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Programming on Multi-Core Processors Using OpenMP APIs |
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The OpenMP API is used for writing portable multi-threaded applications written in Fortran, C and C++ languages.
The OpenMP programming model plays a key role by providing an easy method for threading applications without burdening
the programmer with the complications of creating, synchronizing load balancing, and destroying threads.
The OpenMP model provides a platform independent set of compiler pragmas, directives, function calls, and environment
variables that explicitly instruct the compiler how and where to use the parallelism in the application.
Example programs using
compiler pragmas, directives, function calls, and environment variables, Compilation and execution
of OpenMP programs, programs numerical and non-numerical computations
are discussed.
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Example 3.1
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OpenMP program : Largest element in a list of numbers using CRITICAL section
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Example 3.2
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OpenMP program : Largest element in a list of numbers using LOCK routines
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Example 3.3
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Write a OpenMP program to find Largest element in a list of numbers using OpenMP REDUCTION clause.
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Example 3.4
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Write OpenMP code to solve Producer-Consumer
problem. (Assignment)
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Example 3.5
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Write OpenMP code to Find k matches in the
list.(Assignment)
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Example 3.6
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Write OpenMP code to Find out minimum in an
unsorted integer array.(Assignment)
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(Source - References :
Books
Multi-threading
OpenMP
-[MCMTh-01], [MCMTh-02], [MCMTh-I03], [MCMTh-05], [MCMTh-09], [MCMTh-11],
[MCMTh-15], [MCMTh-21], [MCBW-44], [MCOMP-01], [MCOMP-02],
[MCOMP-04], [MCOMP-12], [MCOMP-19], [MCOMP-25])
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Description of OpenMP Programs |
Example 3.1 :
Largest element in a list of numbers
using OpenMP CRITICAL section
(Download source code :
omp-maxof-elements-critical.c
/
omp-maxof-elements-critical.f
)
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Objective
Write an OpenMP program to find the largest element in a list
of numbers using OpenMP CRITICAL section.
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Description
Largest element in a list of numbers is found using OpenMP CRITICAL section
and PARALLEL DO loop. Before the CRITICAL section starts the LargeNumber is
examined without any synchronization. If present value of LargeNumber
is already greater than Array(i), then we need proceed no further.
Otherwise Array(i) may be the largest element seen so far, and
we enter the CRITICAL section. Inside the CRITICAL section again
the LargeNumber is examined. This is necessary because previously
examined LargeNumber outside the CRITICAL section so it could
have changed in the meantime. Examining it again within the CRITICAL
section guarantees the thread exclusive access to LargeNumber,
and an update based on the fresh comparison is assured of being
correct. Furthermore, this program will enter the CRITICAL section
only infrequently and benefit from increased parallelism.
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Input
Number of threads and Number of elements of an array .
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Output
Largest element of an array and the time taken to find the Max element of an Array.
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Example 3.2 :
Largest element in a list of numbers using OpenMP Lock routine
(Download source code :
omp-maxof-elements-lock.c
/
omp-maxof-elements-lock.f
)
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Objective
Write an OpenMP program to find the largest element in a list
of numbers using OpenMP Lock routines.
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Description
Lock routines are another mechanism for mutual
exclusion, but provide greater flexibility in their use as
compared to the CRITICAL directives. Firstly, the set/unset
subroutines calls do not have to be block structured. The user
can place these calls at arbitrary points in the program and is
responsible for matching the invocations of the set/unset
routines. Secondly, each lock subroutine takes a lock variable
as an argument. In this example OpenMP Lock routines and
PARALLEL DO
loop is
used.
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Input
Number of threads and Number of elements of an array .
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Output
Largest element of an array and the time taken to find the Max element of an Array.
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Example 3.3 :
Largest element in a list of numbers using OpenMP REDUCTION clause.
(Download source code :
/
omp-maxof-elements-reductionop.f
)
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Objective
Write an OpenMP program to find the largest element in a list
of numbers using OpenMP REDUCTION clause
- Description
Largest element in a list of numbers is found using OpenMP PARALLEL
DO directive and REDUCTION clause. Reductions are a sufficiently
common type of operation. OpenMP includes a reduction data
scope clause just to handle the variable. In reduction, we repeatedly
apply a binary operator to a variable and some other value, and
store the result back in the variable. In this example we have
added the clause REDUCTION ( MAX : LargeNumber), which tells the compiler
that LargeNumber is the target of a sum reduction operation.
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Input
Number of threads and Number of elements of an array .
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Output
Largest element of an array and the time taken to find the Max element of an Array.
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