Room # Linux # # System V IPC Standard & POSIX standard

When interprocess communication system linux, for example, find the shared memory, semaphores, message queues, shared manner among other processes, often find System v POXIS two types are provided and their solutions.

 

POSIX

POSIX (Portable Operating System Interface for Computing Systems) prepared by the IEEE and ISO / IEC standards developed cluster. The standard is based on the existing UNIX practices and experience, describes the operation of the system calls the service interface to ensure that the application can be compiled to run on the source code for a transplant on a variety of operating systems. It is made on the basis of earlier work early in 1980, a UNIX user group (usr / group) on. The UNIX user attempts to set the difference between the original call interface AT & T System V and Berkeley CSRG reconciliation between the BSD system integration, resulting in the / usr / group 1984 standard. In 1985, IEEE Technical Committee on Operating Systems Standards Subcommittee (TCOS-SS) began to instruct the support of the ANSI IEEE standards established by the Committee about the program source code portability official standard operating system service interface. To April 1986, IEEE will work out a trial standards. The first official standard was approved in September 1988 (IEEE 1003.1-1988), both POSIX.1 standard also frequently mentioned later.

 

System V

System V, who is also known as AT & T System V, is one of many versions of the Unix operating system a. It is early, first released by AT & T to develop in 1983. Issued a total of four major releases of System V: versions 2, 3 and 4. System V Release 4, otherwise known as SVR4, was successful editions, is the source of some of the common features of UNIX, such as "SysV init scripts" (/etc/init.d), used to control the system startup and shutdown, System V Interface Definition (SVID) is a standard that defines how a System V work.

AT & T System V sale of proprietary hardware to run, but many (perhaps most) customers on which to run a resale version, this version is based on AT & T's implementation notes. Popular SysV derivatives include Dell SVR4 version and Bull SVR4. System V version of the widely used today is SCO OpenServer, based on System V Release 3, and SUN Solaris and SCO UnixWare, are based on System V Release 4.

AT & T System V is the first commercial version of UNIX (UNIX System III) strengthened. Traditionally, System V is seen as "flavor" one of the two UNIX (the other is BSD). However, with some of the code is not UNIX-based implementations of both appear, such as Linux and QNX, this induction is no longer accurate, but no matter how, standardization efforts such as POSIX been trying to reduce between various implementations of different.

The difference between the two, we simply make a simple comparison of the following dimensions

history

• V System:  UNIX two major contributors Bell Laboratories and BSD, communication between processes of different emphases, the former has been improved based on the means of communication between the kernel process, forming a "System V IPC", while the latter is based on the network forming a socket socket.
• The POSIX:  the IEEE standards developed in order to provide uniform software to run on different operating systems interface implementer is a different operating system kernel developers.

Efficiency performance

• V System:  PSYSTEM V synchronization means mutually exclusive aspects of free competition conditions would fall into that whenever the kernel, slightly lower performance.
• The POSIX: the POSIX synchronization means mutually exclusive aspects of the non-competitive conditions will not fall into the core, high performance somewhat less.

Redundant reliability

• V System:  System V provides SEM_UNDO option to acquire the semaphore successfully resolved, if the process terminates unexpectedly, it can not release the semaphore problem. High reliability.
• POSIX: After the sem_wait POSIX function successfully acquired the semaphore, if the process terminates unexpectedly, it can not release the semaphore. Poor reliability.

operating system

• V System:  System V operating system to achieve a wide range.
• POSIX: There may be a small part of the operating system does not implement the POSIX standard.

Portability

• System V:  Different System V operating system, there are some differences.
• POSIX: Portability POSIX is an inevitable trend.

Interprocess communication between & Thread Synchronization

• V System: System V more for inter-process communication, inter-thread use less. Thread is lightweight relative to the process, such as scheduling strategy overhead, if you use System V this fall will each call interface to the kernel, it will lose the advantages of lightweight threads. Therefore, the communication between the multi-thread interface function is not used in System V
• POSIX: POSIX Interprocess communication & inter-thread synchronization better.

 

POSIX standards are gradually replacing the standard System V trends