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43 lines
1.7 KiB
Groff
43 lines
1.7 KiB
Groff
21 years ago
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.TH io_tryread 3
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.SH NAME
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io_tryread \- read from a descriptor without blocking
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.SH SYNTAX
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.B #include <io.h>
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int \fBio_tryread\fP(int64 fd,char* buf,int64 len);
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.SH DESCRIPTION
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io_tryread tries to read \fIlen\fR bytes of data from descriptor
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\fIfd\fR into buf[0], buf[1], ..., buf[len-1]. (The effects are
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undefined if \fIlen\fR is 0 or smaller.) There are several possible
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results:
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.RS 0
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.IP \[bu] 3
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o_tryread returns an integer between 1 and \fIlen\fR: This number of bytes was
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available for immediate reading; the bytes were read into the beginning
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of \fIbuf\fR. Note that this number can be, and often is, smaller than \fIlen\fR;
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you must not assume that io_tryread always succeeds in reading exactly
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\fIlen\fR bytes.
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.IP \[bu]
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io_tryread returns 0: No bytes were read, because the descriptor is at
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end of file. For example, this descriptor has reached the end of a disk
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file, or is reading an empty pipe that has been closed by all writers.
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.IP \[bu]
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io_tryread returns -1, setting \fIerrno\fR to EAGAIN: No bytes were read,
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because the descriptor is not ready. For example, the descriptor is
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reading an empty pipe that could still be written to.
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.IP \[bu]
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io_tryread returns -3, setting \fIerrno\fR to something other than
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EAGAIN: No bytes were read, because the read attempt encountered a
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persistent error, such as a serious disk failure (EIO), an unreachable
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network (ENETUNREACH), or an invalid descriptor number (EBADF).
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.RE
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io_tryread does not pause waiting for a descriptor that is not ready.
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If you want to pause, use io_waitread or io_wait.
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You can make io_tryread faster and more efficient by making
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the socket non-blocking with io_nonblock().
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.SH "SEE ALSO"
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io_nonblock(3), io_waitread(3), io_tryreadtimeout(3)
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