05-24-2016
Quote:
Originally Posted by
aderamos12
Thanks for the reply.
Will it not be an endless loop if I will not put a counter to it? Or an end of file flag?
No! After the last line in your file is read, the next read will report that it found end-of-file. No special flags are needed. When you read from a regular file, and no more data is available, the read() system call will return 0 (no data available). When you read from a pipe and no more data is available at that moment, the read() system call will hang until more data is available (in which case it will return the data available at that time or the number of bytes requested, whichever is smaller) or all file descriptors open for writing to that pipe have been closed (in which case it will return 0).
The operating system knows how big a file is and won't return more data to the user than what exists in the file.
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PIPE(3) Library Functions Manual PIPE(3)
NAME
pipe - two-way interprocess communication
SYNOPSIS
bind #| dir
dir/data
dir/ctl
dir/data1
dir/ctl1
DESCRIPTION
An attach(5) of this device allocates two new streams joined at the device end. X/data and x/ctl are the data and control channels of one
stream and x/data1 and x/ctl1 are the data and control channels of the other stream.
Data written to one channel becomes available for reading at the other. Write boundaries are preserved: each read terminates when the read
buffer is full or after reading the last byte of a write, whichever comes first.
Written data is buffered in kernel stream blocks. The writer will block once the stream is full, typically after 32768 bytes or 16 writes.
The writer will resume once the stream is less than half full.
If there are multiple writers, each write is guaranteed to be available in a contiguous piece at the other end of the pipe. If there are
multiple readers, each read will return data from only one write.
The pipe(2) system call performs an attach of this device and returns file descriptors to the new pipe's data and data1 files. The files
are open with mode ORDWR.
SEE ALSO
pipe(2)
SOURCE
/sys/src/9/port/devpipe.c
PIPE(3)