [TRL] 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.

> [TMO] 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>

#### CHANGE HISTORY

> First released in Issue 6. Derived from IEEE Std 1003.1q-2000.

> IEEE PASC Interpretation 1003.1 #123 is applied.

End of informative text.

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