Recursion = Segmentation Fault?

budda

I'm currently running a dbase processing script i wrote which does some serious recursion and takes a log time to process things.

However i'm running in to some trouble sometimes. I get PHP crashing with segmentation fauls and it then dumps the memory space core file :mad:

My code is held in an objects method. my script creates an instance of the object and then calls 2 methods in it.

One of my methods is generating an array. Each element of the array contains an instance of an object. The object is used to store a few attributes from the database record.

In PHP what can cause segmentation faults? In my 'C' days it was always dodgy pointer access 😃 ... any clues as to what i could be doing in PHP? Is it just too much recursion? I don't have much control over the recursion as it varies.

I'm stuck. Anybody wanna make some suggestions? 🙂 Even different ways to approach a recursive problem are welcome...

Weedpacket

Well, from your description I can only hazard a guess or two.

If the recusion runs unchecked without bottoming out, then that will make PHP dump core.

Another possibility is if an object constructor contains a call to instantiate a new object of the same class (directly or indirectly) - you get an infinite loop with a new object being instantiated with every iteration with object A creating an object B creating an object C creating an object D ...... Barf. And quite quickly, as I recall...

What you describe does sound from here as if it could be done iteratively, though.

budda

My constructor is empty, so no recursive screw up there 🙂 I know the code is working as it will output stuff before the server rolls over and dies - i found out today from the sysadmin that the process was terminated because it ate too much memory. Hehe.

So, as an alternative I though about writing the values (objects) to a file rather than an array in memory. Then in my 2nd method re-read in the file a value (object) at a time and do the processing.

My question is.....

what is the best way to store an object on the hdd, and then read it back in?

I started with some code like this for saving:-

fwrite($file_store, serialize($readitem));

Where $readitem is an instance of a class. However how do I read JUST that value/object back in, when the file contains many of them one after another? The fread() function requires lengths to read in and I'm not going to know that.

Would simply writing an EOL after each fwrite() work, if i can somehow read data up to an EOL character later?

Maybe somebody has written a simple class to do this already? I've only briefly searched but found only one thing which stored everything in memory before writing it to a file at the end, which defeats my point in doing the whole file writing thing
🙁

Weedpacket

Well, OTTOMH writing a serialised object could work, using newlines to separate individual objects (assuming that serialise encodes \n characters...?)

Since it's a local file, you can use filesize() on it to get the entire size, so fgets($file_store,filesize($file_store)) will read in one line up to the next EOL or EOF (whichever comes first).

It means of course that to read the nth object, you'd have to first read the n-1st, but as this sounds like a pool dump, that may be what you want (though it's not like you have to keep the n-1st object after you read it...)

It's only a pity you can't store this preprocessed stuff in a database 🙂

budda

Originally posted by Weedpacket
Well, OTTOMH writing a serialised object could work, using newlines to separate individual objects (assuming that serialise encodes \n characters...?)

Just a thought over the weekend, but...
would i be okay forgetting about putting each serialized object on a newline? Thinking about it each serialized object should have some way to identify its start and end, right?

Since it's a local file, you can use filesize() on it to get the entire size, so fgets($file_store,filesize($file_store)) will read in one line up to the next EOL or EOF (whichever comes first).

Ths would be no good as it kinda defeats the purpose of writing to a file! I want to use the file so i can load an object at a time, just simple one after another process. This would keep memory usage down. Loading everything in at once killed the server after a bit 😃 it ran out of memory!

It means of course that to read the nth object, you'd have to first read the n-1st, but as this sounds like a pool dump, that may be what you want (though it's not like you have to keep the n-1st object after you read it...)

It's only a pity you can't store this preprocessed stuff in a database 🙂

I never opted for the database direction as it just seemed more hassle, i guess. i kinda assumed working with a simple temporary file to be a quick thang.

I'll hack on and see what I come up with.