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1. Concurrent (of concurrence) . 1
Concurrency : refers to two or more events occur within the same time interval. These macro events occur simultaneously, but the micro is alternately occur.
Test often confusing concept -parallel: Refers to two or more events occur simultaneously at the same time.
Parallel concurrent VS
exp: Let's assume the old slag and slag each have two girlfriends. Task One: One and appointments; Task Two: II and dating ...
Concurrent appointments: Sub-period and the number one and two appointments. . . One morning and date, and number two in the afternoon appointments.
Parallel Dating: And one and two on a double date
Concurrent operating systems : refer to a computer system there are a plurality of simultaneously running programs.
A single-core processor(CPU) can only execute one program at a time, so the operating system will be responsible for coordinating multiple programs performed alternately (micro alternating execution of these programs, but the macro looks like while performing)
Whether a few core CPU, operating system concurrency is still essential.
2. Sharing (sharing)
That shared resource sharing, refers to the process of system memory resources available in multiple concurrent execution of common use.
Two resources sharing:
Exclusive sharing: Some resources in the system, although you can provide multiple processes to use, but a period of time only allows a process to access the resource.
At the same time sharing: Some resources in the system, allowing a period of time "while" they are accessed by multiple processes. The so-called "simultaneous" is often macroscopically, but microscopically, these processes may be alternately access the resources (ie, time-share)
Life examples :
exclusive sharing: use QQ and micro-channel video. The same period of time the camera can only be assigned to one of the processes.
While sharing manner: send the file using QQ A, file transmission while using the micro-channel B. Macro point of view, both sides are simultaneously read and send the file, that the two processes are accessing the hard disk resource from which to read the data. Microscopic point of view, the two processes are alternately access the hard disk.
Note: speakers, game sound effects and music player, the micro is used simultaneously.
The relationship between concurrency and shared
Concurrency refers to a computer system there are a plurality of simultaneously running programs.
Sharing refers to the process in the system memory resources available in multiple concurrent execution of common use.
Concurrent with the relationship shared view of the example described above:
use QQ send the file A, the file transmission while using the micro-channel B.
1. The two processes are executed concurrently (concurrency) . If you lose concurrency, the system has only one program is running, the sharing of meaningless existence.
2. The need to share access to the hard disk resources (sharing) . If you lose sharing, and the QQ micro letter you can not access hard disk resources can not be achieved at the same time send the file, it can not concurrent.
The presence of concurrency and sharing each other
3. Virtual (virtual)
Virtual refers to a physical entity on the counterpart becomes several logical. There is a real physical entity, and the corresponding logical object is perceived by the user.
Background : A program needs into memory and assigned CPU can execute.
Virtual technology is divided into:
Space division multiplexing(E.g., virtual storage technology)
TDM technology(Such as virtual processors): the micro processor at each turn of the small period of time for each process services.
Obviously, if the loss of concurrency, then a period of time the system simply run a program, then lost the meaning of the virtual. Therefore, it would not be no concurrency virtual sex.
4. Asynchronous (asynchronism)
Asynchronous means that in a multi-channel programming environment that allows concurrent execution of multiple programs, but due to limited resources, the implementation process is not consistent in the end, but stop and go, in order to move forward at an unpredictable rate, which is the asynchronous nature .
Obviously, if the loss of concurrency, the system can only be serially processing each process, the implementation of each process will be consistent in the end.The system has only concurrency, asynchrony possible cause。
Important test sites:
understanding the difference between concurrency and parallelism of
concurrent and mutually shared presence
No concurrency and shared, it would not virtual and asynchronous, concurrent, and therefore share two basic features of the operating system
All the above are benevolent finishing from PubMed ↩︎
