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• is there a flag "M_FAST" in FreeBSD kernel for Malloc Call ?

  - by KaluSingh Gabbar

  if you know there is one, can you let me know what its for ? if not please say so : ) thanks. Signature : void * malloc(unsigned long size, struct malloc_type type, int flags); for example. other flags are... M_ZERO Causes the allocated memory to be set to all zeros. M_WAITOK Indicates that it is OK to wait for resources. If the request cannot be immediately fulfilled, the current process is put to sleep to wait for resources to be released by other processes. The malloc(), realloc(), and reallocf() functions cannot return NULL if M_WAITOK is specified.** This is the root of my confusion EDIT: The clarification for M_FAST is made in my answer below.

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• Updating a database periodically with Java

  - by MSR

  I would like to perform updates to a MySQL database using two separate classes (that do different things) -- one doing so every 10 seconds, and the second every minute. I have a few gaps in my Java knowledge and I'm wondering what the best way to achieve it is. Importantly, if connectivity to the database is lost, I need reconnection attempts to occur indefinitely, and I'm guessing the use of Prepared Statements will make queries more efficient. Should the connection to the database be left open all the time or closed between the updates being run? Maybe I also need to think about clearing objects/resources out of memory if the class instances are going to be run indefinitely.

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• Annotation retention policy: what real benefit is there in declaring `SOURCE` or `CLASS`?

  - by watery

  I know there are three retention policies for Java annotations: CLASS: Annotations are to be recorded in the class file by the compiler but need not be retained by the VM at run time. RUNTIME: Annotations are to be recorded in the class file by the compiler and retained by the VM at run time, so they may be read reflectively. SOURCE: Annotations are to be discarded by the compiler. And although I understand their usage scenarios, I don't get why it is such an important thing to specify the retention policy that retention policies exist at all. I mean, why aren't all the annotations just kept at runtime? Do they generate so much bytecode / occupy so much memory that stripping those undeclared as RUNTIME does make that much difference?

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• Can I make a pointer to the code, and pass to the next instruction?

  - by drigoSkalWalker

  Like this link http://gcc.gnu.org/onlinedocs/gcc-3.3.1/gcc/Labels-as-Values.html I can get the memory address of an label, so if I declare a label, get your address, and add your address, i will pass to next instruction? some ilustration int main () { void *ptr; label: instruction 1; instruction 2; ptr = &&label; // So if I do it... ptr = ptr + 1; // I will get the instruction 2 correct?? Thanks for all answers.

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• What is the result of "new int[ 0 ]"? [closed]

  - by ArunSaha

  Possible Duplicates: What does zero-sized array allocation do/mean? C++ new int[0] — will it allocate memory? int * p; p = new int[ 0 ]; What is the expected outcome when new is called for zero number of elements? Is the outcome defined or undefined? Further, is it okay to call delete [] p; on that pointer? What is the intuition/analogy to this situation of pointer to an array of zero elements? Thanks in advance. Regards, Arun

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• Should filters write to the response during or after filtering?

  - by Mark

  I have a filter which processes generated HTML and rewrites certain elements. For example, it adds class attributes to some anchors. Finally, it writes the processed HTML to the response (a subclass of HttpServletResponseWrapper). Naturally, this means that the processed HTML is a different length after it has passed through the filter. I can see two ways of approaching this. One is to iterate over the HTML, using a StringBuilder to build up the processed HTML, and write the processed HTML to the response once all filtering is complete. The other is to iterate over the HTML but to write it to the response as soon as each element has been processed. Which is the better way for this operation, or is there another option which would be preferable? I am looking to minimise temporary memory usage primarily.

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• Does a servlet-based stack have significant overheads?

  - by John

  I don't know if it's simply because page-loads take a little time, or the way servlets have an abstraction framework above the 'bare metal' of HTTP, or just because of the "Enterprise" in Jave-EE, but in my head I have the notion that a servlet-based app is inherently adding overhead compared to a Java app which simply deals with sockets directly. Forget web-pages, imagine instead a Java server app where you send it a question over an HTTP request and it looks up an answer from memory and returns the answer in the response. You can easily write a Java socket-based app which does this, you can also do a servlet approach and get away from the "bare metal" of sockets. Is there any measurable performance impact to be expected implementing the same approach using Servlets rather than a custom socket-based HTTP listening app? And yes, I am hazy on the exact data sent in HTTP requests and I know it's a vague question. It's really about whether servlet implementations have lots of layers of indirection or anything else that would add up to a significant overhead per call, where by significant I mean maybe an additional 0.1s or more.

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• Volatile keyword

  - by Tiyoal

  Say I have two threads and an object. One thread assigns the object: public void assign(MyObject o) { myObject = o; } Another thread uses the object: public void use() { myObject.use(); } Does the variable myObject have to be declared as volatile? I am trying to understand when to use volatile and when not, and this is puzzling me. Is it possible that the second thread keeps a reference to an old object in its local memory cache? If not, why not? Thanks a lot.

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• Reason for .Net UI Element Thread-restriction

  - by Charles Bretana

  We know that it is not possible to execute code that manipulates the properties of any UI element from any thread other than the thread the element was instantiated on... My question is why? I remember that when we used COM user interface elements, (in COM/VB6 days), that all UI elements were created using COM classes and co-classes that stored their resources using a memory model referred to as Thread-Local-Storage (TLS) , but as I recall, this was required because of something relaetd to the way COM components were constructed, and should not be relevant to .Net UI elements. Wha's the underlying reason why this restriction still exists? Is it because the underlying Operating System still uses COM-based Win32 API classes for all UI elements, even the ones manipulated in a managed .Net application ??

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• PHP+MYSQL Server Config

  - by Matias

  Hi guys, I am parsing an XML file with PHP and inserting the rows in a MYSQL database. I am using PHP simplexml_load_files to load the XML and a foreach to loop through the array and insert the rows into my database. It works perfectly fine with small files i am testing, but it comes to reality I need to parse a large 500mb XML file and nothing happens. I was wondering what was the right Php.ini config for this case ? I have a VPS Linux Cent OS, with 256 mb of dedicated Memory and MYSQL 5.0.5. I have also set php memory_limit = 256M (maximum of my server) Any suggestions, similar experiences will be greatly appreciated Thanks

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• how to save image and data locally in iphone device

  - by MaheshBabu

  Hi folks, I am getting image and some details from .net web server. I need to store these details in iphone device memory(not in sdcard),Because I need to connect web services only one time,that is at installing my app. From Next time onwards i need to get data from device. I have some knowledge in java,In java i use files to store image and Hash table to store details. How can i done this in iphone. can any one pls help me. Thank u in advance.

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• Android app crashes on second run

  - by Nick

  I have been working on my app and it runs on the simulator fine. I loaded it into my phone and now I have a problem. It runs fine when I first start it and also if I pick home and then restart it; however, if I use the back arrow and then restart it it crashes on that time, but will work out the next time I start it. I think it has to do with some kind of memory build up, but I verified onDestroy is being called, I figured that deletes everything my program created, right?

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• I want to make my own Malloc

  - by Unknown

  I want to make my own malloc/free so I can make a precise copying allocator. Any gurus have any tips and suggestions? I have a few questions for now: Should I just malloc large chunks of memory, and then distribute from that so I don't have to call the system calls? How are copying collectors usually done? I would imagine that this part is a bit complicated to do efficiently. My naive implementation would just malloc a block the size of the remaining objects which would require 2x the space.

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• What happens if an asynchronous delegate call never returns?

  - by RichardHowells

  I found a decent looking example of how to call a delegate asynchronously with a timeout... http://www.eggheadcafe.com/tutorials/aspnet/847c94bf-4b8d-4a66-9ae5-5b61f049019f/basics-make-any-method-c.aspx. In summary it uses WaitOne with a timeout to determine if the call does not return before the timeout expires. I also know that you should have an EndInvoke to match each BeginInvoke. So what happens if the wait timeout expires? We (presumably) DON'T want to call EndInvoke as that will block. The code can go on to do 'other things', but have we leaked anything? Is there some poor thread someplace blocked waiting for a return that's never going to happen? Have we leaked some memory where the result-that-will-never-return was going to be placed?

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• Change url property of .sitemap

  - by user555209

  Hello I have multiple .sitemap xml defined with different providers. For one xml file, I want to change the url (append Customerid in the url) by taking the existing url in xml file. I want this to be changed when the page is loaded the first time. For eg one of my node is And I want to make it as I have read many articles online talking about changing node in memory but cant make it work. Any help would be appreciated. Not working with breadcrumbs or sitemapPath control.

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• Extracting a reference from a c++ vector

  - by Archanimus

  Hello folks, I have a vector< vector< vector< int and I would like to extract from it a vector< vector< int to process it individually. The problem is that when I write : myMatrix = myCube[anIndex]; the matrix is copied but I only want a reference in order to save memory. Can you please help me out ? Thanks a lot!

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• Efficient questions

  - by rayman

  Hi, I have to manage xml's and Strings in my app. by efficenty and memory saving, is collection(ArrayList) will be much more 'expensive' then array of Strings? another issue is: i could use the content as regular String, or XML.. is working with XML also makes it more 'expensive' ? when i say i expensive i talk about taking system sources. please tell me by any of your exprience if the diffrences are significant? thanks, ray.

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• Reason for different segments in Linux on x86

  - by anjruu

  Hey all, So, I know that Linux uses four default segments for an x86 processor (kernel code, kernel data, user code, user data), but they all have the same base and limit (0x00000000 and 0xfffff), meaning each segment maps to the same set of linear addresses. Given this, why even have user/kernel segments? I understand why there should be separate segments for code and data (just due to how the x86 processor deals with the cs and ds registers), but why not have a single code segment and a single data segment? Memory protection is done through paging, and the user and kernel segments map to the same linear addresses anyway. Thanks! anjruu

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• C# array problem

  - by user208080

  Hi there. I am a newbie in C# and here are 2 questions: I have a 2d array a[3,3], how can I express one dimension as a new array and pass to some function. i.e. int[,] a = new int[3,3]; a[0,0] = 1; ... string b = concatenate(a[0]); // where concatenate is a function take a one dimension array as param Can I create a 65000x65000 array with C#? I got some "out of memory" error. Thanks in advance.

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• Returning the address of local or temporary variable

  - by Dave18

  #include <iostream> int& foo() { int i = 6; std::cout << &i << std::endl; return i; } int main() { int i = foo(); std::cout << &i << std::endl; } I know it doesn't return the address of local variable so that is why the warning but why does it still works and assign the variable i in main() to '6'? How does it only return the value if the variable the was removed from stack memory?

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• Using temporary arrays to cut down on code - inefficient?

  - by tommaisey

  I'm new to c++ (and SO) so sorry if this is obvious. I've started using temporary arrays in my code to cut down on repetition and to make it easier to do the same thing to multiple objects. So instead of: MyObject obj1, obj2, obj3, obj4; obj1.doSomming(arg); obj2.doSomming(arg); obj3.doSomming(arg); obj4.doSomming(arg); I'm doing: MyObject obj1, obj2, obj3, obj4; MyObject* objs[] = {&obj1, &obj2, &obj3, &obj4}; for (int i = 0; i !=4; ++i) objs[i]->doSomming(arg); Is this detrimental to performance? Like, does it cause unnecessary memory allocation? Is it good practice? Thanks.

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• Why does C++ linking use virtually no CPU? (updated)

  - by John

  On a native C++ project, linking right now can take a minute or two, yet during this time CPU drops from 100% during compilation to virtually zero. Does this mean linking is primarily a disk activity? If so, is this the main area an SSD would make big changes? But, why aren't all my OBJ files (or as many as possible) kept in RAM after compilation to avoid this? With 4Gb of RAM I should be able to save a lot of disk access and make it CPU-bound again, no? update: so the obvious follow-up is, can VC++ compiler and linker talk together better to streamline things and keep OBJ files in memory, similar to how Delphi does?

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• C# how to store those information?

  - by 5YrsLaterDBA

  I have a PrivilegeGroup table, a Privileges table and a link table because the PrivilegeGroup table and the Privileges table is a many to many relationship. I am thinking about load all contents of PrivilegeGroup table and Privilege table into memory from database at beginning when application started. I want to save them in a form easily to look up. Usually we will look up the PrivilegeCode via GroupId. Which structure is good for this purpose? array of list? dictionary?

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• PHP find if file data is an image

  - by Christian Sciberras

  Imagine I have some file data in a variable $data. I need to determine whether it is an image or not. No need for details such as corrupt images etc. Firs thought would be getting the file mime type by looking at the magic number and then see whether "image" is in the mime type. No such luck, even if I have a "file extension to mime type" script, I don't have a reliable way to get mime from magic number. My next option was to have a reasonable list of image file magic numbers and consult them. However, it relatively difficult to find such magic numbers (gif for instance has different magic numbers, some of which could pretty rare - if memory serves me right). A better idea would be some linux program which can do this kind of thing. Any ideas? I'm running RHEL and PHP 5.3. I've got root access - ie able to install stuff if needed. - Chris.

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• INSERT INTO ... SELECT ... vs dumping/loading a file in MySQL

  - by Daniel Huckstep

  What are the implications of using a INSERT INTO foo ... SELECT FROM bar JOIN baz ... style insert statement versus using the same SELECT statement to dump (bar, baz) to a file, and then insert into foo by loading the file? In my messing around, I haven't seen a huge difference. I would assume the former would use more memory, but the machine that this runs on has 8GB of RAM, and I never even see it go past half used. Are there any huge (or long term) performance implications that I'm not seeing? Advantages/disadvantages of either?

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