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// SPDX-License-Identifier: EPL-2.0 OR GPL-2.0-or-later
// SPDX-FileCopyrightText: Bradley M. Bell <bradbell@seanet.com>
// SPDX-FileContributor: 2003-24 Bradley M. Bell
// ----------------------------------------------------------------------------
/*
{xrst_begin a11c_pthread.cpp}
{xrst_spell
pthreads
}
A Simple Parallel Pthread Example and Test
##########################################
Purpose
*******
This example just demonstrates pthreads and does not use CppAD at all.
Source Code
***********
{xrst_literal
// BEGIN C++
// END C++
}
{xrst_end a11c_pthread.cpp}
----------------------------------------------------------------------------
*/
// BEGIN C++
# include <pthread.h>
# include <limits>
# include <cmath>
# include <cassert>
// for size_t
# include <cstddef>
# define NUMBER_THREADS 4
# ifdef NDEBUG
# define CHECK_ZERO(expression) expression
# else
# define CHECK_ZERO(expression) assert( expression == 0 );
# endif
namespace {
// Beginning of Example A.1.1.1c of OpenMP 2.5 standard document ---------
void a1(int n, float *a, float *b)
{ int i;
for(i = 1; i < n; i++)
b[i] = (a[i] + a[i-1]) / 2.0f;
return;
}
// End of Example A.1.1.1c of OpenMP 2.5 standard document ---------------
struct start_arg { int n; float* a; float* b; };
void* start_routine(void* arg_vptr)
{ start_arg* arg = static_cast<start_arg*>( arg_vptr );
a1(arg->n, arg->a, arg->b);
void* no_status = nullptr;
pthread_exit(no_status);
return no_status;
}
}
bool a11c(void)
{ bool ok = true;
// Test setup
int i, j, n_total = 10;
float *a = new float[size_t(n_total)];
float *b = new float[size_t(n_total)];
for(i = 0; i < n_total; i++)
a[i] = float(i);
// number of threads
int n_thread = NUMBER_THREADS;
// the threads
pthread_t thread[NUMBER_THREADS];
// arguments to start_routine
struct start_arg arg[NUMBER_THREADS];
// attr
pthread_attr_t attr;
CHECK_ZERO( pthread_attr_init( &attr ) );
CHECK_ZERO( pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE) );
//
// Break the work up into sub work for each thread
int n = n_total / n_thread;
arg[0].n = n;
arg[0].a = a;
arg[0].b = b;
for(j = 1; j < n_thread; j++)
{ arg[j].n = n + 1;
arg[j].a = arg[j-1].a + n - 1;
arg[j].b = arg[j-1].b + n - 1;
if( j == (n_thread - 1) )
arg[j].n = n_total - j * n + 1;
}
for(j = 0; j < n_thread; j++)
{ // inform each thread of which block it is working on
void* arg_vptr = static_cast<void*>( &arg[j] );
CHECK_ZERO( pthread_create(
&thread[j], &attr, start_routine, arg_vptr
) );
}
for(j = 0; j < n_thread; j++)
{ void* no_status = nullptr;
CHECK_ZERO( pthread_join(thread[j], &no_status) );
}
// check the result
float eps = 100.0f * std::numeric_limits<float>::epsilon();
for(i = 1; i < n ; i++)
ok &= std::fabs( (2. * b[i] - a[i] - a[i-1]) / b[i] ) <= eps;
delete [] a;
delete [] b;
return ok;
}
// END C++
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