Multiprocessing exercise

exercises/multiprocessing/Makefile

+CFLAGS = -Wall -O1 -std=gnu11 #-DNDEBUG
+CFLAGS += -pthread
+LDLIBS = -lm
+
+default: main
+	./$< > out.txt
+
+.PHONEY: clean
+clean:
+	$(RM) main
\ No newline at end of file

exercises/multiprocessing/main.c

+#include<stdio.h>
+#include<stdlib.h>
+#include<pthread.h>
+#include<math.h>
+
+#ifndef NDEBUG
+#define TRACE(args...) fprintf(stderr,args)
+#else
+#define TRACE(...)
+#endif
+
+typedef struct {int points;int* successes;unsigned int* seed;} params;
+
+void* bar(void* arg) {
+	params* p = (params*)arg;
+	for(int i=0;i<(*p).points;i++) {
+		double x = (double)rand_r((*p).seed)/RAND_MAX;
+		double y = (double)rand_r((*p).seed)/RAND_MAX;
+		double dist = sqrt(pow(x,2)+pow(y,2));
+		if(dist<=1) {
+			*((*p).successes)=*((*p).successes)+1;
+		}
+	}
+return NULL;
+}
+
+int main() {
+	int points = (int)5e8;
+	int suc1=0,suc2=0,suc3=0,suc4=0;
+	unsigned int seed1=0,seed2=100,seed3=1000,seed4=2000;
+	params p1 = {points, &suc1, &seed1};
+	params p2 = {points, &suc2, &seed2};
+	params p3 = {points, &suc3, &seed3};
+	params p4 = {points, &suc4, &seed4};
+	
+	pthread_t thread1, thread2, thread3;
+	pthread_attr_t* attributes = NULL;
+	
+	pthread_create(&thread1, attributes, bar, (void*)&p1);
+	pthread_create(&thread2, attributes, bar, (void*)&p2);
+	pthread_create(&thread3, attributes, bar, (void*)&p3);
+	bar((void*)&p4);
+	pthread_join(thread1,NULL);
+	pthread_join(thread2,NULL);
+	pthread_join(thread3,NULL);
+	
+	double pi = (((double)*p1.successes+(double)*p2.successes+(double)*p3.successes+(double)*p4.successes)/(4*points))*4;
+	printf("Estimate of Pi: %g\n",pi);
+return 0;
+}
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exercises/multiprocessing/out.txt

+Estimate of Pi: 3.14159