Re: Pointers For Newbies, Reminders For Oldies

On Sat, 2010-01-30 at 13:02 +1100, clancy_1@cybec.com.au wrote: > On Thu, 28 Jan 2010 10:02:56 -0500, robert@interjinn.com (Robert Cummings) wrote: > > > >I don't know what you guys are doing wrong but the following should be > >the correct behaviour: > > > ><?php > > > >function get_memory( $init=false ) > >{ > > static $base = null; > > if( $base === null || $init ) > > { > > $base = memory_get_usage(); > > } > > > > return memory_get_usage() - $base; > >} > > > >function simple_access( $data ) > >{ > > $foo = $data[100]; > > echo 'Memory: '.get_memory().' (simple access)'."\n"; > >} > > > >function foreach_value_access( $data ) > >{ > > foreach( $data as $value ) > > { > > $foo = $value; > > break; > > } > > echo 'Memory: '.get_memory().' (foreach value > > access)'."\n"; > >} > > > >function foreach_key_access( $data ) > >{ > > foreach( $data as $key => $value ) > > { > > $foo = $key; > > $foo = $value; > > break; > > } > > echo 'Memory: '.get_memory().' (foreach key/value > > access)'."\n"; > >} > > > >function modify_single_access( $data ) > >{ > > $data[100] = str_repeat( '@', 10000 ); > > echo 'Memory: '.get_memory().' (modify single > > access)'."\n"; > >} > > > >function modify_all_access( $data ) > >{ > > for( $i = 0; $i < 1000; $i++ ) > > { > > $data[$i] = str_repeat( '@', 10000 ); > > } > > > > echo 'Memory: '.get_memory().' (modify all > > access)'."\n"; > >} > > > > > >get_memory( true ); > > > >$data = array(); > >for( $i = 0; $i < 1000; $i++ ) > >{ > > $data[$i] = str_repeat( '#', 10000 ); > >} > > > >echo 'Memory: '.get_memory().' (data initialized)'."\n"; > > > >simple_access( $data ); > >foreach_value_access( $data ); > >foreach_key_access( $data ); > >modify_single_access( $data ); > >modify_all_access( $data ); > > > >?> > > > >I get the following output (PHP 5.2.11 from command-line): > > > > Memory: 10160768 (data initialized) > > Memory: 10161008 (simple access) > > Memory: 10161104 (foreach value access) > > Memory: 10161240 (foreach key/value access) > > Memory: 10267312 (modify single access) > > Memory: 20321576 (modify all access) > > > >I don't double up on memory consumption until I force the write onto > >every element... this is expected because internally every array element > >is individually subject to the Copy-On-Write (COW) principle since each > >element is internally stored as a zval just like the array itself. > > Thanks for this. I was just revising a bit of code to insert some extra entries into an > array. Previously I had opened a new array, copied the data up to the insertion point into > it, put in the new entry, then copied the tail, then renamed the new array. After reading > this, I realise the correct procedure was to copy the existing data into a temporary > array, insert the new entry in the existing array, and then copy the tail from the copy > back into the working data. > > This way only the data in the tail actually has to be copied, rather than the whole array. > Erm, what about array_splice()? You can use that to insert items into an array at any point you want. Thanks, Ash http://www.ashleysheridan.co.uk