LOCK-FREE DINING PHILOSOPHER

The past few years have marked the start of a historic transition from sequential to parallel computation. The necessity to write parallel programs is increasing as systems are getting more complex while processor speed increases are slowing down. Current parallel programming uses low-level programming constructs like threads and explicit synchronization using locks to coordinate thread execution. Parallel programs written with these constructs are difficult to design, program and debug. Also locks have many drawbacks which make them a suboptimal solution. One such drawback is that locks should be only used to enclose the critical section of the parallel-processing code. If locks are used to enclose the entire code then the performance of the code drastically decreases. Software Transactional Memory (STM) is a promising new approach to programming shared-memory parallel processors. It is a concurrency control mechanism that is widely considered to be easier to use by programmers than locking. It allows portions of a program to execute in isolation, without regard to other, concurrently executing tasks. A programmer can reason about the correctness of code within a transaction and need not worry about complex interactions with other, concurrently executing parts of the program. If STM is used to enclose the entire code then the performance of the code is the same as that of the code in which STM is used to enclose the critical section only and is far better than code in which locks have been used to enclose the entire code. So STM is easier to use than locks as critical section does not need to be identified in case of STM. This paper shows the concept of writing code using Software Transactional Memory (STM) and the performance comparison of codes using locks with those using STM. It also shows why the use of STM in parallel-processing code is better than the use of locks.

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STM: Lock-Free Synchronization

International Journal of Computer and Communication Technology ◽

10.47893/ijcct.2014.1245 ◽

2014 ◽

pp. 206-212

Author(s):

Ryan Saptarshi Ray

Keyword(s):

Parallel Programming ◽

Shared Memory ◽

Concurrency Control ◽

Control Mechanism ◽

Parallel Processors ◽

Software Transactional Memory ◽

New Approach ◽

Low Level ◽

Complex Interactions ◽

Design Program

Current parallel programming uses low-level programming constructs like threads and explicit synchronization (for example, locks, semaphores and monitors) to coordinate thread execution which makes these programs difficult to design, program and debug. In this paper we present Software Transactional Memory (STM) which is a promising new approach for programming in parallel processors having shared memory. It is a concurrency control mechanism that is widely considered to be easier to use by programmers than other mechanisms such as locking. It allows portions of a program to execute in isolation, without regard to other, concurrently executing tasks. A programmer can reason about the correctness of code within a transaction and need not worry about complex interactions with other, concurrently executing parts of the program.

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FROM LOCKS TO CORRECT AND EFFICIENT TRANSACTIONAL MEMORY

Journal of Circuits System and Computers ◽

10.1142/s0218126612400051 ◽

2012 ◽

Vol 21 (02) ◽

pp. 1240005

Author(s):

CHENG WANG ◽

YOUFENG WU

Keyword(s):

Transactional Memory ◽

Parallel Programs ◽

Parallel Program ◽

Program Execution ◽

Software Transactional Memory ◽

Correctness Condition ◽

Critical Sections ◽

Efficient Software

Transactional memory addresses a number of important issues in lock-based parallel programs. Unfortunately, the semantics of transactions are different from those of critical sections defined by locks. The semantic differences make it difficult to correctly port existing lock-based programs to transaction-based programs. Experienced programmers accustomed to lock-based programming can easily make mistakes in transaction-based programming as parallel programs running correctly using locks can run incorrectly when critical sections are converted to using transactions. This problem becomes even more severe in porting lock-based programs to use the efficient software transactional memory. In this paper, we first identify three necessary properties in a program for the program execution using transactions to be equivalent to the program execution using locks. Assuming that the input lock-based program satisfies the necessary properties (i.e., a well-behaved parallel program), we next present a correctness condition to verify the transactional memory implementation in order for the program execution using transactions to be equivalent to the program execution using locks. Finally, we develop a correct and efficient software transactional memory implementation that satisfies the correctness condition so that locks in the well-behaved parallel programs can be converted to use the efficient software transactional memory easily and correctly.

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