PHP 5.5.15 is released

flush

(PHP 4, PHP 5)

flushFlush the output buffer

Description

void flush ( void )

Flushes the write buffers of PHP and whatever backend PHP is using (CGI, a web server, etc). This attempts to push current output all the way to the browser with a few caveats.

flush() may not be able to override the buffering scheme of your web server and it has no effect on any client-side buffering in the browser. It also doesn't affect PHP's userspace output buffering mechanism. This means you will have to call both ob_flush() and flush() to flush the ob output buffers if you are using those.

Several servers, especially on Win32, will still buffer the output from your script until it terminates before transmitting the results to the browser.

Server modules for Apache like mod_gzip may do buffering of their own that will cause flush() to not result in data being sent immediately to the client.

Even the browser may buffer its input before displaying it. Netscape, for example, buffers text until it receives an end-of-line or the beginning of a tag, and it won't render tables until the </table> tag of the outermost table is seen.

Some versions of Microsoft Internet Explorer will only start to display the page after they have received 256 bytes of output, so you may need to send extra whitespace before flushing to get those browsers to display the page.

Return Values

No value is returned.

add a note add a note

User Contributed Notes 31 notes

up
15
js at jeansebastien dot com
9 years ago
This will show each line at a time with a pause of 2 seconds.
(Tested under IEx and Firefox)

<?php

if (ob_get_level() == 0) ob_start();

for (
$i = 0; $i<10; $i++){

        echo
"<br> Line to show.";
        echo
str_pad('',4096)."\n";   

       
ob_flush();
       
flush();
       
sleep(2);
}

echo
"Done.";

ob_end_flush();

?>
up
9
php at stelio dot net
9 months ago
For a Windows system using IIS, the ResponseBufferLimit takes precedence over PHP's output_buffering settings. So you must also set the ResponseBufferLimit to be something lower than its default value.

For IIS versions older than 7, the setting can be found in the %windir%\System32\inetsrv\fcgiext.ini file (the FastCGI config file). You can set the appropriate line to:
  ResponseBufferLimit=0

For IIS 7+, the settings are stored in %windir%\System32\inetsrv\config. Edit the applicationHost.config file and search for PHP_via_FastCGI (assuming that you have installed PHP as a FastCGI module, as per the installation instructions, with the name PHP_via_FastCGI). Within the add tag, place the following setting at the end:
  responseBufferLimit="0"
So the entire line will look something like:
  <add name="PHP_via_FastCGI" path="*.php" verb="*" modules="FastCgiModule" scriptProcessor="C:\PHP\php-cgi.exe" resourceType="Either" responseBufferLimit="0" />
Alternatively you can insert the setting using the following command:
  %windir%\system32\inetsrv\appcmd.exe set config /section:handlers "/[name='PHP_via_FastCGI'].ResponseBufferLimit:0"
up
9
mandor at mandor dot net
5 years ago
This is what I use to turn off pretty much anything that could cause unwanted output buffering and turn on implicit flush:

<?php

   
@apache_setenv('no-gzip', 1);
    @
ini_set('zlib.output_compression', 0);
    @
ini_set('implicit_flush', 1);
    for (
$i = 0; $i < ob_get_level(); $i++) { ob_end_flush(); }
   
ob_implicit_flush(1);

?>

If it still fails though, keep in mind that Internet Explorer and Safari have a 1k buffer before incremental rendering kicks in, so you'll want to output some padding as well.
up
2
m@rco
10 years ago
in order to display in HTML pages something like a "progress bar" or if you want to force the web server to flush output to the browser, or the browser to flush as well, you can print a long enough "dummy" string to make the output buffer grow, as you probably know, like:

<?php
print "[";

for(
$i = 0; $i < 100; $i++){
 
$spaces.=" ";
}
// for

//and then

for($i = 0; $i < 10; $i++){
  for(
$ii = 0; $ii < 200000; $ii++){
   
//do something slow here
 
} // for
 
print "$spaces|";
 
flush();
}
// for

print "]";

/*
but this somethin may be not really what you expect in
a progress bar, as it prints spaces (although rendered as single by the browser) between the bar units..
you can solve this using
  $spaces.="<!-- bufferme -->";

/*

print "[";

for($i = 0; $i < 100; $i++){
  $spaces.="<!-- bufferme -->";
} // for

//and then

for($i = 0; $i < 10; $i++){
  for($ii = 0; $ii < 200000; $ii++){
    //do something slow here
  } // for
  print "$spaces|";
  flush();
} // for

print "]";

//which looks nice as a progress bar..
?>
up
5
MOELZE �T GMX DOt DE (Michael)
9 years ago
It is a bit complicated to work with the funktion flush() and you have to experiment with it a bit.
So if you design a site which has a timeloop at the end that calls a other site via a form data input (Data Submit) you have
to give something out to the buffer to get that new site loaden quick.

For example:

<?php
$instant
=gettimeofday();
$timenow=$instant["sec"];//Start Time

//timeloop(e.g. for security_save after 30 min)
while (1) { echo "<b></b>";//Useless (only to quickload next
                                    //or same Site when do a switch)
flush();                          //giveout buffer
$instant=gettimeofday();
$timeactual=$instant["sec"]; //get Actual Time in Secs
$flag=(($timeactual>$timenow+$diff)? 1:0);//$diff=switchTime
if ($flag) { what_do_at_switch_Time();//Sec.Save etc.etc.
$timenow=$timeactual; } //Set new Start Time
sleep(5); //Or so...(Important)
} //End of while-Loop
?>

So you can programm a security save or other function in your site and if you do a switch the upload of the new or same site (the called site) works...
up
4
seb dot field at gmail dot com
3 years ago
If flush() function does not work. You must set next options in php.ini like:

--[code]--
output_buffering = Off 
;output_handler =  
zlib.output_compression = Off 
;zlib.output_handler =  
--[^code^]--

If things does not work you must view headers from the server and check `Server` string.
In my case, as the frontend was Nginx webserver and Apache work as backend.
Accordingly, buffering must be disabled in Nginx config file.
To stop buffering you must add next string to config file:

--[code]--
proxy_buffering off;
--[^code^]--

and restart Nginx daemon.  More information about  configuration you find in documentation on the nginx website.
up
2
jason@jasonbaumgartner@info
5 years ago
Many of the suggestions below are very helpful but I would just like to clarify something. 

If you are making calls to a .php script with AJAX (xmlHttpReq) and use flush, this will send data to your script HOWEVER it will not set the xmlHttpReq.readyState to 4 -- which is a requirement to use the information sent (Firefox does however allow you to use the responseText property with a readyState == 3 but IE will throw an error).

To get around this, you will need to make sure of a couple things:

In your Apache php.ini config file, check to make sure that output buffering is disabled:

output_buffering = off

Next, disable gzip compression for the .php script that is called from your AJAX script by using the excellent suggestion from Mandor by placing the following at the top of your script:

@apache_setenv('no-gzip', 1);
@ini_set('zlib.output_compression', 0);

What causes this problem is that while the php child process is running under apache, apache is waiting for the script to complete before completely closing the connection.  Scripts that send information directly to the browser with echos and prints will get away with using flush followed by a sleep command and then clean up procedures.  However, if you notice in the status bar of your browser window, the connection is still held open by apache until the script completed ("Transferring" ... yadda yadda).

By turning off the Apache compression, the connection is terminated directly after a flush while still giving the user the ability to run a sleep command followed by clean up code.

This bit me because the AJAX was returning <img> tags to newly created images by php.  The cleanup script would then remove those images after completion. 

Since Apache held the connection open, the readyState only changed to 4 AFTER my php cleanup fired -- thereby erasing the links referred to my the <img> tags.

With this solution, the readyState will change to 4 BEFORE the sleep command begins.

I hope this saves someone a lot of time and frustration.  AJAX requests are an entirely different beast compared with simple outputting to a browser window.
up
2
Anonymous
8 years ago
In my testing, Internet Explorer 6.0 wouldn't flush anything nested in <table> or <td> tags, regardless of padding. But at the <body> level everything flushed with no fuss -- no padding or tags required.

Both Firefox 1.0 and Safari 2.0 could flush within tables, and both required a tag after the text (like <br>). Safari could flush only after the first 1024 characters where received. Firefox needed at least 8 characters per flush (but it could flush anything at the <body> level).

So the only thing that worked on all those browsers was this:

<html>
<body>
<?php  // not in table tags for IE
echo str_pad('',1024);  // minimum start for Safari
for ($i=10; $i>0; $i--) {
    echo
str_pad("$i<br>\n",8);
   
// tag after text for Safari & Firefox
    // 8 char minimum for Firefox
   
flush();  // worked without ob_flush() for me
   
sleep(1);
}
?>
</body>
</html>
up
1
chuck at artistan dot org
7 years ago
had problems flushing tables to screen.
this worked for me

<?php
if (ob_get_level() == 0) ob_start();
loop{
   
tables and stuff
   
echo str_pad("<br>\n",8);
}
ob_flush();
flush();  // needed ob_flush
usleep(50000);// delay minimum of .05 seconds to allow ie to flush to screen
?>
up
1
mbilliet at gmail dot com
7 years ago
Hello,

I had the same problems with sending a javascript after the <body></body> content has been sent to the browser (the script updates the content of an iframe).

Two solutions work for me:
   - add enough data (i.e.: extra dummy text like spaces) or,
   - echo the '</body>' tag at the end of the page

Note, that for the latter to work one should:
   - turn of output_buffering in php.ini and either:
      * turn on implicit_flush in its php.ini or,
      * call ob_implicit_flush(); at the beginning of a script

I preferr echoing the '</body>' tag at the end as it doesn't require any extra data to be sent over the wire and its much a neater coding technique.

Notes:
   - these worakarounds aren't needed when using perl and cgi,... .
   - you can leave the zlib.output_compression in your php.ini switched on

Kind regards and hoped this is of any help.

Maurits
up
1
crmacd at yahoo dot com
9 years ago
I figured out a way to create a simple progress bar that is for the most part cross platform. Seeing as I got my ideas from this site it's only share to give back to the community.

Note: Something interesting about browser buffering... you have to have the <html><body> for Firefox and some other browsers to recognize items by their id in Javascript. So I recommend using some sort of header function before calling this function.

<?php

function fn_progress_bar($intCurrentCount = 100, $intTotalCount = 100)
{
    static
$intNumberRuns = 0;
    static
$intDisplayedCurrentPercent = 0;
   
$strProgressBar = '';
   
$dblPercentIncrease = (100 / $intTotalCount);
   
$intCurrentPercent = intval($intCurrentCount * $dblPercentIncrease);
   
$intNumberRuns++;
       
    if(
1 == $intNumberRuns)
    {
       
$strProgressBar = <<< BAR
<table width='50%' id='progress_bar' summary='progress_bar' align='center'><tbody><tr>
<td id='progress_bar_complete' width='0%' align='center' style='background:#CCFFCC;'>&nbsp;</td>
<td style='background:#FFCCCC;'>&nbsp;</td>
</tr></tbody></table>
<script type='text/javascript' language='javascript'>
function dhd_fn_progress_bar_update(intCurrentPercent)
{
    document.getElementById('progress_bar_complete').style.width = intCurrentPercent+'%';
    document.getElementById('progress_bar_complete').innerHTML = intCurrentPercent+'%';
}
</script>
BAR;
    }
    else if(
$intDisplayedCurrentPercent <> $intCurrentPercent)
    {
       
$intDisplayedCurrentPercent = $intCurrentPercent;
       
$strProgressBar = <<< BAR
<script type='text/javascript' language='javascript'>
dhd_fn_progress_bar_update(
$intCurrentPercent);
</script>
BAR;
    }
    if(
100 <= $intCurrentPercent)
    {
       
$intNumberRuns = $intDisplayedCurrentPercent = 0;
       
$strProgressBar = <<< BAR
<script type='text/javascript' language='javascript'>
document.getElementById('progress_bar').style.visibility='hidden';
</script>
BAR;
    }
    echo
$strProgressBar;
   
flush();
   
ob_flush();
}

?>
up
1
Rusty
10 years ago
Netscape will flush the output as expected at the point it is called from within your script. IE, however, needs a boost.

IE seems to have a condition where it will flush data when it hits an end (</table>) tag AND has at least 256 chars of data.

So, pad your output with necessary spaces, wrap your progressing data around open (<table>) and end (</table>) tags, and then call flush() so that one script will work for Netscape as well.

TESTING ENVIRONMENT
IE: Ver/6.0.2800
Netscape: Ver/7.1
PHP: Ver/4.3.4
Apache: Ver/1.3.27
up
2
Mr.KTO
5 years ago
IE 7, Opera 9.6, any. All is quite simple. Today I just fogot what i do every night, :)

<?php
// All you need is 256 spaces first
echo str_repeat(" ", 256)."<pre>"; flush();

// and ANY TAG before \r\n
echo "working...<br/>\r\n"; flush(); sleep(1); // this in cycle
?>
up
2
mega023 at gmail dot com
8 years ago
If flush is not working probably mod_gzip is enabled.
To disable it just add following lines to .htaccess

<IfModule mod_gzip.c>
mod_gzip_on no
</IfModule>
up
2
matt at nospamplease dot hevanet dot com
9 years ago
Like IE, Safari needs a fair amount of data before it'll display anything, actually more than explorer.  The following code works for me in Firefox and Safari, and should work in IE as well.

<?php

for($i = 0; $i < 40000; $i++)
{
echo
' '; // extra spaces
}
// keeps it flowing to the browser…
flush();
// 50000 microseconds keeps things flowing in safari, IE, firefox, etc
usleep(50000);

?>

This code came from a comment on a blog discussing browser functionality with flush();
up
2
Kris
2 years ago
I had a bunch of problems trying to get flush working on my windows box, I finally found a solution after reading everyones here and it not working.

1) Set output_buffering = 0
2) Set zlib.output_compression = 0

I then used Wireshark to monitor network packets, and indeed the server was pusing the data, but the browser was not displaying it.. So it was a browser buffer issue (I am on Firefox 13)

For me I needed to send about 1k of data before it would display the data. To do this I added more header information..
In php.ini I set default_charset = "utf-8"
And that was enough to give me enough for the buffer issue.

You can also try doing
echo str_repeat(" ", 1024), "\n";
at the start of the script.

hope this helps
up
1
Alex
9 years ago
Modified progress bar.. Works in IE, Mozilla+FF.

<html>
<head>
<style type="text/css"><!--

div {
margin: 1px;
height: 20px;
padding: 1px;
border: 1px solid #000;
width: 275px;
background: #fff;
color: #000;
float: left;
clear: right;
top: 38px;
z-index: 9
}

.percents {
background: #FFF;
border: 1px solid #CCC;
margin: 1px;
height: 20px;
position:absolute;
width:275px;
z-index:10;
left: 10px;
top: 38px;
text-align: center;
}

.blocks {
background: #EEE;
border: 1px solid #CCC;
margin: 1px;
height: 20px;
width: 10px;
position: absolute;
z-index:11;
left: 12px;
top: 38px;
filter: alpha(opacity=50);
-moz-opacity: 0.5;
opacity: 0.5;
-khtml-opacity: .5
}

-->
</style>
</head>
<body>

<?php

if (ob_get_level() == 0) {
   
ob_start();
}
echo
str_pad('Loading... ',4096)."<br />\n";
for (
$i = 0; $i < 25; $i++) {
   
$d = $d + 11;
   
$m=$d+10;
   
//This div will show loading percents
   
echo '<div class="percents">' . $i*4 . '%&nbsp;complete</div>';
   
//This div will show progress bar
   
echo '<div class="blocks" style="left: '.$d.'px">&nbsp;</div>';
   
flush();
   
ob_flush();
   
sleep(1);
}
ob_end_flush();
?>
<div class="percents" style="z-index:12">Done.</div>
</body>
</html>
up
2
siggi AT june systems DOT com
9 years ago
After searching through the PHP site, google and various forums, not finding a solution to my script not outputting anything while calling flush and ob_flush, I thought of trying to tell PHP to call:

session_write_close();

before starting echo'ing. It worked like a charm. I couldn't find any references to this, so I hope this note will help someone in the future.
up
1
Arerano
5 years ago
This helped me getting flushing to work.
Using apache with deflate.

Turning compression off for this script: (add it somewhere at the top of the script)
apache_setenv('no-gzip', '1');

However, this only works if php is running as a module rather than a cgi-extension and safe mode must be disabled.

You can also turn the compression off for a directory by making a .htaccess file and adding the following entry:
mod_gzip_on Off

However that affects the whole directory.
Hope I could help.
up
1
Leon
7 years ago
I've spent days trying to figure out why flush didn't work all of a sudden, while it used to work perfectly. Apparently, it was McAfee Spamkiller that caused problems. Disabling it didn't work, I had to completely remove it. Hope this helps someone.
up
1
Kirk
7 years ago
If you're not explictly using the buffering functions, then ob_flush() is only necessary if output buffering is turned on in your php.ini file.

flush() is only necessary if implicit_flush is turned off in your php.ini file. Setting implicit_flush to on will remove the need for all these flush() calls, but it's generally only good in an extremely controlled environment. Turning on implicit_flush in a production environment can be bad.
up
1
no at spam dot com
7 years ago
ob_flush();flush();

Not the other way around, because it wont work.
up
1
mikael at oebb dot net
8 years ago
Hi all.
Been scratching my head over data NOT flushed to IE (6) even though I tried strpad 4096 chars, all headers OK,  TABLE and no TABLE, flush and ob_flush - still a blank page. Tried adding a sleep(1) before flushing - and everything worked as a charm. 

/Mikael
up
1
Marty
9 years ago
This is an extention of Rusty's comment below:

After sitting here for hours trying to make IE6 flush data out in the middle of a page (with it working perfectly in Firefox), I finally figured out the problem. IE will not display flushed data (even if it has it) unless the table that contains it is complete.

Every new element you want IE to display must not be in ANY kind of table at all. You must end all your tables.
up
1
Ghostshaw at spymac dot com
9 years ago
I would like to point out that there is a function to replace ob_flush and flush. If you set ob_implicit_flush(true); at the top of the page it will automatically flush any echo or print you do in the rest of the script.

Note that you still need a minimum amount of data to come through the browser filter. I would advice using str_pad($text,4096); since this automatically lenghtens the text with spaces to 4 KB which is the minimum limit when using FireFox and linux.

I hope this helps you all out a bit.
up
1
Squ1sher
9 years ago
On Windows xampp 1.3 with php 4.3.4 is use this functions
to force a flush.
<?php
function dummyErrorHandler ($errno, $errstr, $errfile, $errline) {
}

function
forceFlush() {   
   
ob_start();
   
ob_end_clean();
   
flush();
   
set_error_handler("dummyErrorHandler");
   
ob_end_flush();
   
restore_error_handler();
}
?>

ob_end_flush generates a warning, which is supressed, using the dummy-errorhander. You could also use @, but then nusphere will also print the warning.
up
0
Lucas
5 years ago
I just had some problems with flush() and ob_flush(). What I did to resolve this problem took me some time to figure out so I'd like to share what I came up with.

The main problem is the php setting "output_buffering" which can be set too large and will prevent your text from outputting. To change this value you can either set it in php.ini or you can add the line

php_value output_buffering "0"

to your .htaccess file. It will not work with ini_set() since it is PHP_INI_PERDIR.

Next thing is to begin with ob_start();
Then you need
ob_flush();
flush();
before any echo or print.

Your code might look like this:

<?php
ob_start
();

for(
$i=0;$i<70;$i++)
{
    echo
'printing...<br />';
   
ob_flush();
   
flush();

   
usleep(300000);
}

?>

Hope this helps anyone with the same problems.
up
0
vlad at modomail dot com
8 years ago
Sorry if this is off topic, but it's the closest place I could find :)  I had an issue with essentially running a CPU intensive task while updating the browser with a progress bar via javascript and flushing the buffer a lot.

When the script was running, it effectively blocked other pages from running.  I had a few extra httpd_preforks processes just waiting to be used, but they just sat there.  I wasn't reading a file, locking database tables or anything that I would suspect an exclusive lock on, just outputting a bunch of text to the browser.  I even tried throttling my loops to see if it was processor related but still had problems.

Finally, I found this in the php.ini file and changed the On to Off and it worked.

[Sockets]
; Use the system read() function instead of the php_read() wrapper.
sockets.use_system_read = Off

Posting in case someone else has the same issue (or if someone knows why this would make a difference :) ).
up
0
scottmacvicar at ntlworld dot com
10 years ago
Regarding Apache2
flush() will produce the same results as ob_flush() when output buffering is involved.
up
-2
David
6 years ago
mod_security 2.x core rules will also prevent flush() from working.
up
-4
macott[D0T]daiato[4T]gmail[D0T]com
7 years ago
If flush() don't work remember to check if you have any antivirus caching the data sent to the browser.
To Top