feat: add parallelism to get 1B lognormal samples in 11s.

examples/more/11_billion_lognormals_paralell/example.c

@@ -0,0 +1,30 @@
+#include "../../../squiggle.h"
+#include "../../../squiggle_more.h"
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+// Estimate functions
+int main()
+{
+    // set randomness seed
+    // uint64_t* seed = malloc(sizeof(uint64_t));
+    // *seed = 1000; // xorshift can't start with 0
+    // ^ not necessary, because parallel_sampler takes care of the seed.
+
+    int n_samples = 1000 * 1000 * 1000;
+    int n_threads = 16;
+    double sampler(uint64_t* seed){
+        return sample_lognormal(0, 10, seed);
+    }
+    double* results = malloc(n_samples * sizeof(double));
+
+    parallel_sampler(sampler, results, n_threads, n_samples);
+    double avg = array_sum(results, n_samples)/n_samples;
+    printf("Average of 1B lognormal(0,10): %f", avg);
+
+    free(results);
+
+    // free(seed);
+    // ^ not necessary, because parallel_sampler takes care of the seed.
+}