testb.9

7号信令功能代码,为开源代码

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.TH TESTB 9 "2004/01/12 23:33:12" "LiS-2_16_18-8" "Linux STREAMS DDI/DKI"
.SH NAME
.B testb, lis_testb
\- test is a \fISTREAMS\fR message can be allocated
.SH SYNOPSIS
.PP
.B #include <sys/stream.h>
.HP 8
.BI "int " retval " = testb(int " size ", unsigned int " priority );
.SH DESCRIPTION
.PP
.BR testb ()
tests whether an allocation made with
.BR allocb (9)
of the size specified by
.I size
and priority specified by
.IR priority ,
will succeed or fail.
To test whether a subsequent allocation with
.BR esballoc (9)
will succeed or fail, set
.I size
to zero (0).
.PP
.I priority
can be one of the following values:
.TP 12
.B BPRI_LO
The caller requests a low priority message buffer.
.TP 12
.B BPRI_MED
The caller requests a medium priority message buffer.
.TP 12
.B BPRI_HI
The caller requests a high priority message buffer.
.SH "RETURN VALUES"
.PP
.BR testb ()
returns true (1) if the allocate would succeed, and returns false (0) if the
allocation would fail.
.SH ERRORS
.PP
.BR testb ()
always succeeds.
.SH CAVEATS
.PP
As with other post SVR 3 STREAMS
.[
svr3
.]
implementations,
.B LiS
.[
LiS
.]
ignores the
.I priority
argument to
.BR testb () .
The message block
.I priority
was an SVR 3
.[
svr3
.]
concept which was found not to be useful, primarily due to
priority inversion.  For a history of the
.I priority
mechanism and a discussion as to why the mechanism was abandonned in SVR 4.2,
.[
svr42
.]
see \*(lqThe Magic Garden Explained\*(rq section 7.7.2.
.[
magic
.]
.PP
.BR testb ()
can only test whether the allocation would succeed at a given moment in time.
It cannot indicate what would happen immediately following return from
.BR testb ().
Therefore, the return from
.BR allocb "(9) and " esballoc (9)
must always be tested for
.BR NULL .
.SH "SEE ALSO"
.PP
.BR allocb (9),
.BR esballoc (9).
.SH VERSIONS
.PP
This manpage was written for
.B LiS\c
.
.[
LiS
.]
.PP
.BR testb ()
first appeared in SVR 3.
.[
svr3
.]
.\"
.\"
.XX
.[
magic
.]
.[
svr42
.]
.[
svr4
.]
.\"
.\"
.[
$LIST$
.]
.TA