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Handle (computing)
In computer programming, a handle is an abstract reference to a resource that is used when application software references blocks of memory or objects that are managed by another system like a database or an operating system. A resource handle can be an opaque identifier, in which case it is often an integer number (often an array index in an array or "table" that is used to manage that type of resource), or it can be a pointer that allows access to further information. Common resource handles include file descriptors, network sockets, database connections, process identifiers (PIDs), and job IDs. PIDs and job IDs are explicitly visible integers; while file descriptors and sockets (which are often implemented as a form of file descriptor) are represented as integers, they are typically considered opaque. In traditional implementations, file descriptors are indices into a (per-process) file descriptor table, thence a (system-wide) file table. Comparison to pointers Whil ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Callback (computer Programming)
In computer programming, a callback or callback function is any reference to executable code that is passed as an argument to another piece of code; that code is expected to ''call back'' (execute) the callback function as part of its job. This execution may be immediate as in a synchronous callback, or it might happen at a later point in time as in an asynchronous callback. Programming languages support callbacks in different ways, often implementing them with subroutines, lambda expressions, blocks, or function pointers. Design There are two types of callbacks, differing in how they control data flow at runtime: ''blocking callbacks'' (also known as ''synchronous callbacks'' or just ''callbacks'') and ''deferred callbacks'' (also known as ''asynchronous callbacks''). While blocking callbacks are invoked before a function returns (as in the C example below), deferred callbacks may be invoked after a function returns. Deferred callbacks are often used in the context of I/ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Database Connection
A database connection is a facility in computer science that allows client software to talk to database server software, whether on the same machine or not. A connection is required to send commands and receive answers, usually in the form of a result set. Connections are a key concept in data-centric programming. Since some DBMS engines require considerable time to connect, connection pooling was invented to improve performance. No command can be performed against a database without an "open and available" connection to it. Connections are built by supplying an underlying driver or provider with a connection string, which is a way of addressing a specific database or server and instance as well as user authentication credentials (for example, ''Server=sql_box;Database=Common;User ID=uid;Pwd=password;''). Once a connection has been built it can be opened and closed at will, and properties (such as the command time-out length, or transaction, if one exists) can be set. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computer Security
Computer security, cybersecurity (cyber security), or information technology security (IT security) is the protection of computer systems and networks from attack by malicious actors that may result in unauthorized information disclosure, theft of, or damage to hardware, software, or data, as well as from the disruption or misdirection of the services they provide. The field has become of significance due to the expanded reliance on computer systems, the Internet, and wireless network standards such as Bluetooth and Wi-Fi, and due to the growth of smart devices, including smartphones, televisions, and the various devices that constitute the Internet of things (IoT). Cybersecurity is one of the most significant challenges of the contemporary world, due to both the complexity of information systems and the societies they support. Security is of especially high importance for systems that govern large-scale systems with far-reaching physical effects, such as power distrib ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Memory Leak
In computer science, a memory leak is a type of resource leak that occurs when a computer program incorrectly manages memory allocations in a way that memory which is no longer needed is not released. A memory leak may also happen when an object is stored in memory but cannot be accessed by the running code (i.e. unreachable memory). A memory leak has symptoms similar to a number of other problems and generally can only be diagnosed by a programmer with access to the program's source code. A related concept is the "space leak", which is when a program consumes excessive memory but does eventually release it. Because they can exhaust available system memory as an application runs, memory leaks are often the cause of or a contributing factor to software aging. Consequences A memory leak reduces the performance of the computer by reducing the amount of available memory. Eventually, in the worst case, too much of the available memory may become allocated and all or part of the syst ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Resource Leak
In computer science, a resource leak is a particular type of resource consumption by a computer program where the program does not release resources it has acquired. This condition is normally the result of a bug in a program. Typical resource leaks include memory leak and handle leak, particularly file handle leaks, though memory is often considered separately from other resources. Examples of resources available in limited numbers to the operating system include internet sockets, file handles, process table entries, and process identifiers (PIDs). Resource leaks are often a minor problem, causing at most minor slowdown and being recovered from after processes terminate. In other cases resource leaks can be a major problem, causing resource starvation and severe system slowdown or instability, crashing the leaking process, other processes, or even the system. Resource leaks often go unnoticed under light load and short runtimes, and these problems only manifest themselves under ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Software Bug
A software bug is an error, flaw or fault in the design, development, or operation of computer software that causes it to produce an incorrect or unexpected result, or to behave in unintended ways. The process of finding and correcting bugs is termed "debugging" and often uses formal techniques or tools to pinpoint bugs. Since the 1950s, some computer systems have been designed to deter, detect or auto-correct various computer bugs during operations. Bugs in software can arise from mistakes and errors made in interpreting and extracting users' requirements, planning a program's design, writing its source code, and from interaction with humans, hardware and programs, such as operating systems or libraries. A program with many, or serious, bugs is often described as ''buggy''. Bugs can trigger errors that may have ripple effects. The effects of bugs may be subtle, such as unintended text formatting, through to more obvious effects such as causing a program to crash, freezing th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Handle Leak
A handle leak is a type of software bug that occurs when a computer program asks for a handle to a resource but does not free the handle when it is no longer used. If this occurs frequently or repeatedly over an extended period of time, a large number of handles may be marked in-use and thus unavailable, causing performance problems or a crash. The term is derived from memory leak. Handle leaks, like memory leaks, are specific instances of resource leaks. Causes One cause of a handle leak is when a programmer mistakenly believes that retrieving a handle to an entity is simply obtaining an unmanaged reference, without understanding that a count, a copy, or other operation is actually being performed. Another occurs because of poor exception handling design pattern A design pattern is the re-usable form of a solution to a design problem. The idea was introduced by the architect Christopher Alexander and has been adapted for various other disciplines, particularly software eng ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tombstone (programming)
Tombstones are a mechanism to detect dangling pointers and mitigate the problems they can cause in computer programs. Dangling pointers can appear in certain computer programming languages, e.g. C, C++ and assembly languages. A tombstone is a structure that acts as an intermediary between a pointer and its target, often heap-dynamic data in memory. The pointer – sometimes called the handle – points only at tombstones and never to its actual target. When the data is deallocated, the tombstone is set to a null (or, more generally, to a value that is illegal for a pointer in the given runtime environment), indicating that the variable no longer exists. This mechanism prevents the use of invalid pointers, which would otherwise access the memory area that once belonged to the now deallocated variable, although it may already contain other data, in turn leading to corruption of in-memory data. Depending on the operating system, the CPU can automatically detect such an invalid acc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Indirection
In computer programming, indirection (also called dereferencing) is the ability to reference something using a name, reference, or container instead of the value itself. The most common form of indirection is the act of manipulating a value through its memory address. For example, accessing a variable through the use of a pointer. A stored pointer that exists to provide a reference to an object by double indirection is called an ''indirection node''. In some older computer architectures, indirect words supported a variety of more-or-less complicated addressing modes. Another important example is the domain name system which enables names such as en.wikipedia.org to be used in place of network addresses such as 208.80.154.224. The indirection from human-readable names to network addresses means that the references to a web page become more memorable, and links do not need to change when a web site is relocated to a different server. Overview A famous aphorism of Butler Lampson ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Abstraction (computer Science)
In software engineering and computer science, abstraction is: * The process of removing or generalizing physical, spatial, or temporal details or attributes in the study of objects or systems to focus attention on details of greater importance; it is similar in nature to the process of generalization; * the creation of abstract concept-objects by mirroring common features or attributes of various non-abstract objects or systems of study – the result of the process of abstraction. Abstraction, in general, is a fundamental concept in computer science and software development. The process of abstraction can also be referred to as modeling and is closely related to the concepts of ''theory'' and ''design''. Models can also be considered types of abstractions per their generalization of aspects of reality. Abstraction in computer science is closely related to abstraction in mathematics due to their common focus on building abstractions as objects, but is also related to other ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Memory Address
In computing, a memory address is a reference to a specific memory location used at various levels by software and hardware. Memory addresses are fixed-length sequences of digits conventionally displayed and manipulated as unsigned integers. Such numerical semantic bases itself upon features of CPU (such as the instruction pointer and incremental address registers), as well upon use of the memory like an array endorsed by various programming languages. Types Physical addresses A digital computer's main memory consists of many memory locations. Each memory location has a physical address which is a code. The CPU (or other device) can use the code to access the corresponding memory location. Generally only system software, i.e. the BIOS, operating systems, and some specialized utility programs (e.g., memory testers), address physical memory using machine code operands or processor registers, instructing the CPU to direct a hardware device, called the memory controller, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
File Table
In Unix and Unix-like computer operating systems, a file descriptor (FD, less frequently fildes) is a process-unique identifier ( handle) for a file or other input/output resource, such as a pipe or network socket. File descriptors typically have non-negative integer values, with negative values being reserved to indicate "no value" or error conditions. File descriptors are a part of the POSIX API. Each Unix process (except perhaps daemons) should have three standard POSIX file descriptors, corresponding to the three standard streams: Overview In the traditional implementation of Unix, file descriptors index into a per-process maintained by the kernel, that in turn indexes into a system-wide table of files opened by all processes, called the . This table records the ''mode'' with which the file (or other resource) has been opened: for reading, writing, appending, and possibly other modes. It also indexes into a third table called the inode table that describes the actu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
