COMP 3000 Essay 1 2010 Question 8

QUESTION

What is the history of POSIX Threads (pthreads)? Consider - does this history explain why UNIX was so late to implement support for multithreaded processes?

ESSAY

INTRODUCTION

POSIX threads, also known as Portable Operating System Interface, are high performance threads mainly distributed in UNIX but also to some Microsoft Windows OS. Threads are used in parallel programming; when a system call executes, the thread runs on an independent stream to finish its task with minimal interruptions or slowdowns. Pthreads are ideal for massive modifications to programs because the threads share one single memory space to alter a data structure, allowing constant high performance and efficiency. Pthread has become commonly used a way of adding concurrency to an application. They are widely used in UNIX; a powerful operating system written in the C language, which is continuously enhanced. Developers came across various obstacles with POSIX threads; during the beginnings of Pthreads, many technical issues had surfaced which were resolved throughout the history of POSIX threads.

HISTORY

UNIX

UNIX, the widely-known multi-user and multitasking computer operating system, was originally developed in 1969. The UNIX OS is trademarked is owned by The Open group and the specification is freely available on the worldwide web. The first official version of UNIX ran in 1970, on a PDP-11/20 machine; the first of the series called PDP-11 of compatible systems. This machine consisted of a text formatting program called 'ROFF' and a text editor. ROFF was the first UNIX text-formatting computer program;[1] it was rewritten in 1972, in a programming language called C which internally brought forth a number of portable software. The standard C programming language became available to Universities, colleges, commercial firms, as well as the US Government. UNIX was progressing rapidly; many editions of UNIX were introduced by 1975, and versions 4.5 and 4.6 were distributed to the users.[2] Newer versions added the notion of ‘pipes’ which lead to numerous modular code-base and faster development cycle. Pipeline is essentially a chain of processes combined together by streams. As a result, the output of one process is the input of the following. UNIX became increasingly portable resulting in the release of Version 7 in 1979, followed by several more versions (8, 9, and 10) released in the 1980’s.

UNIX has progressed at an astounding pace in the past few years; early UNIX had a ‘process’ which was a thread of control with a virtual address space, and the interaction was through pipes due to the inability of sharing. After a while, the advancement of UNIX lead to processes that shared memory, introducing the invention of the thread. The threads are referred to as lightweight threads, in contrast to the heavyweight processes before it.

THREADS/PTHREADS

The notion of threads was developed naturally out of the desire for processes to communicate with each other. Threads are at a basic level of multiple threads of control that share memory, which is a relatively instantaneous method of communication. In UNIX, where processes were seen as a 1:1 per-terminal basis, and more about time-sharing than working together, at first this seemed relatively unnecessary [3]. Retrieved on October 14 2010</ref>. They were after all, mechanisms in place to communicate between processes such as pipes and temporary files, as well as a few "just changed" messages. The first UNIX implementation of shared memory came about in 1983 with the System V UNIX flavour, which shared memory and was merely one of the several upgrades for passing messages between processes. [4]

The alternative Pthread implementation in the 4.0 Digital UNIX, also known as DEC OSF/1, which was a part of the Mach operating system. Pthread library schedules’ threads consist of a one-to-one relationship; all threads fight other threads excluding the threads with the same process. This is good for priority, there is a positive correlation between priority and function; if priority rises, so does the function of the specific process. Many threads in a program have the ability to run on different CPUs, this prevents a program from being limited to a single executing thread. Native POSIX Thread Library is also known as NPTL which was first released in Red Hat Linux 9. This software enables the Linux kernel to run programs efficiently using POSIX threads.[5] Version 1 of NPTL was released in 1996, followed by other versions leading up to version 2.6 recently. NPTL has become a part of the Linux kernel since version 2.6. To this day, threads in Linux are still created with the clone() system call in the Java programming language, although they are abstracted away in the actual language. Futexes are the newest evolution of mutexes in the Linux kernal and are the foundation of many mutual exclusion constructs that are frequently used in threaded programming. Despite the growing progress in Pthreads there have been many technical issues which lead to late implementation of support for multithread processes.[6]

COMPLICATIONS

The beginning of POSIX Threads starts off with hardware sellers executing their own versions of threads. These developments varied from one another, creating difficulties for programmers to implement portable thread applications[7]. With UNIX starting to develop shared memory as a viable Inter-process communication tool developers started to create a high demand for the ability to run multiple threads under one process. Consequently, IEEE began to form together the POSIX standards. In 1988, POSIX.1 - created to support application portability – was ratified and accepted as the international standard in 1990[8]. After the approval, the POSIX standard grew to more than 20 individual standards, encapsulating a large area of different groups.

POSIX.1 lays out the interfaces for OS services; their syntax, and how they should act. However, it does not define how the interface should be implemented on the OS, allowing many different operating systems to conform to standards in their own specific design and application. POSIX.2 was created for much of the same reason as POSIX.1; portable shell programming and portable program development, but describes a programmable shell and its common utilities[9]. Although POSIX.2 improved on the original, POSIX threading has always been an issue on Linux. UNIX was so late to implement support for multithreaded process because it does not map that well onto Linux; this is due to the significant differences in relationship between POSIX and UNIX. These differences include: naming conventions (identifiers, operators, etc...), parameters and variables.[10]

CONCLUSION

In the last twenty years, several advancements took place; there was a huge leap from the basic performance and function of a standard thread to a multi-threading, high performance POSIX thread. However, before it was given recognition as being efficient with high performance, a POSIX thread had numerous setbacks and high-priority challenges. Although the basic principle of a POSIX thread within UNIX was already executed by hardware sellers, it was under different names with minor structural variations, prohibiting developers to create portable thread applications. Fortunately, these issues were resolved and POSIX threads were enhanced, with continuous improvements on the way. Developers made an extraordinary breakthrough in concurrent programming by enabling efficiency and high performance, especially during immense modifications to data structure. Even with a rough past, POSIX threads have improved to become one of the most widely-known and commonly used method of adding concurrency to an application.

SOURCES

[1] Dennis M. Ritchie, 1996. Bell Laboratoeries, The Evolution of the UNIX Time-Sharing System. online at: <http://cm.bell-labs.com/cm/cs/who/dmr/hist.html>

[2] Éric Lévénez, September 2010. Unix History. online at: <http://www.levenez.com/unix/>

[3] David Sweet, 2001. Sams Publishing, KDE 2.0 Development. online at:<http://tinf2.vub.ac.be/~dvermeir/manuals/KDE20Development-html/ch13lev1sec2.html>

[4] Mike Perry, September 1999. Shared Memory Under Linux. online at: <http://fscked.org/writings/SHM/shm-5.html>

[5] Janice J. Heiss, 2003. Oracle. Red Hat Linux 9 and Java 2 Platform, Standard Edition 1.4.2: A Winning Combination. online at: <http://java.sun.com/developer/technicalArticles/JavaTechandLinux/RedHat/>

[6] Robert Love, 2003. Introducing the 2.6 Kernel. online at: <http://www.linuxjournal.com/article/6530>

[7] Blaise Barney, 2010. Lawrence Livermore National Laboratory. POSIX Threads Programming. online at: <https://computing.llnl.gov/tutorials/pthreads/>

[8] Andrew Josey, February 2006, The Open Group. POSIX 1003.1 FAQ. online at: <http://www.opengroup.org/austin/papers/posix_faq.html>

[9] Link currently down, was online at: <http://delivery.acm.org/10.1145/220000/210315/p11-walli.pdf?key1=210315&key2=0607607821&coll=GUIDE&dl=GUIDE&CFID=108396689&CFTOKEN=35895091>

[10] Link currently down, was online at: <http://delivery.acm.org/10.1145/220000/210315/p11-walli.pdf?key1=210315&key2=0607607821&coll=GUIDE&dl=GUIDE&CFID=108396689&CFTOKEN=35895091>

[11] Blaise Barney, 2010. Lawrence Livermore National Laboratory. POSIX Threads Programming. online at: <https://computing.llnl.gov/tutorials/pthreads/>

[12] The Open Group, 1997 - 1999. What is UNIX? online at: <http://www.unix.org/whitepapers/shdiffs.html>

Extra Links

[1] Ross Johnson. POSIX Threads for Win32. online at: <http://sourceware.org/pthreads-win32/>

[2] Dave McCracken, 2002. IBM Linux Technology Center. POSIX Threads and the Linux Kernel. online at: <http://www.kernel.org/doc/ols/2002/ols2002-pages-330-337.pdf>

[3] L. Blunt Jackson, 2005. NPTL: The New Implementation of Threads for Linux. online at: <http://www.drdobbs.com/open-source/184406204>

[4] Institute of Electrical and Electronics Engineers, Inc, 1998. IEEE POSIX Testing Policy - General Information. online at: <http://standards.ieee.org/regauth/posix/POSIX-A.FM5.pdf>

[5] A Short History of UNIX, 2006. online at: <http://www.unix.com/unix-dummies-questions-answers/7-short-history-unix-l-madden-ic-ac-uk.html>

[6]Bradford Nichols, Dick Buttlar, and Jacqueline Proulx Farrell, O'Reilly & Associates, Inc, 1996. Pthreads Programming. online at: <http://books.google.ca/books?id=EZfElJsWCqgC&pg=PA198&lpg=PA198&dq=kernel+based+pthreads&source=bl&ots=3HFKw_0nqq&sig=P0L9feIb88xJRzQfLd7maKtVnTU&hl=en&ei=Oky3TM-_OaO0nAf1-YiwCA&sa=X&oi=book_result&ct=result&resnum=6&ved=0CCsQ6AEwBQ#v=onepage&q=kernel%20based%20pthreads&f=false>

[7]Bryan O'Sullivan, 1993 - 1996. The History of Threads. online at: <http://www.faqs.org/faqs/os-research/part1/section-10.html>

[8]Lucent Technologies, 2002. The Famous PDP-7 Comes to the Rescue (And Continuous Pages). online at: <http://www.bell-labs.com/history/unix/pdp7.html>

[9]The Linux Information Project, 2004. Pipes: A Brief Introduction. online at: <http://www.linfo.org/pipe.html>