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Search found 341 results on 14 pages for 'atomic'.

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  • Are memory barriers necessary for atomic reference counting shared immutable data?

    - by Dietrich Epp
    I have some immutable data structures that I would like to manage using reference counts, sharing them across threads on an SMP system. Here's what the release code looks like: void avocado_release(struct avocado *p) { if (atomic_dec(p->refcount) == 0) { free(p->pit); free(p->juicy_innards); free(p); } } Does atomic_dec need a memory barrier in it? If so, what kind of memory barrier? Additional notes: The application must run on PowerPC and x86, so any processor-specific information is welcomed. I already know about the GCC atomic builtins. As for immutability, the refcount is the only field that changes over the duration of the object.

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  • Is Updating double operation atomic

    - by Yan Cheng CHEOK
    In Java, updating double and long variable may not be atomic, as double/long are being treated as two separate 32 bits variables. http://java.sun.com/docs/books/jls/second_edition/html/memory.doc.html#28733 In C++, if I am using 32 bit Intel Processor + Microsoft Visual C++ compiler, is updating double (8 byte) operation atomic? I cannot find much specification mention on this behavior. When I say "atomic variable", here is what I mean : Thread A trying to write 1 to variable x. Thread B trying to write 2 to variable x. We shall get value 1 or 2 out from variable x, but not an undefined value.

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  • [C++][OpenMP] Proper use of "atomic directive" to lock STL container

    - by conradlee
    I have a large number of sets of integers, which I have, in turn, put into a vector of pointers. I need to be able to update these sets of integers in parallel without causing a race condition. More specifically. I am using OpenMP's "parallel for" construct. For dealing with shared resources, OpenMP offers a handy "atomic directive," which allows one to avoid a race condition on a specific piece of memory without using locks. It would be convenient if I could use the "atomic directive" to prevent simultaneous updating to my integer sets, however, I'm not sure whether this is possible. Basically, I want to know whether the following code could lead to a race condition vector< set<int>* > membershipDirectory(numSets, new set<int>); #pragma omp for schedule(guided,expandChunksize) for(int i=0; i<100; i++) { set<int>* sp = membershipDirectory[5]; #pragma omp atomic sp->insert(45); } (Apologies for any syntax errors in the code---I hope you get the point) I have seen a similar example of this for incrementing an integer, but I'm not sure whether it works when working with a pointer to a container as in my case.

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  • Java assignment issues - Is this atomic?

    - by Bob
    Hi, I've got some questions about Java's assigment. Strings I've got a class: public class Test { private String s; public synchronized void setS(String str){ s = s + " - " + str; } public String getS(){ return s; } } I'm using "synchronized" in my setter, and avoiding it in my getter, because in my app, there are a tons of data gettings, and very few settings. Settings must be synchronized to avoid inconsistency. My question is: is getting and setting a variable atomic? I mean, in a multithreaded environment, Thread1 is about to set variable s, while Thread2 is about to get "s". Is there any way the getter method could get something different than the s's old value or the s's new value (suppose we've got only two threads)? In my app it is not a problem to get the new value, and it is not a problem to get the old one. But could I get something else? What about HashMap's getting and putting? considering this: public class Test { private Map<Integer, String> map = Collections.synchronizedMap(new HashMap<Integer, String>()); public synchronized void setMapElement(Integer key, String value){ map.put(key, value); } public String getValue(Integer key){ return map.get(key); } } Is putting and getting atomic? How does HashMap handle putting an element into it? Does it first remove the old value and put the now one? Could I get other than the old value or the new value? Thanks in advance!

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  • Making Active Directory changes atomic

    - by Matt Simmons
    I've got a Windows 2003 Active Directory infrastructure, and there are times (such as when terminating an employee) that I want instantaneous propagation across both of my AD servers. Currently, I make the change in both places, which I suspect is unhealthy, but it's the only way I know to make sure that the account is disabled to every machine. Is there a better way? Do I have to wait for the normal propagation time for convergence, or is there a way to "force" it?

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  • Is SPLFileObject atomic?

    - by Jakub Lédl
    I'm wondering whether methods of PHPs SPLFileObject are atomic (e.g. thread-safe) or not? If they aren't, I'll implement my own class, which will use flock(), but is this enough? Is the flock function really thread-safe? What if the collision occurs after I fopen() the file, but before I flock() it?

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  • [C#] Is variable assignment and reading atomic operation (threading)

    - by AStrangerGuy
    I was unable to find any reference to this in the documentations... Is assigning to a double (or any other simple type, including boolean) an atomic operation viewed from the perspective of threads? double value = 0; public void First() { while(true) { value = (new Random()).NextDouble(); } } public void Second() { while(true) { Console.WriteLine(value); } } In this code sample, first method is called in one thread, and the second in another. Can the second method get a messed up value if it gets its execution during assignment to the variable in another thread? I don't care if I recieve the old value, it's only important to receive a valid value (not one where 2 out of 8 bytes are set). I know it's a stupid question, but I want to be sure, cause I don't know how CLR actually sets the variables. Thanks

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  • Atomic INSERT/SELECT in HSQLDB

    - by PartlyCloudy
    Hello, I have the following hsqldb table, in which I map UUIDs to auto incremented IDs: SHORT_ID (BIG INT, PK, auto incremented) | UUID (VARCHAR, unique) Create command: CREATE TABLE table (SHORT_ID BIGINT GENERATED BY DEFAULT AS IDENTITY PRIMARY KEY, UUID VARCHAR(36) UNIQUE) In order to add new pairs concurrently, I want to use the atomic MERGE INTO statement. So my (prepared) statement looks like this: MERGE INTO table USING (VALUES(CAST(? AS VARCHAR(36)))) AS v(x) ON ID_MAP.UUID = v.x WHEN NOT MATCHED THEN INSERT VALUES v.x When I execute the statement (setting the placeholder correctly), I always get a Caused by: org.hsqldb.HsqlException: row column count mismatch Could you please give me a hint, what is going wrong here? Thanks in advance.

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  • How to move an element in a sorted list and keep the CouchDb write "atomic"

    - by karlthorwald
    I have elements of a list in couchdb documents. Let's say these are 3 elements in 3 documents: { "id" : "783587346", "type" : "aList", "content" : "joey", "sort" : 100.0 } { "id" : "358734ff6", "type" : "aList", "content" : "jill", "sort" : 110.0 } { "id" : "abf587346", "type" : "aList", "content" : "jack", "sort" : 120.0 } A view retrieves all "aList" documents and displays them sorted by "sort". Now I want to move the elements, when I want to move "jack" to the middle, I could do this atomic in one write and change it's sort key to 105.0. The view now returns the documents in the new sort order. After a lot of sorting I could end up with sort keys like 50.99999 and 50.99998 after some years and in extreme situations run out of digits? What can you recommend, is there a better way to do this? I'd rather keep the elements in seperate documents. Different users might edit different elements in parallel (which also can get tricky). Maybe there is a much better way?

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  • JPA atomic query/save for multithreaded app

    - by TofuBeer
    I am in the midst of changing my JPA code around to make use of threads. I have a separate entity manager and transaction for each thread. What I used to have (for the single threaded environment) was code like: // get object from the entity manager X x = getObjectX(jpaQuery); if(x == null) { x = new X(); x.setVariable(foo); entityManager.persist(x); } With that code in the multi threaded environment I am getting duplicate keys since, I assume, getObjectX returns null for a thread, then that thread is swapped out, the next thread calls getObjextX, also getting null, and then both threads will create and persist a new X(). Short of adding in synchronization, is there an atomic way to get/save-if-doesn't-exist a value with JPA or should I rethink my approach EDIT: I am using the latest Eclipselink and MySql 5.1

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  • Atomic int writes on file

    - by Waneck
    Hello! I'm writing an application that will have to be able to handle many concurrent accesses to it, either by threads as by processes. So no mutex'es or locks should be applied to this. To make the use of locks go down to a minimum, I'm designing for the file to be "append-only", so all data is first appended to disk, and then the address pointing to the info it has updated, is changed to refer to the new one. So I will need to implement a small lock system only to change this one int so it refers to the new address. How is the best way to do it? I was thinking about maybe putting a flag before the address, that when it's set, the readers will use a spin lock until it's released. But I'm afraid that it isn't at all atomic, is it? e.g. a reader reads the flag, and it is unset on the same time, a writer writes the flag and changes the value of the int the reader may read an inconsistent value! I'm looking for locking techniques but all I find is either for thread locking techniques, or to lock an entire file, not fields. Is it not possible to do this? How do append-only databases handle this? Thanks! Cauê

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  • google app engine atomic section???

    - by bokertov
    hi, Say you retrieve a set of records from the datastore (something like: select * from MyClass where reserved='false'). how do i ensure that another user doesn't set the reserved is still false? I've looked in the Transaction documentation and got shocked from google's solution which is to catch the exception and retry in a loop. Any solution that I'm missing - it's hard to believe that there's no way to have an atomic operation in this environment. (btw - i could use 'syncronize' inside the servlet but i think it's not valid as there's no way to ensure that there's only one instance of the servlet object, isn't it? same applies to static variable solution) Any idea on how to solve??? (here's the google solution: http://code.google.com/appengine/docs/java/datastore/transactions.html#Entity_Groups look at: Key k = KeyFactory.createKey("Employee", "k12345"); Employee e = pm.getObjectById(Employee.class, k); e.counter += 1; pm.makePersistent(e); This requires a transaction because the value may be updated by another user after this code fetches the object, but before it saves the modified object. Without a transaction, the user's request will use the value of counter prior to the other user's update, and the save will overwrite the new value. With a transaction, the application is told about the other user's update. If the entity is updated during the transaction, then the transaction fails with an exception. The application can repeat the transaction to use the new data. THANKS!

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  • Cannot select a node here: the context item is an atomic value

    - by user348810
    While i execute this code it shownt the following error Cannot select a node here: the context item is an atomic value,so that i can't sum up the fundunits what is the problem ? why i can't able to sum up <xsl:variable name="VAR_FUNDNAME" select="distinct-values(/SJPDATA/WEALTHSTAT[DOCUMENTTYPE=$MYDCTTYPE]/CLIENTINFO[CLIENTID=$MYCLIENT]/ancestor::*/PORTFOLIO/PENSIONS[CLIENTREF=$MYCLIENTTYPE][GROUPING=$MYGROUPINGVALUE]/PENSIONBREAKDOWN/FUNDNAME)"/> <xsl:for-each select="$VAR_FUNDNAME"> <xsl:variable name="VAR_CURFUNDNAME" select="."/> <myvar><xsl:value-of select="$VAR_CURFUNDNAME"/></myvar> <xsl:if test="(/SJPDATA/WEALTHSTAT[DOCUMENTTYPE=$MYDCTTYPE]/CLIENTINFOCLIENTID=$MYCLIENT]/ancestor::*/PORTFOLIO/PENSIONS[CLIENTREF=$MYCLIENTTYPE][GROUPING=$MYGROUPINGVALUE]/PENSIONBREAKDOWN[FUNDNAME=string($VAR_CURFUNDNAME)][UNITTYPE='Acc'])"/> <ASSETVALUATIONDATE><xsl:value-of select="min(/SJPDATA/WEALTHSTAT[DOCUMENTTYPE=$MYDCTTYPE]/CLIENTINFO[CLIENTID=$MYCLIENT]/ancestor::*/PORTFOLIO/PENSIONS[CLIENTREF=$MYCLIENTTYPE][GROUPING=$MYGROUPINGVALUE]/PENSIONBREAKDOWN[FUNDNAME=string($VAR_CURFUNDNAME)][UNITTYPE='Acc']/string(ASSETVALUATIONDATE))"/></ASSETVALUATIONDATE> <PLANNUMBER></PLANNUMBER> <FUNDNAME><xsl:value-of select="$VAR_CURFUNDNAME"/></FUNDNAME> <FUNDUNITS><xsl:value-of select="string(sum(/SJPDATA/WEALTHSTAT[DOCUMENTTYPE=$MYDCTTYPE]/CLIENTINFO[CLIENTID=$MYCLIENT]/ancestor::*/PORTFOLIO/PENSIONS[CLIENTREF=$MYCLIENTTYPE][GROUPING=$MYGROUPINGVALUE]/PENSIONBREAKDOWN[FUNDNAME=string($VAR_CURFUNDNAME)][UNITTYPE='Acc']/FUNDUNITS))"/></FUNDUNITS> </xsl:for-each>

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  • How to write a spinlock without using CAS

    - by Martin
    Following on from a discussion which got going in the comments of this question. How would one go about writing a Spinlock without CAS operations? As the other question states: The memory ordering model is such that writes will be atomic (if two concurrent threads write a memory location at the same time, the result will be one or the other). The platform will not support atomic compare-and-set operations.

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  • atomic writes to ehcache

    - by Jacques René Mesrine
    Context I am storing a java.util.List inside ehcache. Key(String) --> List<UserDetail> The ordered List contains a Top 10 ranking of my most active users. Problem Concurrent 3rd party clients might be requesting for this list. I have a requirement to be as current as possible with regards to the ranking. Thus if the ranking is changed due the activities of users, the ordered List in the cache must not be left stale for very long. Once I've recalculated a new List, I want to replace the one in cache immediately. Consider a busy scenario whereby multiple concurrent clients are requesting for the ranking; how can I replace the cache item in an fashion such that: Clients can continue to pull a possibly stale snapshot. They should never get a null value. There will only be 1 server thread that writes to the cache.

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  • How atomic *should* I make an Ajax form?

    - by b. e. hollenbeck
    I have some web forms that I'm bringing over with AJAX, and as I was dealing with the database on the back end, I thought that it might be easier to just handle each input on the form atomically with AJAX, saving the form in 'real time' as the user edits it. The forms are ~20 fields of administrative settings. Would this create massive overhead with the app, cause it to be error-prone, or is this a feasible idea? Of course, contingent operations (like a checkbox that then requires a text entry) would be held until the textbox gained and lost focus. Comments?

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  • Are batch mutations atomic in Cassandra?

    - by user317459
    The Cassandra API supports batch mutations: batch_mutate(keyspace, mutation_map, consistency_level): Executes the specified mutations on the keyspace. mutation_map is a map; the outer map maps the key to the inner map, which maps the column family to the Mutation; can be read as: map. To be more specific, the outer map key is a row key, the inner map key is the column family name. A Mutation specifies either columns to insert or columns to delete. See Mutation and Deletion above for more details. Are all mutations that are executed in a batch executed atomically? So if one of the mutations fails, do the others fail too?

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  • Are C++ Reads and Writes of an int atomic

    - by theschmitzer
    I have two threads, one updating an int and one reading it. This value is a statistic where the order of the read and write is irrelevant. My question is, do I need to synchronize access to this multi-byte value anyway? Or, put another way, can part of the write be complete and get interrupted, and then the read happen. For example, think of value = ox0000FFFF increment value to 0x00010000 Is there a time where the value looks like 0x0001FFFF that I should be worried about? Certainly the larger the type, the more possible something like this is I've always synchronized these types of accesses, but was curious what the community thought.

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  • Are Triggers Based On Queries Atomic?

    - by David
    I have a table that has a Sequence number. This sequence number will change and referencing the auto number will not work. I fear that the values of the trigger will collide. If two transactions read at the same time. I have ran simulated tests on 3 connections @ ~1 million records each and no collisions. CREATE TABLE `aut` ( `au_id` int(10) NOT NULL AUTO_INCREMENT, `au_control` int(10) DEFAULT NULL, `au_name` varchar(50) DEFAULT NULL, `did` int(10) DEFAULT NULL, PRIMARY KEY (`au_id`), KEY `Did` (`did`) ) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=latin1 TRIGGER `binc_control` BEFORE INSERT ON `aut` FOR EACH ROW BEGIN SET NEW.AU_CONTROL = (SELECT COUNT(*)+1 FROM aut WHERE did = NEW.did); END;

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  • iPhone file corruption

    - by sfider
    Is it possible (on iPhone/iPod Touch) for a file written like this: if (FILE* file = fopen(filename, "wb")) { fwrite(buf, buf_size, 1, file); fclose(file); } to get corrupted, e.g. when app is forced to terminate? From what I know fwrite should be an atomic operation, so when I write whole file with one instruction no corruption should occure. I could not find any information on the net that would say otherwise.

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