I recently used the gem5 emulator, which is a system emulator. I have encountered terms such as PUTS PUTS GETS GETX in memory access. What do these terms mean in memory access? Can someone help me? Can you explain it to me in detail?
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I have just gotten into programming and i realized for every variable that you identify, you use ur computer memory as it is saved in it somewhere.
I wanted to know if I run a piece of code multiple times, would I lose more memory or somehow once you close terminal or program, system deletes it automatically.
THANK YOU
I've run a code several times and every time the address that a same variable is saved in is different.
I believe I'm wasting my computers memory so if I am how do I delete said variables from memory?
Yes, for all intents and purposes, it is gone the second the program has finished executing.
There are times that this isn't true, but they almost certainly don't apply to you. When on a normal computer or OS running device, the OS (operating system) will clean-up any resources used by your code when it is finished running. This includes all the memory used by declared variables (which is tiny amounts anyway, normally), files you have opened and forgotten to close, and pretty much everything else. OSs are very resilient!
I've run a code several times and every time the address that a same variable is saved in is different. I believe I'm wasting my computers memory so if I am how do I delete said variables from memory?
These are some pretty good investigative skills (a good sign for someone new to programming), but there are different reasons for this, don't worry. Memory addresses are a complex topic that is worth a look at later down the line, but the simplified story is that memory addresses are different every time you run the program for both security and performance reasons.
I'm working on a Mac app. Initially monitoring Xcode's memory report while I ran my app showed showed the memory was just ramping up crazy. I used Instruments and profiled my app for allocations and leaks. Turned out there wasn't much leaked memory as you would expect due to strong reference cycles etc. However there was a lot of abandoned memory. By following the stack trace that lead to my code I have fixed by 70% using autorelease pools etc. Still the remaining 30% of abandoned memory seems to point system calls.
Now I have two questions based on that I have two questions
1) I want to fix the remaining 30%. How can I get rid of abandoned memory? I have already used Instruments and know exactly where those system calls are spawned but still dont know what to do to have that memory be cleaned up. (using ARC no manual retain/ release and autorelease doesn't seem to make a diff.)
2) After I know whatever my application was doing has completed and there is no need for any memory to be there (just like the application first started) I want to get rid of all memory that my app has used up. This I plan to use as a brute force approach to clean up all memory just like the system would if the user closes the app or turns off the system.
Basically if I know where my apps memory is in the file system I'll just programmatically call purge command on that or something similar. Because at this point I'm 100% sure nothing needs to be in memory for the app except for the first screen that you would expect the first time you launch the app.
I read this, this, this and this but they weren't helpful.
I am migrating a code from Linux to Vxworks. The code requires opening physical/main memory and then map the physical to virtual memory using mmap.
In Linux, main memory is accessed by
fd = open("/dev/mem", O_RDONLY);
Can you please let me know how this can be accomplished in Vxworks.
Thanks in advance
It depends on which programming environment your migrated code will be running.
For kernel mode, it is much easier as generally you can access everywhere in the system memory in read-only mode as long as its memory region is mapped in the page table. No special API is needed in your code to access the memory.
For user mode (aka Real Time Process, only available starting from VxWorks 6.0), things are a little bit complicated. You need write a pair of code blocks, with one operating in the kernel mode while the other one in the user mode. Please refer to the comment block in the VxWorks source codes for a code example # vxworks-6.9/target/usr/src/os/mm/devMemLib.c (taking VxWorks 6.9 for example).
I want to plot a larger amount of data within an metro application and I need to buffer this. To find out how far I can buffer it would be great to know how much memory is still available (to my app), this shouldn't inlclude virtual memory.
Is there any way in a metro app to get this Information? I only found GlobalMemoryStatusEx, but that can only be used in desktop apps
Thank you
I just had to deal with this and got hold of the right people at Microsoft to answer this. Unfortunately the answer was : No you can't do that, except use the restricted calls that you found but using those prevents you from getting certified for publication in the store.
How about just trying to allocate a lot of memory in chunks. When it first fails - add up the sizes of the chunks and either release them or use them for your operations.
I recently I came across an error that I cannot understand. The game I'm developing using Cocos2D just freezes at a certain random point -- it gets a SIGSTOP -- and I cannot find the reason. What tool can I use (and how do I use it) to find out where the error occurs and what's causing it?
Jeremy's suggestion to stop in the debugger is a good one.
There's a really quick way to investigate a freeze (or any performance issue), especially when it's not easy to reproduce. You have to have a terminal handy (so you'll need to be running in the iOS simulator or on Mac OS X, not on an iOS device).
When the hang occurs pop over to a terminal and run:
sample YourProgramName
(If there are spaces in your program name wrap that in quotes like sample "My Awesome Game".) The output of sample is a log showing where your program is spending time, and if your program is actually hung, it will be pretty obvious which functions are stuck.
I disagree with Aaron Golden's answer above as running on a device is extremely useful in order to have a real-case scenario of where the app freezes. The simulator has more memory and does not reproduce the hardware of the device in an accurate way (for example, the frame rate is in certain cases lower).
"Obviously", you need to connect your device (with a developer profile) on Xcode and look at the console terminal to look for traces that user #AaronGolden suggested.
If those are not enough you might want to enable a general exception breakpoint in Xcode to capture more of the stacktrace messages.
When I started learning Cocos2D my app often frooze. This is a list of common causes:
I wasn't using sprite sheets and hence the frame rate was dropping drammatically
I was using too much memory (too many high-definition sprites. Have a look at TexturePacker and use pvr.ccz or pvr.gz format; it cuts memory allocation in half)
Use instruments to profile your app for memory warnings (for example, look at allocation instruments and look for memory warnings).