Why largest threads number runs slower? about perl-html5-dom HOT 13 CLOSED

#include <stdio.h>
#include <stdlib.h>
#include <myhtml/api.h>
#include <sys/time.h>

struct res_html {
	char	*html;
	size_t	size;
};

struct res_html load_html_file(const char* filename)
{
	FILE *fh = fopen(filename, "rb");
	if(fh == NULL) {
		fprintf(stderr, "Can't open html file: %s\n", filename);
		exit(EXIT_FAILURE);
	}
	
	if(fseek(fh, 0L, SEEK_END) != 0) {
		fprintf(stderr, "Can't set position (fseek) in file: %s\n", filename);
		exit(EXIT_FAILURE);
	}
	
	long size = ftell(fh);
	
	if(fseek(fh, 0L, SEEK_SET) != 0) {
		fprintf(stderr, "Can't set position (fseek) in file: %s\n", filename);
		exit(EXIT_FAILURE);
	}
	
	if(size <= 0) {
		fprintf(stderr, "Can't get file size or file is empty: %s\n", filename);
		exit(EXIT_FAILURE);
	}
	
	char *html = (char*)malloc(size + 1);
	if(html == NULL) {
		fprintf(stderr, "Can't allocate mem for html file: %s\n", filename);
		exit(EXIT_FAILURE);
	}
	
	size_t nread = fread(html, 1, size, fh);
	if (nread != size) {
		fprintf(stderr, "could not read %ld bytes (%ld bytes done)\n", size, nread);
		exit(EXIT_FAILURE);
	}
	
	fclose(fh);
	
	struct res_html res = {html, (size_t)size};
	return res;
}

double current_timestamp()
{
	struct timeval t;
	gettimeofday(&t, NULL);
	return (double) t.tv_sec * 1000.0 + (double) t.tv_usec / 1000.0;
}

int main(int argc, const char * argv[])
{
	const char* path;
	
	if (argc == 2) {
		path = argv[1];
	}
	else {
		printf("Bad ARGV!\nUse: print_tree_high_level <path_to_html_file>\n");
		exit(EXIT_FAILURE);
	}
	
	int tries = 20;
	double start, elapsed;
	
	struct res_html res = load_html_file(path);
	
	myhtml_t* myhtml = myhtml_create();
	myhtml_init(myhtml, MyHTML_OPTIONS_PARSE_MODE_SINGLE, 1, 0);
	
	start = current_timestamp();
	
	for (int i = 0; i < tries; ++i) {
		myhtml_tree_t* tree = myhtml_tree_create();
		myhtml_tree_init(tree, myhtml);
		
		myhtml_parse(tree, MyENCODING_UTF_8, res.html, res.size);
		
		myhtml_tree_destroy(tree);
	}
	
	elapsed = current_timestamp() - start;
	
	myhtml_destroy(myhtml);
	
	printf("1 threads: %f\n", elapsed / tries);
	
	myhtml = myhtml_create();
	myhtml_init(myhtml, MyHTML_OPTIONS_DEFAULT, 2, 0);
	
	start = current_timestamp();
	
	for (int i = 0; i < tries; ++i) {
		myhtml_tree_t* tree = myhtml_tree_create();
		myhtml_tree_init(tree, myhtml);
		
		myhtml_parse(tree, MyENCODING_UTF_8, res.html, res.size);
		
		myhtml_tree_destroy(tree);
	}
	
	elapsed = current_timestamp() - start;
	
	myhtml_destroy(myhtml);
	
	printf("2 threads: %f\n", elapsed / tries);
	myhtml = myhtml_create();
	myhtml_init(myhtml, MyHTML_OPTIONS_DEFAULT, 3, 0);
	
	start = current_timestamp();
	
	for (int i = 0; i < tries; ++i) {
		myhtml_tree_t* tree = myhtml_tree_create();
		myhtml_tree_init(tree, myhtml);
		
		myhtml_parse(tree, MyENCODING_UTF_8, res.html, res.size);
		
		myhtml_tree_destroy(tree);
	}
	
	elapsed = current_timestamp() - start;
	
	myhtml_destroy(myhtml);
	
	printf("3 threads: %f\n", elapsed / tries);
	
	return 0;
}