memory interview questions
Top memory frequently asked interview questions
How can I find the memory used on my Android application, programmatically?
I hope there is a way to do it. Plus, how do I get the free memory of the phone too?
Source: (StackOverflow)
I’m currently monitoring a Java application with jconsole. The memory tab lets you choose between:
Heap Memory Usage
Non-Heap Memory Usage
Memory Pool “Eden Space”
Memory Pool “Survivor Space”
Memory Pool “Tenured Gen”
Memory Pool “Code Cache”
Memory Pool “Perm Gen”
What is the difference between them ?
Source: (StackOverflow)
I have a list view with a couple of image buttons on each row. When you click the list row, it launches a new activity. I have had to build my own tabs because of an issue with the camera layout. The activity that gets launched for result is a map. If I click on my button to launch the image preview (load an image off the SD card) the application returns from the activity back to the listview activity to the result handler to relaunch my new activity which is nothing more than an image widget.
The image preview on the list view is being done with the cursor and ListAdapter. This makes it pretty simple, but I am not sure how I can put a resized image (I.e. Smaller bit size not pixel as the src for the image button on the fly. So I just resized the image that came off the phone camera.
The issue is that I get an out of memory error when it tries to go back and re-launch the 2nd activity.
- Is there a way I can build the list adapter easily row by row, where I can resize on the fly (bit wise)?
This would be preferable as I also need to make some changes to the properties of the widgets/elements in each row as I am unable to select a row with touch screen because of focus issue. (I can use roller ball.)
- I know I can do an out of band resize and save of my image, but that is not really what I want to do, but some sample code for that would be nice.
As soon as I disabled the image on the list view it worked fine again.
FYI: This is how I was doing it:
String[] from = new String[] { DBHelper.KEY_BUSINESSNAME,DBHelper.KEY_ADDRESS,DBHelper.KEY_CITY,DBHelper.KEY_GPSLONG,DBHelper.KEY_GPSLAT,DBHelper.KEY_IMAGEFILENAME + ""};
int[] to = new int[] {R.id.businessname,R.id.address,R.id.city,R.id.gpslong,R.id.gpslat,R.id.imagefilename };
notes = new SimpleCursorAdapter(this, R.layout.notes_row, c, from, to);
setListAdapter(notes);
Where R.id.imagefilename is a ButtonImage.
Here is my LogCat:
01-25 05:05:49.877: ERROR/dalvikvm-heap(3896): 6291456-byte external allocation too large for this process.
01-25 05:05:49.877: ERROR/(3896): VM wont let us allocate 6291456 bytes
01-25 05:05:49.877: ERROR/AndroidRuntime(3896): Uncaught handler: thread main exiting due to uncaught exception
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): java.lang.OutOfMemoryError: bitmap size exceeds VM budget
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.graphics.BitmapFactory.nativeDecodeStream(Native Method)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.graphics.BitmapFactory.decodeStream(BitmapFactory.java:304)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.graphics.BitmapFactory.decodeFile(BitmapFactory.java:149)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.graphics.BitmapFactory.decodeFile(BitmapFactory.java:174)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.graphics.drawable.Drawable.createFromPath(Drawable.java:729)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.widget.ImageView.resolveUri(ImageView.java:484)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.widget.ImageView.setImageURI(ImageView.java:281)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.widget.SimpleCursorAdapter.setViewImage(SimpleCursorAdapter.java:183)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.widget.SimpleCursorAdapter.bindView(SimpleCursorAdapter.java:129)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.widget.CursorAdapter.getView(CursorAdapter.java:150)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.widget.AbsListView.obtainView(AbsListView.java:1057)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.widget.ListView.makeAndAddView(ListView.java:1616)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.widget.ListView.fillSpecific(ListView.java:1177)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.widget.ListView.layoutChildren(ListView.java:1454)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.widget.AbsListView.onLayout(AbsListView.java:937)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.view.View.layout(View.java:5611)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1119)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.widget.LinearLayout.layoutHorizontal(LinearLayout.java:1108)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.widget.LinearLayout.onLayout(LinearLayout.java:922)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.view.View.layout(View.java:5611)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.widget.FrameLayout.onLayout(FrameLayout.java:294)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.view.View.layout(View.java:5611)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1119)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.widget.LinearLayout.layoutVertical(LinearLayout.java:999)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.widget.LinearLayout.onLayout(LinearLayout.java:920)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.view.View.layout(View.java:5611)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.widget.FrameLayout.onLayout(FrameLayout.java:294)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.view.View.layout(View.java:5611)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.view.ViewRoot.performTraversals(ViewRoot.java:771)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.view.ViewRoot.handleMessage(ViewRoot.java:1103)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.os.Handler.dispatchMessage(Handler.java:88)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.os.Looper.loop(Looper.java:123)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at android.app.ActivityThread.main(ActivityThread.java:3742)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at java.lang.reflect.Method.invokeNative(Native Method)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at java.lang.reflect.Method.invoke(Method.java:515)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:739)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:497)
01-25 05:05:49.917: ERROR/AndroidRuntime(3896): at dalvik.system.NativeStart.main(Native Method)
01-25 05:10:01.127: ERROR/AndroidRuntime(3943): ERROR: thread attach failed
I also have a new error when displaying an image:
01-25 22:13:18.594: DEBUG/skia(4204): xxxxxxxxxxx jpeg error 20 Improper call to JPEG library in state %d
01-25 22:13:18.604: INFO/System.out(4204): resolveUri failed on bad bitmap uri:
01-25 22:13:18.694: ERROR/dalvikvm-heap(4204): 6291456-byte external allocation too large for this process.
01-25 22:13:18.694: ERROR/(4204): VM won't let us allocate 6291456 bytes
01-25 22:13:18.694: DEBUG/skia(4204): xxxxxxxxxxxxxxxxxxxx allocPixelRef failed
Source: (StackOverflow)
Under Linux, how do I find out which process is using the swap space more?
Any scripts/links appreciated..
Source: (StackOverflow)
Could someone possibly give an example of "cache unfriendly code" and the "cache friendly" version of that code?
How can I make sure I write cache-efficient code?
Source: (StackOverflow)
How do I determine the size of my array in C?
That is, the number of elements the array can hold?
Source: (StackOverflow)
I'm currently building a Java app that could end up being run on many different platforms, but primarily variants of Solaris, Linux and Windows.
Has anyone been able to successfully extract information such as the current disk space used, CPU utilisation and memory used in the underlying OS? What about just what the Java app itself is consuming?
Preferrably I'd like to get this information without using JNI.
Source: (StackOverflow)
I am keen to look into Scala, and have one basic question I cant seem to find an answer to:
in general, is there a difference in performance and usage of memory between Scala and Java?
Source: (StackOverflow)
Is the memory space consumed by one object with 100 attributes the same as that of 100 objects, with one attribute each?
How much memory is allocated for an object?
How much additional space is used when adding an attribute?
Source: (StackOverflow)
What does the register keyword do in C language? I have read that it is used for optimizing but is not clearly defined in any standard. Is it still relevant and if so, when would you use it?
Source: (StackOverflow)
I want to know the size occupied by a JavaScript object.
Take the following function -
function Marks()
{
this.maxMarks = 100;
}
function Student()
{
this.firstName = "firstName";
this.lastName = "lastName";
this.marks = new Marks();
}
Now.. i instantiate the student
var stud = new Student();
so that I can do stuff like
stud.firstName = "new Firstname";
alert(stud.firstName);
stud.marks.maxMarks = 200;
etc...
now, stud object will occupy some size in memory. It has some data and more objects.
How do I find out how much memory the stud object occupies?
something like a sizeof() in JavaScript?
It would be really awesome if i could find it out in a single function call like
sizeof(stud)
P.S. I've been searching the Internet for months - couldn't find it (asked in a couple of forums - no replies).
Source: (StackOverflow)
I've run into memory leaks many times. Usually when I'm malloc-ing like there's no tomorrow, or dangling FILE *s like dirty laundry. I generally assume (read: hope desperately) that all memory is cleaned up at least when the program terminates. Are there any situations where leaked memory won't be collected when the program terminates, or crashes?
If the answer varies widely from language-to-language, then let's focus on C(++).
Please note hyperbolic usage of the phrase, 'like there's no tomorrow', and 'dangling ... like dirty laundry'. Unsafe* malloc*ing can hurt the ones you love. Also, please use caution with dirty laundry.
Source: (StackOverflow)
Should you set all the objects to null (Nothing in VB.NET) once you have finished with them?
I understand that in .NET it is essential to dispose of any instances of objects that implement the IDisposable interface to release some resources although the object can still be something after it is disposed (hence the isDisposed property in forms), so I assume it can still reside in memory or at least in part?
I also know that when an object goes out of scope it is then marked for collection ready for the next pass of the garbage collector (although this may take time).
So with this in mind will setting it to null speed up the system releasing the memory as it does not have to work out that it is no longer in scope and are they any bad side effects?
MSDN articles never do this in examples and currently I do this as I cannot
see the harm. However I have come across a mixture of opinions so any comments are useful.
Source: (StackOverflow)
I want to create a program that will simulate an out-of-memory (OOM) situation on a Unix server. I created this super-simple memory eater:
#include <stdio.h>
#include <stdlib.h>
unsigned long long memory_to_eat = 1024 * 50000;
size_t eaten_memory = 0;
void *memory = NULL;
int eat_kilobyte()
{
memory = realloc(memory, (eaten_memory * 1024) + 1024);
if (memory == NULL)
{
// realloc failed here - we probably can't allocate more memory for whatever reason
return 1;
}
else
{
eaten_memory++;
return 0;
}
}
int main(int argc, char **argv)
{
printf("I will try to eat %i kb of ram\n", memory_to_eat);
int megabyte = 0;
while (memory_to_eat > 0)
{
memory_to_eat--;
if (eat_kilobyte())
{
printf("Failed to allocate more memory! Stucked at %i kb :(\n", eaten_memory);
return 200;
}
if (megabyte++ >= 1024)
{
printf("Eaten 1 MB of ram\n");
megabyte = 0;
}
}
printf("Successfully eaten requested memory!\n");
free(memory);
return 0;
}
It eats as much memory as defined in memory_to_eat which now is exactly 50 GB of RAM. It allocates memory by 1 MB and prints exactly the point where it fails to allocate more, so that I know which maximum value it managed to eat.
The problem is that it works. Even on a system with 1 GB of physical memory.
When I check top I see that the process eats 50 GB of virtual memory and only less than 1 MB of resident memory. Is there a way to create a memory eater that really does consume it?
System specifications: Linux kernel 3.16 (Debian) most likely with overcommit enabled (not sure how to check it out) with no swap and virtualized.
Source: (StackOverflow)
I have a server with 12G of memory. A fragment of top is shown below:
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
12979 frank 20 0 206m 21m 12m S 11 0.2 26667:24 krfb
13 root 15 -5 0 0 0 S 1 0.0 36:25.04 ksoftirqd/3
59 root 15 -5 0 0 0 S 0 0.0 4:53.00 ata/2
2155 root 20 0 662m 37m 8364 S 0 0.3 338:10.25 Xorg
4560 frank 20 0 8672 1300 852 R 0 0.0 0:00.03 top
12981 frank 20 0 987m 27m 15m S 0 0.2 45:10.82 amarok
24908 frank 20 0 16648 708 548 S 0 0.0 2:08.84 wrapper
1 root 20 0 8072 608 572 S 0 0.0 0:47.36 init
2 root 15 -5 0 0 0 S 0 0.0 0:00.00 kthreadd
The free -m shows the following:
total used free shared buffers cached
Mem: 12038 11676 362 0 599 9745
-/+ buffers/cache: 1331 10706
Swap: 2204 257 1946
As I understand correctly the system has only 362 MB of available memory. So the question is how can I find out which process is consuming most of the memory?
Just for info, the system is running 64bit OpenSuse 12.
Source: (StackOverflow)