Hi Fooler, Zak, Brian, etc: Thank you so much for your input on this. Much appreciated.
Regards, Ludwig ----- Original Message ----- > From: fooler mail <[email protected]> > To: Ludwig Isaac Lim <[email protected]>; Philippine Linux Users' Group > (PLUG) Technical Discussion List <[email protected]> > Cc: > Sent: Monday, September 26, 2011 11:50 PM > Subject: Re: [plug] Perl and buffering > > On Mon, Sep 26, 2011 at 3:57 PM, Ludwig Isaac Lim <[email protected]> > wrote: >> Hi: >> Thanks for the quick response. Since according to definition of line >> buffering (see below), a buffer is flushed is after newlines, so writing >> statements such as : >> print "<p> This is a paragraph</p>\n" >> >> in a CGI program will automatically flush the buffer right? Or it >> doesn't? I wondering if perl will figure out that since STDOUT is not >> connected to a terminal, it will still buffer it even though the print >> contains a newline. > > hi ludwig, > > you need to understand the buffering system of standard i/o library.. > > there are 3 kinds of buffering.. > > 1. fully buffered > 2. line bufffered > 3. unbuffered > > the goal of buffering is to minimize number of read and write > expensive system calls... > > in fully buffered.. actual i/o takes place when allocated buffer is > filled... for example files in a disk are normally fully buffered.. > when you read data from a file.. data from kernel land to user land > delivered when bufer is filled... when you write a data to a file.. > disk write takes place (flush) when buffer is filled.. > > in line buffered.. actual i/o takes place either allocated buffer is > filled or new line character is encountered on input or output stream > whichever comes first... for example interactive device such as > terminal device is normally line buffered.. > > in unbuffered.. i/o takes place immediately... for example.. standard > error is normally unbuffered... error messages are displayed as soon > and quickly as possible... > > ANSI C requiers the following buffering characteristics... > > 1. standard input and standard output are fully buffered as long as > they do not refer to an interactive device.. > 2. standard error is never fully buffered... > > in your CGI program... if you run that in interactive mode... print > command is line buffered because standard output is connected to a > terminal device.... if you run that as a server and output connected > to a socket... it is a fully buffered because socket is fully > buffered.. > > if you dont like these defaults of any given standard i/o stream or > you want to change its characteristic from fully buffered to line > buffered for example.. you can use "setvbuf" function call and > specify the mode you want... > > _IOFBF = fully buffered > _IOLBF = line buffered > _IONBF = unbuffered > > $| is equivalent to line buffered as it flushes after write or print command.. > > fooler. > _________________________________________________ Philippine Linux Users' Group (PLUG) Mailing List http://lists.linux.org.ph/mailman/listinfo/plug Searchable Archives: http://archives.free.net.ph
