This week while I was awaiting for a new project confirmation I saw myself doing some code fixing for another project, that's something quite common and I really don't mind that. One of my tasks was to develop a little page to upload images to a server. That's not a problem, so I decided to try something new. Yes, I was very keen to use Silverlight for the task, but I used some good old javascript and a very cool concept similar to the called bubbling events, which is basically to raise an event from a determined and let it propagate up in the chain until it is captured.
My first idea was : I will create a web user control that can be easily added to a common web page and this guy will pass the list like a bubbled event.
This control will implement an interface to select and hold a list of files and will be able to send that list to the page and notify the page the list is ready to upload. Let's call it MyUpload control.
being a user control any programmer can then drag and drop this guy to any page and it must be atomic enough to not be too attached to the parent. So it inherits from usercontrol, and will have, at least for now, 2 methods called upload and a click. Here the things are getting cool. This click event is an event raiser.
When a programmer use this control, by calling the click method it will pass the selected file collection to the page. How? sending the list as arguments of the call.
The upload method must then be responsible populate the list and send this list to the caller.
Once the event is triggered in the webpage this page will loop through the items in the received file list and for each instance I will 'save file as...' and provide the path in the web server directory. This will move the file to the desired location as specified in the document request.
Could I save the files in the database? Yes, I could but all the specs for the task are done and that was the mission. So I won't discuss any matters of a better solution for this given scenario.
My upload control will have two buttons add and remove files which will be responsible for maintaining the list of files I want to upload. Why is that? because we want to upload a list of files in one shot and not one by one. Indeed, I'll spend more hours implementing this solution but at the end this will be a reusable control and as I said, any other programmers will then just drag and drop it should they need to implement a similar solution.
How do implement the code for add and remove files? That's the most difficult part and requires a good amount of javascript knowledge. Just this javascript routine can be subject of a post by itself. For now let's say the control has a private method called buildjavascript which renders in the page all the javascript methods necessary to maintain this object list.
Returning to our code behind, this list will be a collection and the best way to keep it and pass it by posting is to make it inherit from a very cool and useful class for this situation: the HttpFileCollection.
The upload button in the control will call the upload method which does nothing but raise the event to the page. The page who has the control implements already the method expected to parse the list as an HttpFileCollection object. Now, we only have to save the object as new name, being in a new location.
My initial design is done and I am doing the javascript side of things. This week was hectic but once things come back to normality and some time is left for me, I will share my code here somewhere.
See you later.
Here an interesting case. Consider there 2 scenarios:
Both are running the same website, both have the same amount of users connected.
Now imagine this website has a page to upload pictures, just like any regular photo-album website.
For some reason, at some point the users complain that they see an error page indicating out of memory error.
So, you wonder: How come? they are just uploading a photo to my website, and I still have plenty of memory in my server anyway.
Anyhow, you stop thinking about this and go for the easiest, quick and dirty solution: If the system tells me that my computer does not have enough memory then I just need to add more memory. Right?
And guess what? you still will get the error message.
That's a very common mistake. Having a machine with 10GB of memory does not mean you will have 10GB of memory available. I explain.
It does not matter if your computer or server has 512 MB, 1 GB, 2 GB, 4 GB or 8 GB of RAM. If your machine is a 32-bit machine it will only be able to see/manage 4 GB. That's mathematics, that's life, that's the way things are and you can't do nothing about it. A 32-bit machine can not do more than that.
Additional memory may increase your system performance, but it won't increase the memory availability. Sure your computer will use less the hard disk for swapping operations and will be able put more stuff in memory and start some programs faster, but 4GB is the limit; after this point the memory management module will start doing disk swap and to use the famous page file.
And here comes more bad news: Your Windows system on a 32-bit machine requires 2 GB allocated only for it.
So, if you have 4 GB installed, effectively you will have 2 GB only for applications; your windows will be using alone 2 GB.
So, what does out of memory means?
Well, according to some people at Microsoft, this limit for an average configuration is reached between 600 MB and 800 MB of utilization. That 800 number is NOT A RULE, is a baseline. Generally speaking the largest majority of configurations with website, .NET and SQL Server database might have a problem around this point. Of course, this can vary from system to system...as a matter of fact a system can be out of memory at just 600 MB.
Yes, it does sounds crazy. You look so happy now that you just bought a 4GB RAM notebook and your computer is breaking with just 800MB, hun?
Here is another point for you. Have you ever seen someone bragging that he/she bought a 10-megapixel camera and now he/she believes their pictures are going to be better because of this?
Well, guess what? Just like the number of megapixels in a camera box does not have much to do with picture quality, RAM memory does not have much to do with hard disk space.
That's a common mistake: People buy RAM as if they were buying a hard disk.
RAM usage needs to me continuous, unlike hard disk. A simple 5MB Microsoft Word document when saved in a hard disk can be split up in hundreds of pieces; When you open this file in memory, the RAM requires those 5MB to be allocated continuously.
Can you see now the reason for the 'out of memory' message?
Yes, it really means 'there is not enough continuous memory to place that file in memory'. Your system might have 2GB of RAM but unfortunately it might be too busy with stuff running and there is no enough continuous memory to put the picture you are uploading.
Yeah, you can not do much but you can buy a 64-bit machine then when you add more memory you can really use it more efficiently. And yes, we have Microsoft Windows systems for 64-bit machines.
If you do not want to buy a new system of upgrade you current server to a better version then you should think other solutions in the business process, such as to avoid users upload pictures with more than 1 MB in size to be uploaded.
See you later.