Example 1 : Memory Consistency Model with respect to flush operations

Download Source code : mem-consistency-openmp3x.c

• Objective

Example program illustrating the memory consistency model provided by OpenMP.

• Description

The program demonstrates how the OpenMP implicit flush (barrier) operation enforces consistency between temporary view and memory. The barrier contains implicit flushes on all threads, as well as thread synchronization. In this example program, at Print 1, the value of x could be either 2 or 5, depending on the timing of the threads, and the implementation of the assignment to x. There are two reasons that the value at Print 1 might not be 5. First, Print 1 might be executed before the assignment to x is executed. Second, even if Print 1 is executed after the assignment, the value 5 is not guaranteed to be seen by thread 1 because a flush may not have been executed by thread 0 since the assignment. The barrier after Print 1 contains implicit flushes on all thread as well as a thread synchronization, so the programmer is guaranteed that the value 5 will be printed by both Print 2 and Print 3.

• Input

None

• Output

Value of the variable x

Example 2 : Program illustrating the use of openmp conditional compilation

Download Source code : mem-cond-compile-openmp3x.c

• Objective

Write an OpenMP program to illustrate the condtional compilation

• Description

The OpenMP implementation supports a preprocessor, macro _OPENMP macro name is used with the OpenMP compilation. To enable conditional compilation, a line with a conditional compilation in fixed sentinel must satisfy the specific criteria. For more details, please refer OpenMP API specification.

• Input

None.

• Output

Print statement will be printed if the macro _OPENMP is defined.

Example 3 : Illustrate how ICVs control the behavior of the OpenMP program.

Download Source code : icv-threads-openmp3x.c

• Objective

Write an OpenMP program to how Internal Control Variables (ICVs) control the behavior of the program

• Description

Demonstrate the use of OpenMP Library calls to change the default values of the internal control variables (ICVs).
The value of the nthreads-var-ICV is changed via a call to omp_set_num_threads for the next parallel region.
The value of the dyn-vars-ICV is changed via a call to omp_set_dynamic() for enable or disable the dynamic adjustment of the number of threads available for the execution of subsequent parallel region.
The value of the nest-vars -ICV is changed via a call to omp_set_nested() to enable or disable the nested parallelism The value of the max_active-levels-var-ICV is changed via a call to omp_set_max_active_levels() to control the the number of nested active parallel regions.

• Input

None

• Output

Values of the ICVs

Example 4 : Illustrate the use of parallel Construct program.

Download Source code : parallel-construct-openmp3x.c

• Objective

OpenMP program to illustrate the use of parallel Construct in coarse-grain parallel program.

• Description

Demonstrate the use of OpenMP pragma parallel Construct for coarse-gain parallelism, i.e each thread in the parallel region decide which part of the global vector to work on based on the thread ID.

• Input

None

• Output

Output Vector after scaling

Example 5 : Illustrate the use of Loop Construct (collapse clause) by a team of threads.

Download Source code : loop-collapse-openmp3x.c

• Objective

OpenMP program to illustrate the use of loop construct using the collapse clause to distribute the loops to all the threads in the team.

• Description

Demonstrate the use of loop construct based on collapse clause. The one or more associated loops will be executed in parallel by threads in the team. The iteration is distributed across all the threads. The loops over multiple indexes (example k or j are collapsed and their iteration space is executed by all threads of the current team.

• Input

None

• Output

time taken to execute the program & value of collapse clause

Example 6 : Illustrate the use of Loop Construct to compute the matrix-vector multiplication

Down load Source code : loop-construct-matvect-openmp3x.c

• Objective

OpenMP program to illustrate the use of loop construct using the collapse clause to distribute the loops to all the threads in the team.

• Description

Demonstrate the use of loop construct based on collapse clause. The one or more associated loops will be executed in parallel by threads in the team. The iteration is distributed across all the threads. The loops over multiple indexes (example k or j are collapsed and their iteration space is executed by all threads of the current team.

• Input

None

• Output

Time taken to execute the program & value of collapse clause

Example 7 : Illustrate the use of task Construct for an recursive algorithm
Download Source code : task-construct-alg-openmp3x.c

• Objective

OpenMP program to illustrate the use of task construct and task wait for recursive algorithm - (Sum of the Fibonacci numbers.)

• Description

In OpenMP program, a task is generated from the code for associated structured block when the thread encounters a task construct. The recursive algorithm (sum of Fibonacci numbers generation) is considered to demonstrate the use of task construct. and task wait. The data environment of the task is created according to data attribute clauses on the task construct.

(The Fibonacci numbers are defined by the following recurrence : Fo = 0, F1 = 1,
F = Fi-1 + Fi-2, for i ≥ 2. Each Fibonacci number is the sum of the two previous numbers.)

• Input

Number of threads to use and the input for recursive algorithm - Fibonacci number generation - range of values )

• Output

Time taken to execute the program & sum of the Fibonacci numbers in the specified range

Example 8 : Illustrate the use of task Construct for an link list traversal.

Download Source code : link-list-alg-openmp3x.c

• Objective

OpenMP program to illustrate the use of task construct for list traversal(irregular parallelism) and analyze the program performance using OpenMP 2.5 pragmas.

• Description

In OpenMP program, a task is generated from the code for associated structured block when the thread encounters a task construct. The link list traversal algorithm generation) is considered to demonstrate the use of task construct. The OpenMP 2.5 pragmas are used to compare the program performance. The data environment of the task is created according to data attribute clauses on the task construct.



• Input

Number of threads to use and the number of nodes in the linked list.)

• Output

Time taken to execute the program &based on OpenMP 2.5 & OpenMP 3.X pragmas.

Example 9 : Illustrate the use of task Construct for in-order tree traverse algorithm.

Download Source code : tree-traverse-alg-openmp3x.c

• Objective

OpenMP program to illustrate the use of task construct for in-order tree traverse algorithm and analyze the program performance using OpenMP 2.5 pragmas.

• Description

The in-order tree traverse algorithm generation) is considered to demonstrate the use of task construct. The OpenMP 2.5 pragmas are used to compare the program performance. The data environment of the task is created according to data attribute clauses on the task construct.

inorderTraverse_Task() : uses OpenMP-3.0 Task Construct. Whenever a thread encounters a task construct, a new explicit task, An explicit task may be executed by any thread in the current team, in parallel with other tasks. In this approach the several task can be executed in parallel.

inorderTraverse_Wtask() : Uses OpenMP-2.5 parallel - section directive. whenever a thread encounter the parallel region it creates the team of threads. When the thread in a team encounter the section directive it execute the section region.



• Input

Number of threads to use and the number of nodes in the tree. )

• Output

Time taken to execute the program &based on OpenMP 2.5 & OpenMP 3.X pragmas.