CSC 456 Fall 2013/7a ac

Survey of Primitives for Synchronization

Assignment

7a. Survey of primitives for synchronization Section 7.3 of Solihin covers the need for synchronization at the program level. It mentions lock and unlock operations. But real programs do not usually call lock and unlock mechanisms. Instead, they use higher-level operations, such as Java’s synchronized statement, or Open MP pragmas. Consider popular languages and common OSs such as Linux, MacOS, and Windows. How would programs do synchronization in these environments?

Ideas

synchronization constucts

syncs in clr semaphores in monitors (how many langs available in?)

Different Synchronization Constructs, languages that support them, general info.

Test-and-Set

Test-and-Test-and-Set

Lock-free

Array-lock

Semaphore-Java, C Acquire/Release the semaphore to enter the critical section. Only 1 thread can have the semaphore at a time.

Mutex-Java, C Like a binary semaphore, but with a few differences such as deletion safety (a process holding a mutex cannot be deleted).

Monitor-Java, C

Synchronized-Java

pragma-C (OpenMP)

a study of behavior of synchronization methods in commonly used languages and systems cederman et al.

Types of Synchronization

Locks

A lock is a synchronization mechanism for enforcing limits on access to a resource in an environment where there are many threads of execution. A lock is designed to enforce a mutual exclusion concurrency control policy.<ref name="lock"/> There are several different implementations of locks, as well as higher level constructs that use them, which will be briefly examined below.

Semaphores and Mutexes

Semaphores are simple data types used for controlling access to variables. They classically have two operations, wait() and signal(), sometimes known as acquire() and release(). There are two types of semaphores, binary semaphores and counting semaphores. Binary semaphores can only hold a value of 0 or 1, basically meaning that only one thread can access the semaphore at a time. Counting semaphores can have any number of resource instances. A mutex is essentially a binary semaphore with a few extra safety features that make them more desirable to use than plain semaphores.<ref name="semaphore"/>

Monitors

According to Wikipedia, a monitor is "a thread-safe class, object, or module that uses wrapped mutual exclusion in order to transparently safely be used by more than one thread."<ref name="monitor"/>

Supported Synchronization in Different Languages

The following table shows different programming languages and their support for various synchronization methods. The cells are color coded based on the following key:

Supported Operating Systems Key

None

Windows Only

Mac Only

Linux Only

Windows & Mac

Windows & Linux

Mac & Linux

All

Synchronization Support

Language	Semaphore/Mutex	Monitor	OpenMP	Synchronized	Other
C
Java
C++					Slim Rd/Wr Lock (SRW)
C#
Ruby					Get Sources
Python					Get Sources
PHP					Get Sources
Fortran					Co-Array<ref name="coarray"/>

References

<references> <ref name="monitor">Monitor (synchronization)</ref> <ref name="coarray">Co-Array Fortran</ref> </references>

A Study of the Behavior of Synchronization Methods in Commonly Used Languages and Systems Cederman et al.

Apple Synchronization

C++ Sync Article