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actually do precomputations!
[moebius2.git] / parallel.c
1 /*
2  * Parallel processing
3  */
4
5 #include "common.h"
6
7 #include <pthread.h>
8
9 #include "mgraph.h"
10 #include "parallel.h"
11
12 typedef struct {
13   const struct Vertices *vertices;
14   Computation *separately;
15   void *gendata;
16 } ForAllThreads;
17
18 typedef struct {
19   ForAllThreads *allthreads;
20   int section;
21   void *secdata;
22   pthread_t thread;
23 } PerThread;
24
25 static void *routine(void *thread_v) {
26   PerThread *t= thread_v;
27
28   for (;;) {
29     inparallel_barrier(); /* wait for work to do */
30     ForAllThreads *a= t->allthreads;
31     a->separately(a->vertices, t->section, t->secdata, a->gendata);
32     inparallel_barrier(); /* synchronise for completion */
33   }
34
35   return 0;
36 }
37
38 static int threads_started;
39 static pthread_barrier_t threads_barrier;
40 static PerThread threads[NSECTIONS-1];
41
42 void inparallel(const struct Vertices *vertices,
43                 Computation *separately,
44                 Computation *combine,
45                 size_t secdatasz, void *gendata) {
46   typedef struct { unsigned char secdata[secdatasz]; } SecData;
47
48   ForAllThreads allthreads;
49   SecData secdatas[nsections];
50
51   allthreads.vertices= vertices;
52   allthreads.separately= separately;
53   allthreads.gendata= gendata;
54
55   int s, r;
56
57   if (NSECTIONS>1 && !threads_started) {
58     r= pthread_barrier_init(&threads_barrier, 0, NSECTIONS);
59     if (r) { errno=r; diee("pthread_barrier_init"); }
60
61     for (s=0; s<NSECTIONS-1; s++) {
62       r= pthread_create(&threads[s].thread,0,routine,&threads[s]);
63       if (r) { errno=r; diee("pthread_create"); }
64     }
65     threads_started= 1;
66   }    
67
68   for (s=0; s<NSECTIONS-1; s++) {
69     threads[s].allthreads= &allthreads;
70     threads[s].section= s;
71     threads[s].secdata= secdatas[s].secdata;
72   }
73
74   inparallel_barrier(); /* announce more work to do */
75
76   separately(vertices, NSECTIONS-1, &secdatas[NSECTIONS-1], gendata);
77
78   inparallel_barrier(); /* synchronise for completion */
79
80   for (s=0; s<nsections; s++)
81     combine(vertices, s, &secdatas[s].secdata, gendata);
82 }
83
84 void inparallel_barrier(void) {
85   if (NSECTIONS>1) {
86     int r;
87     r= pthread_barrier_wait(&threads_barrier);
88     if (r && r!=PTHREAD_BARRIER_SERIAL_THREAD)
89       { errno=r; diee("pthread_barrier_wait"); }
90   }
91 }