synchronization

问题 I just came across the following paragraph in the AppEngine documentation for Query Cursors: An interesting application of cursors is to monitor entities for unseen changes. If the app sets a timestamp property with the current date and time every time an entity changes, the app can use a query sorted by the timestamp property, ascending, with a Datastore cursor to check when entities are moved to the end of the result list. If an entity's timestamp is updated, the query with the cursor

问题 In a recent answer I suggested that it is possible to achieve the functionality of volatile by synchronizing on the object containing the variable we need to be volatile (asker does not have access to the variable in code). This got me thinking that I actually don't need to block on the containing object, I just need to achieve a memory barrier. As synchronized achieves both synchronisation and a memory barrier, if all I need is the memory barrier (as in this case) would it actually be better

问题 Is it possible to synchronize OpenCL work-groups? For example, I have 100 work-groups every work-groups have only one item (don't ask me why, this is an example), and I need to put barrier to every work-item which ensure that all work-groups will be continue after every work-item in this 100 work-groups reaches this barrier point. 回答1: No, you can't. You can synchronize threads inside a group, and you can synchronize kernel executions inside a command queue. You may be able to synchronize a

问题 If I have several mutable properties in an object that will be acted upon by several threads, I understand they should be synchronized. class Doggie { private String name; private int age; public void setName(String name) { this.name = name; } public String getName() { return this.name; } public void setAge(int age) { this.age = age; } public int getAge() { return this.age; } } Questions: Are not return and assignment atomic operations in Java? Since properties might not necessarily be

问题 SQL Gurus -- Our architecture consists of multiple customer databases to a common codebase. When we deploy database changes, the scripts must be run agianst each database. Because of deployment issues, there have come times when our stored procedures became out of sync with one another. I would like to create a script to return these mimatched procedures to ensure that we have sync'd copies of our databases after deployment. Is it possible to compare two or more databases, by having a script

问题 I do some scientific computations in C++, and try to utilize OpenMP for the parallelisation of some of the loops. This worked well so far, e.g. on a Intel i7-4770 with 8 threads. Setup We have a small workstation which consists of two Intel CPUs (E5-2680v2) on one mainboard. The code works as long as it runs on 1 CPU with as many threads as I like. But as soon as I employ the second CPU, I observe incorrect results from time to time (around every 50th-100th time I run the code). This happens

问题 Let's assume I declared two maps and want to assign it in two different goroutines in error group. I don't perform any reads/write. Should I protect assign operation with lock or I can omit it? UPD3: In the Java Concurrency In Practice Brian Goetz's Part I Chapter 3 Shared Objects , mentioned: Locking is not just about mutual exclusion; it is also memory visibility. To ensure that all threads see the most up-to-date values of shared mutable variables, the reading and writing threads must

问题 I am using VB.Net and would like to use a LinkedList. Only problem is that it is a multithreaded application. I saw from MSDN that Syncroot is an explicit implementation of the ICollection Interface. I found people wanting to do similar things with List(Of T). It seems that the solution there is to cast the list to the interface. I have tried to do what I would imagine to be a similar thing in VB.Net, basically: Dim TestLinkedList = New LinkedList(Of Long) SyncLock (Ctype(TestLinkedList,

问题 In my ios app, I used WKWebview.evaluateJavaScript() to execute javascript to get a div boundingRect. In my webpage, I used anjularjs to render part of my page, the page contents is as, <body ng-app="home" ng-controller="HomeController" style="min-height:700px;"> <printerinfo></printerinfo> </body> <div id="movie" style="border: 1px grey dotted; width: 120px; height: 90px;"></div> swift func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) { self.wk.evaluateJavaScript("var

问题 Closed. This question is off-topic. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed 4 years ago . I'm trying to make an application that uses stereo vision with 20fps with javacv/opencv. I've seen some camera sterio vision, but all are expensive. I heard already talking about the Minoru 3D? Anyone know if it works with javacv? Does anyone have any idea what kind of is camera used for products like this? 回答1: