Jul 01, 2008 What is TC?? Is this the old Turbo C? If so, then the compiler doesn't support OpenMP. OpenMP requires compiler support. You can find a list of compilers off the OpenMP ARB web page. Currently on the upper left hand side of the page there is box labeled 'What's Here' and under it there is a header 'OpenMP Compilers'. Latest News View Monthly Archives Tweets by OpenMPARB Get all the latest API specifications, technical report drafts and proposals. All the latest books, examples and tutorials to start you on. Feb 23, 2018 openmp parallel for example c omp parallel guided openmp gcc parallel for openmp parallel random number generator omp parallel hello world omp.h parallel openmp parallel if openmp.
-->Provides links to directives used in the OpenMP API.
Visual C++ supports the following OpenMP directives.
For parallel work-sharing:
Directive | Description |
---|---|
parallel | Defines a parallel region, which is code that will be executed by multiple threads in parallel. |
for | Causes the work done in a for loop inside a parallel region to be divided among threads. |
sections | Identifies code sections to be divided among all threads. |
single | Lets you specify that a section of code should be executed on a single thread, not necessarily the master thread. |
For master and synchronization:
Directive | Description |
---|---|
master | Specifies that only the master thread should execute a section of the program. |
critical | Specifies that code is only executed on one thread at a time. |
barrier | Synchronizes all threads in a team; all threads pause at the barrier, until all threads execute the barrier. |
atomic | Specifies that a memory location that will be updated atomically. |
flush | Specifies that all threads have the same view of memory for all shared objects. |
ordered | Specifies that code under a parallelized for loop should be executed like a sequential loop. |
For data environment:
Directive | Description |
---|---|
threadprivate | Specifies that a variable is private to a thread. |
atomic
Specifies that a memory location that will be updated atomically.
Parameters
expression
The statement that has the lvalue, whose memory location you want to protect against more than one write.
The statement that has the lvalue, whose memory location you want to protect against more than one write.
Remarks
The
atomic
directive supports no clauses.For more information, see 2.6.4 atomic construct.
Example
barrier
Synchronizes all threads in a team; all threads pause at the barrier, until all threads execute the barrier.
Remarks
The
barrier
directive supports no clauses.For more information, see 2.6.3 barrier directive.
Example
For a sample of how to use
barrier
, see master.critical
Specifies that code is only be executed on one thread at a time.
Parameters
name
(Optional) A name to identify the critical code. The name must be enclosed in parentheses.
(Optional) A name to identify the critical code. The name must be enclosed in parentheses.
Remarks
The
critical
directive supports no clauses.For more information, see 2.6.2 critical construct.
Example
flush
Specifies that all threads have the same view of memory for all shared objects.
Parameters
var
(Optional) A comma-separated list of variables that represent objects you want to synchronize. If var isn't specified, all memory is flushed.
(Optional) A comma-separated list of variables that represent objects you want to synchronize. If var isn't specified, all memory is flushed.
Remarks
The
flush
directive supports no clauses.For more information, see 2.6.5 flush directive.
Example
for
Causes the work done in a
for
loop inside a parallel region to be divided among threads.Parameters
clauses
(Optional) Zero or more clauses, see the Remarks section.
(Optional) Zero or more clauses, see the Remarks section.
for_statement
A
A
for
loop. Undefined behavior will result if user code in the for
loop changes the index variable.Remarks
The
for
directive supports the following clauses:If
parallel
is also specified, clauses
can be any clause accepted by the parallel
or for
directives, except nowait
.For more information, see 2.4.1 for construct.
Example
master
Specifies that only the master thread should execute a section of the program.
Remarks
The
master
directive supports no clauses.The single directive lets you specify that a section of code should be executed on a single thread, not necessarily the master thread.
For more information, see 2.6.1 master construct.
Example
ordered
Specifies that code under a parallelized
for
loop should be executed like a sequential loop.Openmp C++ Tutorial
Remarks
The
ordered
directive must be within the dynamic extent of a for or parallel for
construct with an ordered
clause.The
ordered
directive supports no clauses.For more information, see 2.6.6 ordered construct.
Example
parallel
Defines a parallel region, which is code that will be executed by multiple threads in parallel.
Parameters
clauses
(Optional) Zero or more clauses, see the Remarks section.
(Optional) Zero or more clauses, see the Remarks section.
Remarks
The
parallel
directive supports the following clauses:parallel
can also be used with the for and sections directives.For more information, see 2.3 parallel construct.
Example
How To Add Openmp In Dev C++
The following sample shows how to set the number of threads and define a parallel region. The number of threads is equal by default to the number of logical processors on the machine. For example, if you have a machine with one physical processor that has hyperthreading enabled, it will have two logical processors and two threads. The order of output can vary on different machines.
sections
Identifies code sections to be divided among all threads.
Parameters
clauses
(Optional) Zero or more clauses, see the Remarks section.
(Optional) Zero or more clauses, see the Remarks section.
Remarks
The
sections
directive can contain zero or more section
directives.The
sections
directive supports the following clauses:If
parallel
is also specified, clauses
can be any clause accepted by the parallel
or sections
directives, except nowait
.For more information, see 2.4.2 sections construct.
Example
single
Lets you specify that a section of code should be executed on a single thread, not necessarily the master thread.
Parameters
clauses
(Optional) Zero or more clauses, see the Remarks section.
(Optional) Zero or more clauses, see the Remarks section.
Remarks
The
single
directive supports the following clauses:The master directive lets you specify that a section of code should be executed only on the master thread.
For more information, see 2.4.3 single construct.
Example
threadprivate
Specifies that a variable is private to a thread.
Parameters
var
A comma-separated list of variables that you want to make private to a thread. var must be either a global- or namespace-scoped variable or a local static variable.
A comma-separated list of variables that you want to make private to a thread. var must be either a global- or namespace-scoped variable or a local static variable.
Remarks
The
threadprivate
directive supports no clauses.The
threadprivate
directive is based on the thread attribute using the __declspec keyword; limits on __declspec(thread)
apply to threadprivate
. For example, a threadprivate
variable will exist in any thread started in the process, not just those threads that are part of a thread team spawned by a parallel region. Be aware of this implementation detail; you may notice that constructors for a threadprivate
user-defined type are called more often then expected.You can use
threadprivate
in a DLL that is statically loaded at process startup, however you can't use threadprivate
in any DLL that will be loaded via LoadLibrary such as DLLs that are loaded with /DELAYLOAD (delay load import), which also uses LoadLibrary
.A
threadprivate
variable of a destructible type isn't guaranteed to have its destructor called. For example:C++ Openmp Example
Users have no control as to when the threads constituting the parallel region will terminate. If those threads exist when the process exits, the threads won't be notified about the process exit, and the destructor won't be called for
threaded_var
on any thread except the one that exits (here, the primary thread). So code shouldn't count on proper destruction of threadprivate
variables.For more information, see 2.7.1 threadprivate directive.
Example
For a sample of using
threadprivate
, see private.