Tue Jul 30 09:21:14 2002
Standard preamble:
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\\$1
.. ..
.... Set up some character translations and predefined strings. \*(-- will
give an unbreakable dash, \*(PI will give pi, \*(L" will give a left
double quote, and \*(R" will give a right double quote. | will give a
real vertical bar. \*(C+ will give a nicer C++. Capital omega is used
to do unbreakable dashes and therefore won't be available. \*(C` and
\*(C' expand to `' in nroff, nothing in troff, for use with C<>
.tr \(*W-|\(bv\*(Tr . ds -- \(*W- . ds PI pi . if (\n(.H=4u)&(1m=24u) .ds -- \(*W\h'-12u'\(*W\h'-12u'-\" diablo 10 pitch . if (\n(.H=4u)&(1m=20u) .ds -- \(*W\h'-12u'\(*W\h'-8u'-\" diablo 12 pitch . ds L" "" . ds R" "" . ds C` "" . ds C' "" 'br\} . ds -- \|\(em\| . ds PI \(*p . ds L" `` . ds R" '' 'br\}
If the F register is turned on, we'll generate index entries on stderr
for titles (.TH), headers (.SH), subsections (.Sh), items (.Ip), and
index entries marked with X<> in POD. Of course, you'll have to process
the output yourself in some meaningful fashion.
. de IX . tm Index:\\$1\t\\n%\t"\\$2" .. . nr % 0 . rr F .\}
For nroff, turn off justification. Always turn off hyphenation; it
makes way too many mistakes in technical documents.
Accent mark definitions (@(#)ms.acc 1.5 88/02/08 SMI; from UCB 4.2).
Fear. Run. Save yourself. No user-serviceable parts.
.bd B 3 . \" fudge factors for nroff and troff . ds #H 0 . ds #V .8m . ds #F .3m . ds #[ \f1 . ds #] .\} . ds #H ((1u-(\\\\n(.fu%2u))*.13m) . ds #V .6m . ds #F 0 . ds #[ \& . ds #] \& .\} . \" simple accents for nroff and troff . ds ' \& . ds ` \& . ds ^ \& . ds , \& . ds ~ ~ . ds / .\} . ds ' \\k:\h'-(\\n(.wu*8/10-\*(#H)'\'\h"|\\n:u" . ds ` \\k:\h'-(\\n(.wu*8/10-\*(#H)'\`\h'|\\n:u' . ds ^ \\k:\h'-(\\n(.wu*10/11-\*(#H)'^\h'|\\n:u' . ds , \\k:\h'-(\\n(.wu*8/10)',\h'|\\n:u' . ds ~ \\k:\h'-(\\n(.wu-\*(#H-.1m)'~\h'|\\n:u' . ds / \\k:\h'-(\\n(.wu*8/10-\*(#H)'\z\(sl\h'|\\n:u' .\} . \" troff and (daisy-wheel) nroff accents . \" corrections for vroff . \" for low resolution devices (crt and lpr) \{\ . ds : e . ds 8 ss . ds o a . ds d- d\h'-1'\(ga . ds D- D\h'-1'\(hy . ds th \o'bp' . ds Th \o'LP' . ds ae ae . ds Ae AE .\} ======================================================================
Title "BIO_should_retry 3"
\fIBIO_should_retry() is true if the call that produced this condition should then be retried at a later time.
If BIO_should_retry() is false then the cause is an error condition.
\fIBIO_should_read() is true if the cause of the condition is that a \s-1BIO\s0 needs to read data.
\fIBIO_should_write() is true if the cause of the condition is that a \s-1BIO\s0 needs to read data.
\fIBIO_should_io_special() is true if some \*(L"special\*(R" condition, that is a reason other than reading or writing is the cause of the condition.
\fIBIO_get_retry_reason() returns a mask of the cause of a retry condition consisting of the values \s-1BIO_FLAGS_READ\s0, \s-1BIO_FLAGS_WRITE\s0, \fB\s-1BIO_FLAGS_IO_SPECIAL\s0 though current \s-1BIO\s0 types will only set one of these.
\fIBIO_get_retry_BIO() determines the precise reason for the special condition, it returns the \s-1BIO\s0 that caused this condition and if \fBreason is not \s-1NULL\s0 it contains the reason code. The meaning of the reason code and the action that should be taken depends on the type of \s-1BIO\s0 that resulted in this condition.
\fIBIO_get_retry_reason() returns the reason for a special condition if passed the relevant \s-1BIO\s0, for example as returned by BIO_get_retry_BIO().
If the underlying I/O structure is in a blocking mode almost all current \s-1BIO\s0 types will not request a retry, because the underlying I/O calls will not. If the application knows that the \s-1BIO\s0 type will never signal a retry then it need not call BIO_should_retry() after a failed \s-1BIO\s0 I/O call. This is typically done with file BIOs.
\s-1SSL\s0 BIOs are the only current exception to this rule: they can request a retry even if the underlying I/O structure is blocking, if a handshake occurs during a call to BIO_read(). An application can retry the failed call immediately or avoid this situation by setting \s-1SSL_MODE_AUTO_RETRY\s0 on the underlying \s-1SSL\s0 structure.
While an application may retry a failed non blocking call immediately this is likely to be very inefficient because the call will fail repeatedly until data can be processed or is available. An application will normally wait until the necessary condition is satisfied. How this is done depends on the underlying I/O structure.
For example if the cause is ultimately a socket and BIO_should_read() is true then a call to select() may be made to wait until data is available and then retry the \s-1BIO\s0 operation. By combining the retry conditions of several non blocking BIOs in a single select() call it is possible to service several BIOs in a single thread, though the performance may be poor if \s-1SSL\s0 BIOs are present because long delays can occur during the initial handshake process.
It is possible for a \s-1BIO\s0 to block indefinitely if the underlying I/O structure cannot process or return any data. This depends on the behaviour of the platforms I/O functions. This is often not desirable: one solution is to use non blocking I/O and use a timeout on the select() (or equivalent) call.