How to Run Same Task Again C

Concurrent execution of multiple processes

Modern desktop operating systems are capable of handling big numbers of different processes at the aforementioned time. This screenshot shows Linux Mint running simultaneously Xfce desktop environs, Firefox, a calculator program, the built-in calendar, Vim, GIMP, and VLC media histrion.

Multitasking of Microsoft Windows 1.01 released in 1985, hither shown running the MS-DOS Executive and Figurer programs

In computing, multitasking is the concurrent execution of multiple tasks (also known as processes) over a certain period of fourth dimension. New tasks can interrupt already started ones before they finish, instead of waiting for them to end. As a event, a computer executes segments of multiple tasks in an interleaved style, while the tasks share mutual processing resource such as central processing units (CPUs) and main memory. Multitasking automatically interrupts the running program, saving its state (fractional results, retention contents and computer register contents) and loading the saved state of another program and transferring control to it. This "context switch" may be initiated at stock-still fourth dimension intervals (pre-emptive multitasking), or the running program may be coded to signal to the supervisory software when it can be interrupted (cooperative multitasking).

Multitasking does non crave parallel execution of multiple tasks at exactly the same fourth dimension; instead, it allows more than than one task to advance over a given flow of time.^[1] Even on multiprocessor computers, multitasking allows many more tasks to be run than there are CPUs.

Multitasking is a common feature of reckoner operating systems since at least the 1960s. Information technology allows more than efficient use of the computer hardware; where a program is waiting for some external outcome such as a user input or an input/output transfer with a peripheral to complete, the central processor tin can notwithstanding be used with another program. In a fourth dimension-sharing system, multiple human operators use the same processor as if it was dedicated to their utilise, while backside the scenes the calculator is serving many users by multitasking their individual programs. In multiprogramming systems, a job runs until it must wait for an external result or until the operating system's scheduler forcibly swaps the running task out of the CPU. Real-fourth dimension systems such as those designed to control industrial robots, crave timely processing; a single processor might be shared between calculations of machine movement, communications, and user interface.^[ii]

Often multitasking operating systems include measures to change the priority of private tasks, so that important jobs receive more processor fourth dimension than those considered less pregnant. Depending on the operating organization, a task might exist as large equally an entire application program, or might be made up of smaller threads that bear out portions of the overall program.

A processor intended for use with multitasking operating systems may include special hardware to securely support multiple tasks, such as retentivity protection, and protection rings that ensure the supervisory software cannot be damaged or subverted by user-style programme errors.

The term "multitasking" has get an international term, as the same word is used in many other languages such every bit German, Italian, Dutch, Romanian, Czech, Danish and Norwegian.

Multiprogramming [edit]

In the early days of calculating, CPU fourth dimension was expensive, and peripherals were very slow. When the computer ran a program that needed access to a peripheral, the central processing unit (CPU) would take to terminate executing plan instructions while the peripheral candy the data. This was usually very inefficient.

The first reckoner using a multiprogramming system was the British Leo III endemic by J. Lyons and Co. During batch processing, several dissimilar programs were loaded in the figurer memory, and the commencement one began to run. When the kickoff programme reached an teaching waiting for a peripheral, the context of this programme was stored away, and the second program in memory was given a chance to run. The process continued until all programs finished running.^[3]

The utilize of multiprogramming was enhanced by the inflow of virtual memory and virtual machine applied science, which enabled individual programs to brand use of memory and operating system resources every bit if other concurrently running programs were, for all practical purposes, nonexistent.^{[ citation needed ]}

Multiprogramming gives no guarantee that a programme will run in a timely mode. Indeed, the first plan may very well run for hours without needing access to a peripheral. As there were no users waiting at an interactive final, this was no problem: users handed in a deck of punched cards to an operator, and came back a few hours later for printed results. Multiprogramming greatly reduced wait times when multiple batches were being processed.^{[4] [v]}

Cooperative multitasking [edit]

Early multitasking systems used applications that voluntarily ceded time to one some other. This approach, which was eventually supported past many figurer operating systems, is known today as cooperative multitasking. Although information technology is at present rarely used in larger systems except for specific applications such as CICS or the JES2 subsystem, cooperative multitasking was in one case the only scheduling scheme employed past Microsoft Windows and classic Mac OS to enable multiple applications to run simultaneously. Cooperative multitasking is still used today on RISC OS systems.^[6]

As a cooperatively multitasked arrangement relies on each process regularly giving up fourth dimension to other processes on the arrangement, one poorly designed plan tin eat all of the CPU time for itself, either by performing extensive calculations or by busy waiting; both would cause the whole system to hang. In a server surroundings, this is a gamble that makes the unabridged environment unacceptably fragile.

Preemptive multitasking [edit]

Preemptive multitasking allows the computer organisation to more than reliably guarantee to each process a regular "piece" of operating fourth dimension. It also allows the organization to deal speedily with important external events like incoming data, which might require the immediate attention of 1 or another process. Operating systems were developed to accept advantage of these hardware capabilities and run multiple processes preemptively. Preemptive multitasking was implemented in the PDP-6 Monitor and MULTICS in 1964, in Os/360 MFT in 1967, and in Unix in 1969, and was available in some operating systems for computers equally small as December's PDP-8; information technology is a core characteristic of all Unix-like operating systems, such every bit Linux, Solaris and BSD with its derivatives,^[seven] every bit well every bit mod versions of Windows.

At any specific time, processes tin can exist grouped into two categories: those that are waiting for input or output (called "I/O bound"), and those that are fully utilizing the CPU ("CPU spring"). In primitive systems, the software would often "poll", or "busywait" while waiting for requested input (such every bit disk, keyboard or network input). During this time, the system was not performing useful piece of work. With the advent of interrupts and preemptive multitasking, I/O bound processes could be "blocked", or put on hold, pending the arrival of the necessary data, allowing other processes to utilize the CPU. As the arrival of the requested information would generate an interrupt, blocked processes could be guaranteed a timely render to execution.^{[ commendation needed ]}

The earliest preemptive multitasking Bone available to home users was Sinclair QDOS on the Sinclair QL, released in 1984, but very few people bought the auto. Commodore's Amiga, released the following twelvemonth, was the first commercially successful home reckoner to utilize the technology, and its multimedia abilities make it a clear ancestor of contemporary multitasking personal computers. Microsoft made preemptive multitasking a core feature of their flagship operating system in the early 1990s when developing Windows NT 3.ane then Windows 95. It was subsequently adopted on the Apple tree Macintosh by Mac Os Ten that, as a Unix-similar operating system, uses preemptive multitasking for all native applications.

A similar model is used in Windows 9x and the Windows NT family, where native 32-bit applications are multitasked preemptively.^[8] 64-fleck editions of Windows, both for the x86-64 and Itanium architectures, no longer back up legacy sixteen-chip applications, and thus provide preemptive multitasking for all supported applications.

Real time [edit]

Another reason for multitasking was in the blueprint of existent-time calculating systems, where there are a number of mayhap unrelated external activities needed to exist controlled by a single processor arrangement. In such systems a hierarchical interrupt system is coupled with procedure prioritization to ensure that key activities were given a greater share of available process fourth dimension.^[9]

Multithreading [edit]

As multitasking profoundly improved the throughput of computers, programmers started to implement applications as sets of cooperating processes (e. g., one process gathering input data, one process processing input data, one procedure writing out results on disk). This, however, required some tools to allow processes to efficiently exchange data.^{[ commendation needed ]}

Threads were born from the idea that the most efficient way for cooperating processes to substitution data would be to share their entire memory infinite. Thus, threads are effectively processes that run in the same retentivity context and share other resources with their parent processes, such as open up files. Threads are described as lightweight processes because switching between threads does not involve changing the memory context.^{[10] [eleven] [12]}

While threads are scheduled preemptively, some operating systems provide a variant to threads, named fibers, that are scheduled cooperatively. On operating systems that exercise not provide fibers, an awarding may implement its ain fibers using repeated calls to worker functions. Fibers are even more than lightweight than threads, and somewhat easier to program with, although they tend to lose some or all of the benefits of threads on machines with multiple processors.^[xiii]

Some systems directly support multithreading in hardware.

Retention protection [edit]

Essential to any multitasking organisation is to safely and finer share access to system resources. Access to memory must be strictly managed to ensure that no procedure tin inadvertently or deliberately read or write to retentiveness locations exterior the process's address space. This is done for the purpose of full general system stability and data integrity, likewise as data security.

In general, memory admission management is a responsibleness of the operating system kernel, in combination with hardware mechanisms that provide supporting functionalities, such as a memory management unit (MMU). If a process attempts to access a memory location outside its memory space, the MMU denies the request and signals the kernel to take appropriate actions; this usually results in forcibly terminating the offending procedure. Depending on the software and kernel design and the specific error in question, the user may receive an access violation error message such equally "segmentation error".

In a well designed and correctly implemented multitasking system, a given procedure can never straight admission retentiveness that belongs to another process. An exception to this rule is in the example of shared retentiveness; for example, in the System Five inter-process communication mechanism the kernel allocates retentiveness to exist mutually shared by multiple processes. Such features are ofttimes used by database management software such as PostgreSQL.

Inadequate retention protection mechanisms, either due to flaws in their design or poor implementations, permit for security vulnerabilities that may be potentially exploited by malicious software.

Memory swapping [edit]

Use of a swap file or swap partition is a way for the operating system to provide more memory than is physically bachelor by keeping portions of the primary retentivity in secondary storage. While multitasking and memory swapping are 2 completely unrelated techniques, they are very frequently used together, as swapping memory allows more tasks to be loaded at the same fourth dimension. Typically, a multitasking system allows another process to run when the running process hits a signal where it has to wait for some portion of memory to exist reloaded from secondary storage.^[14]

Programming [edit]

Processes that are entirely independent are not much trouble to plan in a multitasking surroundings. Almost of the complexity in multitasking systems comes from the need to share figurer resources betwixt tasks and to synchronize the operation of co-operating tasks.^{[ citation needed ]}

Various concurrent calculating techniques are used to avoid potential problems caused by multiple tasks attempting to admission the same resource.^{[ citation needed ]}

Bigger systems were sometimes built with a fundamental processor(s) and some number of I/O processors, a kind of disproportionate multiprocessing.^{[ citation needed ]}

Over the years, multitasking systems have been refined. Modern operating systems generally include detailed mechanisms for prioritizing processes, while symmetric multiprocessing has introduced new complexities and capabilities.^[15]

Come across also [edit]

• Procedure state
• Task switching

References [edit]

1. ^ "Concurrency vs Parallelism, Concurrent Programming vs Parallel Programming". Oracle. Archived from the original on April seven, 2016. Retrieved March 23, 2016.
2. ^ Anthony Ralston, Edwin D. Reilly (ed),Encyclopedia of Computer Science Third Edition, Van Nostrand Reinhold, 1993, ISBN 0-442-27679-6, articles "Multitasking" and "Multiprogramming"
3. ^ MASTER PROGRAME AND PROGRAMME TRIALS SYSTEM PART 1 MASTER Program SPECIFICATION. February 1965. section 6 "PRIORITY Command ROUTINES".
4. ^ Lithmee (2019-05-20). "What is the Difference Between Batch Processing and Multiprogramming". Pediaa.Com . Retrieved 2020-04-14 .
5. ^ "Evolution of Operating System". 2017-09-29. Retrieved 2020-04-14 .
6. ^ "Preemptive multitasking". riscos.info. 2009-11-03. Retrieved 2014-07-27 .
7. ^ "UNIX, Office One". The Digital Research Initiative. ibiblio.org. 2002-01-30. Retrieved 2014-01-09 .
8. ^ Joseph Moran (June 2006). "Windows 2000 &16-Fleck Applications". Smart Calculating. Vol. sixteen, no. half-dozen. pp. 32–33. Archived from the original on Jan 25, 2009.
9. ^ Liu, C. L.; Layland, James W. (1973-01-01). "Scheduling Algorithms for Multiprogramming in a Hard-Existent-Time Environment". Periodical of the ACM. 20 (1): 46–61. doi:ten.1145/321738.321743. ISSN 0004-5411.
10. ^ Eduardo Ciliendo; Takechika Kunimasa (April 25, 2008). "Linux Performance and Tuning Guidelines" (PDF). redbooks.ibm.com. IBM. p. 4. Archived from the original (PDF) on February 26, 2015. Retrieved March 1, 2015.
11. ^ "Context Switch Definition". linfo.org. May 28, 2006. Archived from the original on February 18, 2010. Retrieved February 26, 2015.
12. ^ "What are threads (user/kernel)?". tldp.org. September viii, 1997. Retrieved February 26, 2015.
13. ^ Multitasking different methods Accessed on February 19, 2019
14. ^ "What is a swap file?". kb.iu.edu . Retrieved 2018-03-26 .
15. ^ "Operating Systems Architecture". cis2.oc.ctc.edu . Retrieved 2018-03-17 .

greensatifer.blogspot.com

Source: https://en.wikipedia.org/wiki/Computer_multitasking

Share this post