First, it’s platform dependent. In some architectures, stack is allocated from the bottom of the address space and grows upwards. Assuming an architecture like x86 that stack grown downwards from the top of address space, the idea is pretty simple: =============== Highest Address (e.g. 0xFFFF) | | | STACK | | | |————-| <- Stack … Read more
Since we have a virtual address space of 2^32 and each page size is 2^12, we can store (2^32/2^12) = 2^20 pages. Since each entry into this page table has an address of size 4 bytes, then we have 2^20*4 = 4MB. So the page table takes up 4MB in memory.
I have found the answer to my question myself:) So what I didn’t understand was how the glibc could differentiate between a Segfault and a corrupted double-linked list, because according to my understanding, from perspective of glibc they should look like the same thing. Because if I implement a double-linked list inside my program, how … Read more
Try using the getconf utility, which will allow you to retrieve the page size, in bytes, easily. getconf PAGESIZE Example output, in bytes: 4096
When people talk about sequential vs random writes to a file, they’re generally drawing a distinction between writing without intermediate seeks (“sequential”), vs. a pattern of seek-write-seek-write-seek-write, etc. (“random”). The distinction is very important in traditional disk-based systems, where each disk seek will take around 10ms. Sequentially writing data to that same disk takes about … Read more
Memory level warnings are logged by SpringBoard. As an app developer you don’t need to care about it. Just responding to -{application}didReceiveMemoryWarning is enough. There are 4 levels of warnings (0 to 3). These are set from the kernel memory watcher, and can be obtained by the not-so-public function OSMemoryNotificationCurrentLevel(). typedef enum { OSMemoryNotificationLevelAny = … Read more
This has been a big concern for some using Node.js, and there are good news. The new memory limit for V8 is now unknown (not tested) for 64bit and raised to as much as 32bit address space allows in 32bit environments. Read more here: http://code.google.com/p/v8/issues/detail?id=847
The autoreleasepool pattern is used in Swift when returning autorelease objects (created by either your Objective-C code or using Cocoa classes). The autorelease pattern in Swift functions much like it does in Objective-C. For example, consider this Swift rendition of your method (instantiating NSImage/UIImage objects): func useManyImages() { let filename = pathForResourceInBundle for _ in … Read more
The difference is that an object will be deallocated as soon as there are no strong pointers to it. Even if weak pointers point to it, once the last strong pointer is gone, the object will be deallocated, and all remaining weak pointers will be zeroed out. Perhaps an example is in order. Imagine our … Read more
Softwares run on the OS on a very simple premise – they require memory. The device OS provides it in the form of RAM. The amount of memory required may vary – some softwares need huge memory, some require paltry memory. Most (if not all) users run multiple applications on the OS simultaneously, and given … Read more