OpenMP Application Programming Interface Examples

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6.9.5 Nestable Lock Routines
The following example demonstrates how a nestable lock can be used to synchronize updates both
to a whole structure and to one of its members.
C / C++
Example nestable_lock.1.c
S-1 #include
S-2 typedef struct {
S-3 int a,b;
S-4 omp_nest_lock_t lck; } pair;
S-5
S-6 int work1();
S-7 int work2();
S-8 int work3();
S-9 void incr_a(pair *p, int a)
S-10 {
S-11 /* Called only from incr_pair, no need to lock. */
S-12 p->a += a;
S-13 }
S-14 void incr_b(pair *p, int b)
S-15 {
S-16 /* Called both from incr_pair and elsewhere, */
S-17 /* so need a nestable lock. */
S-18
S-19 omp_set_nest_lock(&p->lck);
S-20 p->b += b;
S-21 omp_unset_nest_lock(&p->lck);
S-22 }
S-23 void incr_pair(pair *p, int a, int b)
S-24 {
S-25 omp_set_nest_lock(&p->lck);
S-26 incr_a(p, a);
S-27 incr_b(p, b);
S-28 omp_unset_nest_lock(&p->lck);
S-29 }
S-30 void nestlock(pair *p)
S-31 {
S-32 #pragma omp parallel sections
S-33 {
S-34 #pragma omp section
S-35 incr_pair(p, work1(), work2());
S-36 #pragma omp section
S-37 incr_b(p, work3());
S-38 }
S-39 }
206 OpenMP Examples Version 4.5.0 - November 2016