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Automatic Reference Counting
Automatic Reference Counting (ARC) is a memory management feature of the Clang compiler providing automatic reference counting for the Objective-C and Swift programming languages. At compile time, it inserts into the object code messages retain and release which increase and decrease the reference count at run time, marking for deallocation those objects when the number of references to them reaches zero. ARC differs from tracing garbage collection in that there is no background process that deallocates the objects asynchronously at runtime. Unlike tracing garbage collection, ARC does not handle reference cycles automatically. This means that as long as there are "strong" references to an object, it will not be deallocated. Strong cross-references can accordingly create deadlocks and memory leaks. It is up to the developer to break cycles by using weak references. Apple Inc. deploys ARC in their operating systems, such as macOS () and iOS. Limited support (ARCLite) has been a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Memory Management
Memory management 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. In some operating systems, e.g. OS/360 and successors, memory is managed by the operating system. In other operating systems, e.g. Unix-like operating s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Deadlock
In concurrent computing, deadlock is any situation in which no member of some group of entities can proceed because each waits for another member, including itself, to take action, such as sending a message or, more commonly, releasing a lock. Deadlocks are a common problem in multiprocessing systems, parallel computing, and distributed systems, because in these contexts systems often use software or hardware locks to arbitrate shared resources and implement process synchronization. In an operating system, a deadlock occurs when a process or thread enters a waiting state because a requested system resource is held by another waiting process, which in turn is waiting for another resource held by another waiting process. If a process remains indefinitely unable to change its state because resources requested by it are being used by another process that itself is waiting, then the system is said to be in a deadlock. In a communications system, deadlocks occur mainly due to l ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Runtime Library
In computer programming, a runtime library is a set of low-level routines used by a compiler to invoke some of the behaviors of a runtime environment, by inserting calls to the runtime library into compiled executable binary. The runtime environment implements the execution model, built-in functions, and other fundamental behaviors of a programming language. During execution (Run time (program lifecycle phase), run time) of that computer program, execution of those calls to the runtime library cause communication between the executable binary and the runtime environment. A runtime library often includes built-in functions for memory management or exception handling. Therefore, a runtime library is always specific to the platform and compiler. The runtime library may implement a portion of the runtime environment's behavior, but if one reads the code of the calls available, they are typically only thin wrappers that simply package information, and send it to the runtime enviro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
OS X Mountain Lion
OS X Mountain Lion (version 10.8) is the ninth major release of macOS, Apple Inc.'s desktop and server operating system for Macintosh computers. OS X Mountain Lion was released on July 25, 2012, for purchase and download through Apple's Mac App Store, as part of a switch to releasing OS X versions online and every year, rather than every two years or so. Named to signify its status as a refinement of the previous OS X version, Lion, Apple's stated aims in developing Mountain Lion were to allow users to more easily manage and synchronise content between multiple Apple devices and to make the operating system more familiar. The operating system gained the new malware-blocking system Gatekeeper and integration with Apple's online Game Center and iCloud services, while the Safari web browser was updated to version 6. As on iOS, Notes and Reminders became full applications, separate from Mail and Calendar, while the iChat application was replaced with a version of iOS's Messag ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
IOS 5
iOS 5 is the fifth major release of the iOS mobile operating system developed by Apple Inc., being the successor to iOS 4. It was announced at the company's Worldwide Developers Conference on June 6, 2011, and was released on October 12, 2011. It was succeeded by iOS 6 on September 19, 2012. iOS 5 revamped notifications, adding temporary banners that appear at the top of screen and introducing the Notification Center, a central location for all recent notifications. The operating system also added iCloud, Apple's cloud storage service for synchronization of content and data across iCloud-enabled devices, and iMessage, Apple's instant messaging service. For the first time, system software updates could be installed wirelessly, without requiring a computer and iTunes. iOS 5 also featured deep integration with Twitter, introduced multitasking gestures on iPads, and added an easily accessible camera shortcut from the lock screen. iOS 5 was the subject of criticism for iPhone 4S u ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mac OS X Lion
OS X Lion, also known as Mac OS X Lion, (version 10.7) is the eighth major release of macOS, Apple's desktop and server operating system for Mac computers. A preview of OS X 10.7 Lion was publicly shown at the "Back to the Mac" Apple Special Event on October 20, 2010. It brought many developments made in Apple's iOS, such as an easily navigable display of installed applications, to the Mac, and includes support for the Mac App Store, as introduced in Mac OS X 10.6 Snow Leopard version 10.6.6. On February 24, 2011, the first developer's preview of Lion (11A390) was released to subscribers to the Apple Developer program. Other developer previews were subsequently released, with Lion Preview 4 (11A480b) being released at WWDC 2011. Lion was released to manufacturing on July 1, 2011, followed by its final release via the Mac App Store on July 20, 2011. Apple reported over one million Lion sales on the first day of its release. , OS X Lion had sold over six million copies w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
IOS 4
iOS 4 is the fourth major release of the iOS mobile operating system developed by Apple Inc., being the successor to iPhone OS 3. It was announced at the Apple Special Event on April 8, 2010, and was released on June 21, 2010. iOS 4 is the first iOS version issued under the "iOS" rebranding, dropping the "iPhone OS" naming convention of previous versions. It was succeeded by iOS 5 on October 12, 2011. iOS 4 introduced folders on the home screen, significantly increasing the number of apps that can be displayed. Support for custom wallpapers was also added, although limited to newer devices due to animation performance requirements. The operating system also added a multitasking feature, letting apps dealing with Internet calling, location and audio playback function in the background, whereas a similar but more restricted "Fast App Switching" technology enabled any app to be left inactive in the background while users switch to other apps. iOS 4 also added a system-wide s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mac OS X Snow Leopard
Mac OS X Snow Leopard (version 10.6) is the seventh major release of macOS, Apple's desktop and server operating system for Macintosh computers. Snow Leopard was publicly unveiled on June 8, 2009 at Apple’s Worldwide Developers Conference. On August 28, 2009, it was released worldwide, and was made available for purchase from Apple's website and retail stores at the price of US$29 for a single-user license. As a result of the low price, initial sales of Snow Leopard were significantly higher than that of its predecessors whose price started at US$129. The release of Snow Leopard came nearly two years after the launch of Mac OS X Leopard, the second longest time span between successive Mac OS X releases (the time span between Tiger and Leopard was the longest). Unlike previous versions of Mac OS X, the goals of Snow Leopard were improved performance, greater efficiency and the reduction of its overall memory footprint. Apple famously marketed Snow Leopard as having "zero n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
MacOS
macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and laptop computers it is the second most widely used desktop OS, after Microsoft Windows and ahead of ChromeOS. macOS succeeded the classic Mac OS, a Mac operating system with nine releases from 1984 to 1999. During this time, Apple cofounder Steve Jobs had left Apple and started another company, NeXT, developing the NeXTSTEP platform that would later be acquired by Apple to form the basis of macOS. The first desktop version, Mac OS X 10.0, was released in March 2001, with its first update, 10.1, arriving later that year. All releases from Mac OS X 10.5 Leopard and after are UNIX 03 certified, with an exception for OS X 10.7 Lion. Apple's other operating systems (iOS, iPadOS, watchOS, tvOS, audioOS) are derivatives of macOS. A pro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Apple Inc
Apple Inc. is an American multinational technology company headquartered in Cupertino, California, United States. Apple is the largest technology company by revenue (totaling in 2021) and, as of June 2022, is the world's biggest company by market capitalization, the fourth-largest personal computer vendor by unit sales and second-largest mobile phone manufacturer. It is one of the Big Five American information technology companies, alongside Alphabet, Amazon, Meta, and Microsoft. Apple was founded as Apple Computer Company on April 1, 1976, by Steve Wozniak, Steve Jobs and Ronald Wayne to develop and sell Wozniak's Apple I personal computer. It was incorporated by Jobs and Wozniak as Apple Computer, Inc. in 1977 and the company's next computer, the Apple II, became a best seller and one of the first mass-produced microcomputers. Apple went public in 1980 to instant financial success. The company developed computers featuring innovative graphical user inte ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Weak Reference
In computer programming, a weak reference is a reference that does not protect the referenced object from collection by a garbage collector, unlike a strong reference. An object referenced ''only'' by weak references – meaning "every chain of references that reaches the object includes at least one weak reference as a link" – is considered ''weakly reachable,'' and can be treated as unreachable and so may be collected at any time. Some garbage-collected languages feature or support various levels of weak references, such as C#, Java, Lisp, OCaml, Perl, Python and PHP since the version 7.4. Uses Weak references have a number of common uses. When using reference counting garbage collection, weak references can break reference cycles, by using a weak reference for a link in the cycle. When one has an associative array (mapping, hash map) whose keys are (references to) objects, for example to hold auxiliary data about objects, using weak references for the keys avoids keeping th ... [...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] |
