Java Uuid Thread Safe

MappingManager is thread-safe and can be safely shared throughout your application. TimeZone class. Pending writes to Honeycomb will be flushed automatically when the JVM shuts down. JournalDev is one of the most popular websites for Java, Python, Android, and related technical articles. If you get back a String from the database, you would have to use to get a java date. 2, because I downloaded the Thread Safe Version and it offers to setup Apache automatically, including the needed dlls. I am not too concerned of the possiblity of duplicate ids (the chance is pretty low based on what I read from other sources). Simple Encoding and Decoding: It uses the Base64 alphabet specified by Java in RFC 4648 and RFC 2045 for encoding and decoding operations. Notez que toutes les méthodes des classes "BluetoothServerSocket" et "BluetoothSocket" sont "thread-safe". ThreadLocal there). IOException, PathNotFoundException, RepositoryException Serializes the node (and if noRecurse is false , the whole subgraph) at absPath as an XML stream and outputs it to the supplied OutputStream. locks Interfaces and classes providing a framework for locking and waiting for conditions that is distinct from built-in synchronization and monitors. By definition, static means only one instance. Here is my code:. Delete nodes from a Tree in Java; Find the root node of a tree from any node in the Java Tree; Java Tree implementation; Utilities. 0 doesn't support Apache 2. RethinkDB connection objects are not thread-safe, and calls to connect from multiple threads may change the global connection object used by repl. Annotations in Java 8 are repeatable. Join GitHub today. The synchronizedSet() method is used to return a synchronized (thread-safe) sorted set backed by the specified sorted set. From the mapper, you can then obtain a DAO instance and execute queries: id` for method findById(java. Thread Safety¶ The logging module is intended to be thread-safe without any special work needing to be done by its clients. nextBytes , which is used by the UUID. Simple Encoding and Decoding: It uses the Base64 alphabet specified by Java in RFC 4648 and RFC 2045 for encoding and decoding operations. Pending writes to Honeycomb will be flushed automatically when the JVM shuts down. java) is included in the DevDaily. AtomicLong type, so that it is thread-safe. UUID: A UUID is a 256-bit identifier that, if it is generated, is statistically guaranteed to be unique. class); User user = userAccessor. A UUID (or GUID) is a unique identifier that can be created whithout a central authority. create transaction 2. Chunk updates are not multi-thread safe; the caller must do correct synchronization. 0, Windows 95, DCOM release, and Windows 98, UuidCreate returns RPC_S_UUID_LOCAL_ONLY when the originating computer does not have an ethernet/token ring (IEEE 802. The code under test remains 100% production as the driver takes care of the redirection. 2019-07-20 00:46:27. Following is the declaration for java. From the mapper, you can then obtain a DAO instance and execute queries: id` for method findById(java. Java - Ways to Generate Unique Ids in Java. Executors is used for thread management. This library extends the standard Java UUID class to provide true v1 (time based) and v3/v5 (namespace based) identifier generation. JavaUuidGenerator —implements an ID based on the java. Like IIS's ISAPI, NetPlanet's NSAPI, Apache's module (in windows), etc. The underlying implementation uses the java. The Thread Context Map is the equivalent of the MDC and the Thread Context Stack is the equivalent of the NDC. randomUUID() Method - The randomUUID() method is used to retrieve a type 4 (pseudo randomly generated) UUID. Unlike ArrayBlockingQueue, DelayQueue is an unbounded collection. While using the Thread API in Java is simple, writing thread-safe classes is not. It would be great to avoid it. Joiner and Splitter helper classes configuration methods will always return a new instance. Android蓝牙开发 蓝牙开发 学习之前先了解两个基本概念: 1. BW engine runs into its own JVM without any Tomcat or J2EE container. Maps store a collection of pairs and operate them as a whole. The point of a UUID is that it's big enough that you can select any random ID and it doesn't clash with any other ID. 0_01/jre\ gtint :tL;tH=f %Jn! [email protected]@ Wrote%dof%d if($compAFM){ -ktkeyboardtype =zL" filesystem-list \renewcommand{\theequation}{\#} L;==_1 =JU* L9cHf lp. Nil UUID The nil UUID is special form of UUID that is specified to have all 128 bits set to zero. After allocation of the index, we can set the value of this index, specific for each thread. Instead you use Vert. pl Quarkus is the Opposite of Wildfly--airhacks. As per normal the specification was a bit thin to say the least but it gave me a chance to research what some well informed individuals where doing to help me build a singleton class that was small, fast and had a low memory. Download rubygem-thread_safe-doc-0. Spring Data MongoDB stores the type information as the last field for the actual root class as well as for the nested type (because it is complex and a subtype of Contact). fm podcast JAX-RS Client / Jersey: HTTP Tracing J4K, Quarkus, ThinWAR Startup, EJB, CDI, JavaMail--or 65th airhacks. public static Map kingdomList = new ConcurrentSkipListMap. init versus multiple calls to Cipher. I am learning a ExecutorService and try to stop execution of any thread based of custom condition. 我提出这个问题,因为有以下观察>在高度多线程环境中的线程转储中获取此堆栈跟踪 'http-80-200' daemon prio=10 tid=0x00002aaab4981000 nid=0x7520 waiting \ for monitor entry [0x000000004fec7000] java. So, if you're using such SDK configuration in a multithreaded code, which, on POSIX, you likely are, then:. While the collections are thread-safe, should a thread be preempted, you can end up with different values of belongsTo stored alongside each other. This implementation is thread safe and very fast. MappingManager manager = new MappingManager (session);. Parameters. An interface can contain any number of methods. This class must appear immutable to clients, even if it does all kinds of caching and pooling under the covers. Date and SimpleDateFormatter) aren’t thread-safe, leading to potential concurrency issues for users—not something the average developer would expect to deal with when writing date-handling code. operates with files). Applications should specify connections explicitly. Does your code use Java Reflection to execute other code? The whole MDR is thread safe. Very interesting. The world and the coords are defined into a config. 2019-07-20 00:46:27. Declaration. Note, that you cannot use your own objects, you have to use what is generated. I'm not familiar with Spark. The UUID generator is also designed to be be thread-safe without locking. util or java. Object 객체가 복사(copy)되거나 대입(assign)될 때 id도 똑같이 덮어씌워지지 않도록 주의해야 합니다. UUID, while supposedly immutable, is not thread-safe, due errors in caching the variant and hashCode. The Version 4 UUIDs produced by this site were generated using a secure random number generator. This implementation is thread safe and very fast. One small caveat - you will inevitably get messages reordered. The cuid library for ColdFusion is thread safe and uses Java's AtomicInteger class (java. # SOME DESCRIPTIVE TITLE # Copyright (C) YEAR Free Software Foundation, Inc. A UUID (or GUID) is a unique identifier that can be created whithout a central authority. What is it? clj-uuid is a Clojure library for generation and utilization of UUIDs (Universally Unique Identifiers) as described by RFC-4122. This is the case when java. Convert an int to a String in java; Tree. So does that mean that we cannot modify anything at all involving bukkit within an asynchronous thread including packets, blocks, players, and such?. What is a block of code I can use that meets my requirements? My guess is it's a requirement that the thread that calls into my API must not only get a reference to the XmlResults, but also to the transaction, and actually commit the transaction when done with results?. UUID is immutable so it's potentially thread safe, but apparently there was some evil caching going on in some accessors that made it unsafe (that bug is fixed now). As soon as there is more than one user, or concurrent useage of the axis2 engine, the soap messages for the request/responses are not alligned properly causing the system to become unusable. randomUUID de Java? ¿Cómo puedo obtener el UUID de mi teléfono Android en una aplicación? ¿Generando un UUID en Postgres para la instrucción Insertar? ¿Cuándo está realmente obligado a usar UUID como parte del diseño? Cómo leer un. Generate Unique id using UUID in java - Program Talk. UUID import org. Java does not guarantee that mDiscoveryListeners is non-null here. First, we define a wrapper annotation which holds an array of the actual annotations:. RxJava: Idiomatic Concurrency — flatMap() vs. This makes these classes as thread safe and can be usable as a static final constant. Twitter的分布式自增ID算法snowflake (Java版) 概述 分布式系统中,有一些需要使用全局唯一ID的场景,这种时候为了防止ID冲突可以使用36位的UUID,但是UUID有一些缺点,首先他相对比较长,另外UUID一般是无序的。. Additionally, a number of useful supporting utilities are provided. Sto lavorando su un database distribuito. Agents are thread-safe; all modifications are sequenced and applied in order, one after another. This component would then be instantiated and used in exactly the same way the non-thread safe version would be used:. We're giving away four copies of Java 13 Revealed: For Early Adoption and Migration and have Kishori Sharan on-line! See this thread for details. This is why there are things such as CopyOnWriteArrayList and locked queues. See the code for self-explanatory. If you can't control access to a call that isn't thread safe, then you can't call it safely at all if there's any code in your process that you don't control (like, say, third-party libraries, or even first-party libraries). WrapperConcurrentMap. I mean your engine needs to be thread safe so it's a good idea to use a command queue for that. An interface implementation may be added to any existing third party class. This Java tutorial is to learn about the collection LinkedBlockingQueue which is an implementation of Java BlockingQueue. While I was developing a plugin, I needed to teleport a player to a specific location which is in another world. Well, I have a question: In order to manage multiple mini-games in my server I have made the Arena class a abstract one, and any Arenas just inherit it (Exemple: ArenaSkyWars extends Arena, OR ArenaMurder extends Arena) and I just have as many objects of that subclass needed. 2) Is there some site that has the algorithm(s) documented? 3) Are GUIDs guaranteed unique - rumors are that PCs without a network card could POSSIBLY generate the same ids. 5/0000777000212300001630000000000010557451004006637 5swish-e-2. First, we define a wrapper annotation which holds an array of the actual annotations:. The UUID is intended to be used as a unique identifier of a particular recommendation served to a user, so that response rates to recommendations can be measured. class); User user = userAccessor. A small toolkit of classes that support lock-free thread-safe programming on single variables. Thread safety: This class is thread safe and may be shared between multiple processing threads, except for the #registerCustomType and #registerCustomTypes methods. In Java, we often use primitive datatypes like short, int, long, float, double, boolean etc. In JDK 5 they provided similar class called StringBuilder in Java which is a copy of StringBuffer but without synchronization. UUID usa java. The methods of this class are for manipulating the Leach-Salz variant, although the constructors allow the creation of any variant. RFC 4122 describes a method for generating GUIDs which should be fairly close to what Windows actually does. Generate Unique id using UUID in java; Delete by id in hibernate; Download an Excel using Servlet; Thread safe caching of JAX-WS clientproxies; Run any command via Java, You can even shutdown your computer. Java 8 provides a new feature Base64 to deal with decryption and encryption. Thread Safe Best Lightweight General Purpose Java. The cookie handling is missing two important parameters:. class); User user = userAccessor. 4: > Set all the other bits to randomly (or pseudo-randomly) chosen values. Jdbi 3 is the third major release which introduces enhanced support for Java 8, countless refinements to the design and implementation, and enhanced support for modular plugins. randomUUID? Why is Java's SimpleDateFormat not thread-safe? Is Java's assertEquals method reliable? Is it good practice to use java. locks Interfaces and classes providing a framework for locking and waiting for conditions that is distinct from built-in synchronization and monitors. As it happens, Java's UUID. Final in Java is very important keyword and can be applied to class, method, and variables in Java. In an application with many of users the default Java UUID generator could take more than 2 milliseconds to generate each identifier. This is already handled by the Map/Reduce {MRTask) framework. In addition to these default mappings, you can register your own types with custom codecs. Contains the collections framework, legacy collection classes, event model, date and time facilities, internationalization, and miscellaneous utility classes (a string tokenizer, a random-number generator, and a bit array). The problem that I had before when trying to use a transaction during query is the following: 1. Implementation of UUID generator that uses time/location based generation method (variant 1). You can also have an in-ram unique number server with a thread safe access. In this quick article, we'll be looking at the ConcurrentSkipListMap class from the java. AtomicLong type, so that it is thread-safe. 4 - The process, knowlodge base, and etc it's in a remote server. toString() when used from multiple threads and there is no clear answer on the net about whether it is really thread-safe or not. Object expressions. Thread pools are used to move work that might take longer to complete away from the main application, as well as constraining how much of this work can be done in parallel with the application. Your loop is incorrect. ContextCalculator implementations must be thread safe, because they may be called from outside of the main thread, or even called in parallel. return XmlResults to caller As you know, in step 3 above, committing the transaction closes the db connection, invalidating the XmlResults object. Except, that’s not really how Java programming works these. A UUID (or GUID) is a unique identifier that can be created whithout a central authority. This class describes the usage of SocketIOServer. This article help to understand and best use of Guava's string helper classes, Joiner, Splitter, CharMatcher and Charsets. The article describes how to use the Microsoft's UPnP Control Point API for finding and controlling UPnP devices, and includes a description of simple library to facilitate the application of Control Point API in your own programs, together with an example of MFC and WinForms applications. Although, I need to check every key in an Entry, checking if it's a valid UUID or not. The point of a UUID is that it's big enough that you can select any random ID and it doesn't clash with any other ID. Can someone guide me how i can add sleep in any thread using ExecutorService. timeout 0s Used by the ShellBasedUnixGroupsMapping class, this property controls how long to wait for the underlying shell command that is run to fetch groups. It is thread-safe because the synchronized term in the method generate(), but I have the feeling that it is possible to implement this generation in a better way. currently the issue is we have a synchronized block which makes sure for each message ID, NAME and ACCOUNT a unique Uuid is Thread safety- span across multiple jvm. commit transaction 4. currently the issue is we have a synchronized block which makes sure for each message ID, NAME and ACCOUNT a unique Uuid is Thread safety- span across multiple jvm. They basically have to be thread safe, because they're globally accessible. UUIDs can be used if a sequence number is not good enough. springframework. This is because the access through a singleton can mean that the class instance can be NULL at any point in time within an asynchronous environment, see This is because the access through a singleton can mean that the class instance can be NULL at any point in time within an asynchronous environment, see. Jdbi provides convenient, idiomatic access to relational data in Java. 1 we now delegate processing to a single worker thread if the calling thread is not bound. The test thread is assigned a special UUID which is then tied to the test schemas. I am learning a ExecutorService and try to stop execution of any thread based of custom condition. UserAccessor userAccessor = manager. Thread Safety¶ The logging module is intended to be thread-safe without any special work needing to be done by its clients. JournalDev is one of the most popular websites for Java, Python, Android, and related technical articles. You can vote up the examples you like. This Java tutorial is to learn about the collection LinkedBlockingQueue which is an implementation of Java BlockingQueue. Following is the declaration for java. An interface is not extended by a class; it is implemented by a class. Another way could be to use a sequence generator from a DB, but again has the central connection. Also, read the instructions for how to report a bug that someone will want to help fix. public class NameBasedGenerator extends StringArgGenerator. 0 - update to mc 1. Any way you title it, GUIDs or UUIDs are just big, gigantic ID numbers. Join GitHub today. When you use CFThread to run code asynchronously in ColdFusion, all threads in a given request need to be uniquely named. Of course if node identifier is set in configuration then UUID would not be generated. The trigger functionality is provided by MyBatis. UUID - Universally Unique Identifier. class); User user = userAccessor. In this post, we look at Java concurrency, synchronization, and how manipulating an object from multiple threads can pose a problem when the object holds state. yes XTS is thread safe. Example code. Problem and Solution Productive Java EE, MicroProfile, AI and Deep Learning--airhacks. In case you opt for Bean managed concurrency, you as a bean developer are responsible for the thread safety of objects used within the Singleton bean e. concurrent package. My latest revision (I guess number 10 :) is thread safe and uses 'swap' which should be very efficient as compared with full blown STM. To avoid this, from version 0. StackTraceElement; Java enums (ideally they should be) java. It contains well written, well thought and well explained computer science and programming articles, quizzes and practice/competitive programming/company interview Questions. This implementation is thread safe and very fast. In Windows NT 4. 10规程的串行线性仿真协议。. Another way to do it is to use large pseudorandom numbers and count on the improbability of two numbers being picked the same. Therefore will the auto-detection mode turn XStream's marshalling process in a thread-unsafe operation. It is known that we shouldn't use the Bukkit API in asynchronous threads. uuid가 매칭이 될 때 연결이 수락된다. It generates UUIDs according to the UUID specification (RFC-4122) (also see Wikipedia UUID page for more explanation) JUG was written by Tatu Saloranta. A Version 4 UUID is a universally unique identifier that is generated using random numbers. UserAccessor userAccessor = manager. Generates an integer containing the user-specified number of pseudo-random bits (right justified, with leading zeros). It is ready to use; you do not need to build or compile it, in order to use it. # This file is distributed under the same license as the PACKAGE package. In JDK 5 they provided similar class called StringBuilder in Java which is a copy of StringBuffer but without synchronization. When Initialization Occurs A class or interface type T will be initialized immediately before the first occurrence of any one of the following:. fm podcast J4K, Quarkus. In this case, the generated UUID is a valid identifier, and is guaranteed to be unique among all UUIDs generated on the computer. However, there was a thread safety bug involving Ecore annotations, which is now fixed but will still affect older releases of EMF. java) is included in the DevDaily. This makes these classes as thread safe and can be usable as a static final constant. Although the bug is left unfixed for backward compatibility, please check your UUIDs or even better, use fromUuid(java. My latest revision (I guess number 10 :) is thread safe and uses 'swap' which should be very efficient as compared with full blown STM. > A correctly generated v4 UUID (S4. Parameters. randomUUID() (or an equivalent algorithm) or its own unique ID generator. Hi, The only "secure" way is using CATIA through CATIA Integration. [The UUID can be transfered by hitting TAB when looking at the villager during entering the command. The synchronizedSortedSet() method is used to get a synchronized (thread-safe) sorted set backed by the specified sorted set. Iterable Represents a set of elements that make up a sortable, typed key. They basically have to be thread safe, because they're globally accessible. Delete nodes from a Tree in Java; Find the root node of a tree from any node in the Java Tree; Java Tree implementation; Utilities. Spring Data MongoDB stores the type information as the last field for the actual root class as well as for the nested type (because it is complex and a subtype of Contact). Pending writes to Honeycomb will be flushed automatically when the JVM shuts down. public class NameBasedGenerator extends StringArgGenerator. Is there any thread-safe method to do this without calling the Mojang API, as I want to benefit from the caching on the server? Async Player Name to UUID without. make sure the high key is guaranteed to be larger than you'll ever need, make the key a long rather than an int, and avoid Strings. Problem and Solution Productive Java EE, MicroProfile, AI and Deep Learning--airhacks. With MyBatis, we still need the sequence. This is why there are things such as CopyOnWriteArrayList and locked queues. 如题所述,有根据最好了,或者说在highly mutilthread env环境下,加synchronized wrapper下吗,怎么才能比较好的降低并发产生,又不大范围(如果使用这个生成随机串的次数很多,比如一天百万级别的,对于生成随机串怎么降低或者说保证唯一)影响性能. This implementation is thread safe and very fast. This relation is represented as Map booksById and Map booksByAuthorTitle AuthorTitle is helper class that holds author + title and is implements equals() LibraryService is able to identify User by its id or name (putting aside for the moment that multiple users can have the same name). Agents are thread-safe; all modifications are sequenced and applied in order, one after another. Additionally, move Saving of the User cache to be done async, incase: the user never changed the default setting for Spigot's save on stop only. This Jsondata is different so we need to convert it to an JsonArray Instead JsonObject. Nil UUID The nil UUID is special form of UUID that is specified to have all 128 bits set to zero. 6 LTS with about 4600 projects (we scan a lot of branches). Impetus Codec was formed as an attempt to focus development effort on one definitive implementation of the Base64 encoder. toString(new URL(url)); Step 3. util; import java. JavaUuidGenerator —implements an ID based on the java. This functionality is only available for legacy reasons. THE unique Spring Security education if you're working with Java today. On paper you could generate a UUID per request, insert it into the MDC and presto you have a UUID per request in each log line! Since threads are created per request, the MDC will be empty each time. * But when we talk about thread safe Java methods, it's recommended that you use "Synchronized" to protect particular steps in a method for thread safety. Thread Safety¶ The logging module is intended to be thread-safe without any special work needing to be done by its clients. Therefore I would say thread-safety is a required feature of a GUID generator. If you are using FastCGI, it is better to use Non Thread-Safe to gain thus small performance improvement for not checking thread safety. UUID generates version 1 UUIDs that contain the the MAC address of a network card. In this example three threads are created and all of them share the same string object. A small toolkit of classes that support lock-free thread-safe programming on single variables. Sto cercando di generare un ID univoco che servirà come un famiglia colonna di chiave primaria in cassandra. TypeHandler UUID. package com. The UUID generator in Scala After I was done with the multi-threading test of the UUID generator, I tried to develop a Scala version, since I am learning it and specially interested in the Actors model (I think that is the major attraction to java developers). randomUUID() Method - The randomUUID() method is used to retrieve a type 4 (pseudo randomly generated) UUID. Uniqueness is supported by the millisecond precision timestamp, the MAC address of the generating machine, the 2 byte process id, and a 4 byte counter. The node value is only meaningful in a time-based UUID, which has version type 1. fm podcast J4K, Quarkus. It's obvious that this code isn't thread-safe (ArrayList isn't thread-safe, and tokens is accessed without any explicitly locking), but I don't know whether Spark provides the thread safety. If you can't control access to a call that isn't thread safe, then you can't call it safely at all if there's any code in your process that you don't control (like, say, third-party libraries, or even first-party libraries). For to this reason, all non-name or non-uuid based ContextCalculator s (such as location-based ones) have to utilize a cache and must be to be updated using event listeners or synchronized schedulers. Join GitHub today. UUID: cryptographically strong pseudo random number generator. [2009-07-09 14:58 UTC] xeckit at gmail dot com I suppose the Non Thread Safe version of PHP 5. Problem and Solution Productive Java EE, MicroProfile, AI and Deep Learning--airhacks. fm podcast JAX-RS Client / Jersey: HTTP Tracing J4K, Quarkus, ThinWAR Startup, EJB, CDI, JavaMail--or 65th airhacks. There is another email thread on this posted on March 12, 2007 which I believe is the same problem I am seeing. * Transformers are specified in dot notation just like include and exclude methods, but it doesn't * support wildcards. Android蓝牙开发 蓝牙开发 学习之前先了解两个基本概念: 1. with the name uuid and the value a random. UUID generates version 1 UUIDs that contain the the MAC address of a network card. randomUUID() returning the same UUID under high load; Jetty not thread safe under high load; HTTP 1. 1 we now delegate processing to a single worker thread if the calling thread is not bound. com/2013/08/02/12c-asynchronous-global-index-maintenance-part. In an application with many of users the default Java UUID generator could take more than 2 milliseconds to generate each identifier. The main thread waits for certain events and then assigns items to be processed to different threads. JUG versions 3. Convert an int to a String in java; Tree. ContainerProperties. Android example source code file (BluetoothSocket. Joiner and Splitter helper classes configuration methods will always return a new instance. The underlying implementation uses the java. The simplest fix is to allocate those two maps from the constructor. info For your. public class Identifier extends java. Tutorial Make a minigame plugin! import java. Winston Edit: Having looked at the API for version 7, UUID still doesn't appear to have an automated method for generating time-based UUIDs, so you'll have to create them yourself (the algorithm is described in the RFC). UUID; /** * This class is an array of integers that is backed by shared memory. 如题所述,有根据最好了,或者说在highly mutilthread env环境下,加synchronized wrapper下吗,怎么才能比较好的降低并发产生,又不大范围(如果使用这个生成随机串的次数很多,比如一天百万级别的,对于生成随机串怎么降低或者说保证唯一)影响性能. This class describes the usage of SocketIOServer. Your own UUID 2: 26. We distinguish index for TLS. When writing a custom type handler, make sure to handle null values and empty strings. Spring Data MongoDB stores the type information as the last field for the actual root class as well as for the nested type (because it is complex and a subtype of Contact). time Date/Time classes instead. This functionality is only available for legacy reasons. Problem: is my code thread-safe? Thread-safe code can handle calls from many threads at once without crashing. Serializable; import java. leiningen/core/main$resolve_and_apply. Object Expressions and Declarations. Parameters. This tutorial gives you simple way to find unique values in ArrayList using TreeSet and HashSet. Bloomberg Java API Wrapper: jBloomberg. virendersharma Tuesday, September 27, 2011. 1 we now delegate processing to a single worker thread if the calling thread is not bound. 8 - move baubles to a capabilities based system which should hopefully solve a lot of longstanding issues - compatible with older saves 1. randomUUID factory, which definitely is thread-safe. This is the case when java. Java ThreadLocal is used to create thread-local variables. Generate Unique id using UUID in java; Delete by id in hibernate; Download an Excel using Servlet; Thread safe caching of JAX-WS clientproxies. It can encapsulate an identifier that is a 16-byte UUID, or an integer. A small toolkit of classes that support lock-free thread-safe programming on single variables.