I couldn't find any documentation about memory management of iOS. Especially about memory fragmentation. If you know any document about this, please let me know.
Memory fragmentation correction is an implementation detail. You should never, in any way, directly deal with it. However if you are worried that your objects will be moved around without notifying your code, don't; apple never moves objects - end of story. Once memory is allocated, it's yours (even if a framework class's instance is occupying it) until it is deallocated. That being said, from an academic perspective I see no reason why the iPhone shouldn't use at least a similar strategy to MacOS, on which there is an excellent article here.
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We have a a very large project which is basically an application which uses Linux Application programming and runs on PowerPC processor. This project was initially developed by another company. We acquired the project from the company and now we are maintaining the project.
The application is reported to have a lot of memory leak issue. Since this is a large project, it is not possible to go to each source code file and find out the memory leak. We have used Valgrid, mpatrol and other memory leak detection tools. These tools did not help much and the memory leak has not decreased by a significant percentage.
In this situation, how to go about to reduce the memory leak by a significant amount.Is there a general method which people use in these case to reduce the memory leak other than the memory leak detection tools like mentioned above.
Usually Valgrind belongs to the best tools for this tasks. If it does not work correctly, there might only be a couple of things you can still do.
First question: What language is the application in? Valgrind is very good for C and C++, but will not help you with garbage collected or scripting language. So check the language first. There might be something similar for java, but I have not used that much java, so you would have to ask someone else.
Play around a lot with the settings of valgrind. There are several plugins, that can help with this. One example could be using --leak-check=full or similar options. There are also plugins for valgrind, that can enhance it detection capabilities.
You say, that the application was reported to have a memory leak. How was this detected? Did the application detect this by itself. If it was detected by the application on it's own without any external tools, this probably means someone has added their own memory tracker inside the application. Custom memory tracker, memory pools etc. mess up valgrind and any other leak detection system very bad. So in case any custom memory handling is present in the application, your only choice is to either deactivate it (if possible) or to hook into this custom mechanism. How this could be done depends on your application only.
Add your own memory tracker. For example in C++ it is possible to hook into new/delete calls and get them to track the memory. There are a couple of libraries you can use for this. You can also write your own new/delete replacement in about 500 LOC. If you decide to use this method, be sure to read a lot of tutorials on replacing new/delete, since there are several things that are unusual in the C++ world when attempting this task.
What makes you so sure, there is an memory leak in the application (i.e. how was this detected)? If a tool just reported huge numbers of allocated memory, this might not even mean, there is an actual memory leak. A memory leak means that the handles to the memory are lost and hence it becomes impossible to every reach and free that memory again. In case your application just get's a lot of memory and keeps it accessible, you probably have a completely different problem. For example you simply might use an algorithm with a bad space complexity at one point or the other, leading to many allocations. In this case you will not need a leak detector, but rather a memory profiler, which gives you more detailed overview of the memory footprint of the code parts. However I have never used a profiler for this kind of task before, so I cannot give you any more hints on this.
You could replace all memory allocation calls with calls to your own allocation methods, which should call original methods and at the same time count memory usage and where it was allocated. This will allow you to find the leaks and eliminate them by hand.
There might also be automated tools that allow you to do this - not sure, haven't used any. But this method works.
Perhaps you might also consider using Boehm's garbage collector (that is using GC_malloc instead of malloc etc... and not bother about free-ing data).
I am getting started in working with Windows CE to utilize RTOS to reduce latency concerns with interrupts and threads and USB. What class-libraries(visual c++) can you point me to that would be good to have learned well to speed up the learning curve?
Thanks
That's a really, really broad question. The most important piece of advice I'll give you is that if you're after determinism and speed (your reference to an RTOS leads me to think you consider these important) then you need to be aware that any memory allocation or deallocation in a piece of code makes it non-deterministic.
C++ classes often have allocations and deallocations buried in them, so whatever you choose (and whatever you write), use them wisely. Sometimes they'll allow you to provide custom allocators (e.g. Boost) which you can use to just pull memory from an already allocated heap you create somewhere.
Keep the real-time parts of the code as small and simple as possible.
The GLib docs recommend use of the GLib Slice Allocator over malloc:
"For newly written code it is recommended to use the new g_slice API instead of g_malloc() and friends, as long as objects are not resized during their lifetime and the object size used at allocation time is still available when freeing."
-- http://developer.gnome.org/glib/unstable/glib-Memory-Slices.html
But in practise is g_slice significantly faster than Windows/Linux malloc(faster enough to warrant the extra trouble of handling sizes and GLib's preprocessor hacks like g_slice_new)? I'm planning to use GLib in my C++ program to handle INIish configuration (GKeyFile) and to get access to data structures not available in C++ like GHashTable, so the GLib dependency doesn't matter anyway.
Faster enough to be worth it sort of depends on your app. But they should be faster.
There is another issue besides speed, which is memory fragmentation and per-block overhead. GSlice
leaves malloc to deal with large or variable-size allocations while handling small known-size objects more space-efficiently.
Slice API heavily borrows from research conducted by Sun Microsystems in 1980s and it was called slab allocation back then. I could not find original research paper but here is a wikipedia page about it or you can just google for "slab allocation".
Essentially it eliminates expensive allocation/deallocation operations by facilitating reuse of memory blocks. It also reduces or eliminates memory fragmentation. So it is not all about speed, even though it should improve it as well.
If you should used or not - it depends... Look at Havoc's answer - he summarized it pretty well.
Update 1:
Note, that modern Linux kernels include SLAB allocator as one of the option and it is often the default. So, the difference between g_slice() and malloc() may be unnoticeable in that case. However, purpose of glib is cross-platform compatibility, so using slice API may somewhat guarantee consistent performance across different platforms.
Update 2:
As it was pointed by a commenter my first update is incorrect. SLAB allocation is used by kernel to allocate memory to processes but malloc() uses an unrelated mechanism, so claim that malloc() is equivalent to g_slice() on Linux is invalid. Also see this answer for more details.
My .NET application has memory leak. Few people seem to recommend using CLR Profiler for this pupose I am a bit lost on the idea. To me in order to find a memory leak, tool should compare two memory states that can give you statistics like growth in objects between two states. So in my mind, if a tool cannot compare two (or more) memory states, it cannot be used for detecting memroy leak. Obviously things like performance counters is bit different concept where you can trend the memory usage.
So my question is really if someone can explain how exactly CLR Profiler can be used to detect memory leaks?
Well it depends on what kind of memory leak you have.
We had a reproducible one, where we new that a certain chain of events should always leave a clean table after work was done - but it wasn't.
So we simple setup a test where we did it a couple of thousand times - then we looked at those objects (bigger in number) in the heap graph and at the "root"-object the cause of why the objects where still alive. It helped to solve our problem...
In the following SO question, it is mentionned that the Garage Collector was not included in iOS in order to conserve battery power.
Is there an offical reference from Apple stating that battery life is one of the reasons why a Garbage Collector was not included inside iOS?
I have been looking for it on google but was not able to find anything relevant.
... stating that battery life is one of the reasons why a Garbage Collector was not included inside iOS?
I would call that either good PR or agressive fanboyism. A good GC adds little overhead, especially no amount of overhead anyone would have to be concerned about. Problem is that Apple doesn't have a good garbage collector.
Objective-C's garbage collector is conservative and doesn't do compaction, which means that applications will leak memory over time and if you have a long-running app on your phone it will eventually eat up all available memory and crash. Actually that's the reason Apple recommends not using it for long-running tasks even on Mac OS X.
There is definitely also a major problem with unpredictable performance on all limited resouce devices. A colleague and mine were hired by Intel for the Pentim 3 launch to make some hefty UI stuff that showcased the AWESOME power of this processor so that everybody would upgrade.
For some reaon it was decided that a Java-based 3D interface to the Excite search engine was the ultimate solution. Planets with moons would represent result pages and individual search results. Space age stuff. This was obviously before the big internett ka-blam when people had way too much money and grand vision of a 3D cyberworld.
Well, the garbageman always popped in at the wrong time and frequently, so we did what we had to do back then and ask for a ton of memory and write our own allocation stuff. The client had no tolerance for jumpy GFX.
That did the trick, dirty as it may seem today.
I maintain that Apple's decision has most to do with little memory availabe plus wanted optimal, even speed in apps and games. They are not the kind of people who are happy with people going "argh, now it˙s lagging again."
I refer you to the recent hooplah around 4.x being dog slow on some devices. The new update kicked out some features to trade off for performance.