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Sbrk
and are basic memory management system calls used in Unix and Unix-like operating systems to control the amount of memory allocated to the heap segment of the process. These functions are typically called from a higher-level memory management library function such as . In the original Unix system, and were the only ways in which applications could acquire additional heap space; later versions allowed this to also be done using the call. Description The brk and sbrk calls dynamically change the amount of space allocated for the heap segment of the calling process. The change is made by resetting the program break of the process, which determines the maximum space that can be allocated. The program break is the address of the first location beyond the current end of the data region. The amount of available space increases as the break value increases. The available space is initialized to a value of zero, unless the break is lowered and then increased, as it may reuse the sam ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Memory Management
Memory management (also dynamic memory management, dynamic storage allocation, or dynamic memory allocation) is a form of Resource management (computing), resource management applied to computer memory. The essential requirement of memory management is to provide ways to dynamically allocate portions of memory to programs at their request, and free it for reuse when no longer needed. This is critical to any advanced computer system where more than a single Process (computing), process might be underway at any time. Several methods have been devised that increase the effectiveness of memory management. Virtual memory systems separate the memory addresses used by a process from actual physical addresses, allowing separation of processes and increasing the size of the virtual address space beyond the available amount of Random-access memory, RAM using paging or swapping to secondary storage. The quality of the virtual memory manager can have an extensive effect on overall system C ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
System Call
In computing, a system call (syscall) is the programmatic way in which a computer program requests a service from the operating system on which it is executed. This may include hardware-related services (for example, accessing a hard disk drive or accessing the device's camera), creation and execution of new processes, and communication with integral kernel services such as process scheduling. System calls provide an essential interface between a process and the operating system. In most systems, system calls can only be made from userspace processes, while in some systems, OS/360 and successors for example, privileged system code also issues system calls. For embedded systems, system calls typically do not change the privilege mode of the CPU. Privileges The architecture of most modern processors, with the exception of some embedded systems, involves a security model. For example, the '' rings'' model specifies multiple privilege levels under which software may be e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Unix
Unix (, ; trademarked as UNIX) is a family of multitasking, multi-user computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and others. Initially intended for use inside the Bell System, AT&T licensed Unix to outside parties in the late 1970s, leading to a variety of both academic and commercial Unix variants from vendors including University of California, Berkeley ( BSD), Microsoft (Xenix), Sun Microsystems ( SunOS/ Solaris), HP/ HPE ( HP-UX), and IBM ( AIX). The early versions of Unix—which are retrospectively referred to as " Research Unix"—ran on computers such as the PDP-11 and VAX; Unix was commonly used on minicomputers and mainframes from the 1970s onwards. It distinguished itself from its predecessors as the first portable operating system: almost the entire operating system is written in the C programming language (in 1973), which allows U ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Unix-like
A Unix-like (sometimes referred to as UN*X, *nix or *NIX) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-like Application software, application is one that behaves like the corresponding List of POSIX commands, Unix command or Unix shell, shell. Although there are general Unix philosophy, philosophies for Unix design, there is no technical standard defining the term, and opinions can differ about the degree to which a particular operating system or application is Unix-like. Some well-known examples of Unix-like operating systems include Linux, FreeBSD and OpenBSD. These systems are often used on servers as well as on personal computers and other devices. Many popular applications, such as the Apache HTTP Server, Apache web server and the Bash (Unix shell), Bash shell, are also designed to be used on Unix-like systems. Definition The Open ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Process (computing)
In computing, a process is the Instance (computer science), instance of a computer program that is being executed by one or many thread (computing), threads. There are many different process models, some of which are light weight, but almost all processes (even entire virtual machines) are rooted in an operating system (OS) process which comprises the program code, assigned system resources, physical and logical access permissions, and data structures to initiate, control and coordinate execution activity. Depending on the OS, a process may be made up of multiple threads of execution that execute instructions Concurrency (computer science), concurrently. While a computer program is a passive collection of Instruction set, instructions typically stored in a file on disk, a process is the execution of those instructions after being loaded from the disk into memory. Several processes may be associated with the same program; for example, opening up several instances of the same progra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Malloc
C dynamic memory allocation refers to performing manual memory management for dynamic memory allocation in the C programming language via a group of functions in the C standard library, namely , , , and . The C++ programming language includes these functions; however, the operators and provide similar functionality and are recommended by that language's authors. Still, there are several situations in which using new/delete is not applicable, such as garbage collection code or performance-sensitive code, and a combination of malloc and placement new may be required instead of the higher-level new operator. Many different implementations of the actual memory allocation mechanism, used by , are available. Their performance varies in both execution time and required memory. Rationale The C programming language manages memory statically, automatically, or dynamically. Static-duration variables are allocated in main memory, usually along with the executable code of th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mmap
In computing, mmap(2) is a POSIX-compliant Unix system call that maps files or devices into memory. It is a method of memory-mapped file I/O. It implements demand paging because file contents are not immediately read from disk and initially use no physical RAM at all. The actual reads from disk are performed after a specific location is accessed, in a lazy manner. After the mapping is no longer needed, the pointers must be unmapped with munmap(2). Protection information—for example, marking mapped regions as executable—can be managed using mprotect(2), and special treatment can be enforced using madvise(2). In Linux, macOS and the BSDs, mmap can create several types of mappings. Other operating systems may only support a subset of these; for example, shared mappings may not be practical in an operating system without a global VFS or I/O cache. History The original design of memory-mapped files came from the TOPS-20 operating system. mmap and associated systems calls were de ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dynamic Memory Allocation
Memory management (also dynamic memory management, dynamic storage allocation, or dynamic memory allocation) is a form of resource management applied to computer memory. The essential requirement of memory management is to provide ways to dynamically allocate portions of memory to programs at their request, and free it for reuse when no longer needed. This is critical to any advanced computer system where more than a single process might be underway at any time. Several methods have been devised that increase the effectiveness of memory management. Virtual memory systems separate the memory addresses used by a process from actual physical addresses, allowing separation of processes and increasing the size of the virtual address space beyond the available amount of RAM using paging or swapping to secondary storage. The quality of the virtual memory manager can have an extensive effect on overall system performance. The system allows a computer to appear as if it may have more ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Single UNIX Specification
The Single UNIX Specification (SUS) is a standard for computer operating systems, compliance with which is required to qualify for using the "UNIX" trademark. The standard specifies programming interfaces for the C language, a command-line shell, and user commands. The core specifications of the SUS known as ''Base Specifications'' are developed and maintained by the Austin Group, which is a joint working group of IEEE, ISO/IEC JTC 1/SC 22/WG 15 and The Open Group. If an operating system is submitted to The Open Group for certification and passes conformance tests, then it is deemed to be compliant with a UNIX standard such as UNIX 98 or UNIX 03. Very few BSD and Linux-based operating systems are submitted for compliance with the Single UNIX Specification, although system developers generally aim for compliance with POSIX standards, which form the core of the Single UNIX Specification. The latest SUS consists of two parts: the ''base specifications'' technically iden ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Errno
errno.h is a header file in the standard library of the C programming language. It defines macros for reporting and retrieving error conditions using the symbol errno (short form for "error number").International Standard for Programming Language C (C11), ISO/IEC 9899:2011, p. 205 errno acts like an integer variable. A value (the error number) is stored in errno by certain library functions when they detect errors. At program startup, the value stored is zero. Library functions store only values greater than zero. Any library function can alter the value stored before return, whether or not they detect errors.International Standard for Programming Language C (C99), ISO/IEC 9899:1999, p. 186 Most functions indicate that they detected an error by returning a special value, typically NULL for functions that return pointers, and -1 for functions that return integers. A few functions require the caller to preset errno to zero and test it afterwards to see if an error was detected. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Global Variable
In computer programming, a global variable is a variable with global scope, meaning that it is visible (hence accessible) throughout the program, unless shadowed. The set of all global variables is known as the ''global environment'' or ''global state.'' In compiled languages, global variables are generally static variables, whose extent (lifetime) is the entire runtime of the program, though in interpreted languages (including command-line interpreters), global variables are generally dynamically allocated when declared, since they are not known ahead of time. In some languages, all variables are global, or global by default, while in most modern languages variables have limited scope, generally lexical scope, though global variables are often available by declaring a variable at the top level of the program. In other languages, however, global variables do not exist; these are generally modular programming languages that enforce a module structure, or class-based object-or ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mac OS X
macOS, previously OS X and originally Mac OS X, is a Unix, Unix-based operating system developed and marketed by Apple Inc., Apple since 2001. It is the current operating system for Apple's Mac (computer), Mac computers. Within the market of Desktop computer, desktop and laptop computers, it is the Usage share of operating systems#Desktop and laptop computers, second most widely used desktop OS, after Microsoft Windows and ahead of all Linux distributions, including ChromeOS and SteamOS. , the most recent release of macOS is MacOS Sequoia, macOS 15 Sequoia, the 21st major version of macOS. Mac OS X succeeded classic Mac OS, the primary Mac operating systems, Macintosh operating system from 1984 to 2001. Its underlying architecture came from NeXT's NeXTSTEP, as a result of NeXT#1997–2006: Acquisition by Apple, Apple's acquisition of NeXT, which also brought Steve Jobs back to Apple. The first desktop version, Mac OS X 10.0, was released on March 24, 2001. Mac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
