I have a program which reads 2 input files. First file contains some random words which are put into an BST and AVL tree. Then the program looks for the words listed in the second read file and says if they exist in the trees, then writes an output file with the information gathered. While doing this the program prints out the time spent for finding a certain item. However the program does not seem to be measuring the time spent.
BST* b = new BST();
AVLTree* t = new AVLTree();
string s;
ifstream in;
in.open(argv[1]);
while(!in.eof())
{
in >> s;
b->insert(s);
t->insert(s);
}
ifstream q;
q.open(argv[2]);
ofstream out;
out.open(argv[3]);
int bstItem = 0;
int avlItem = 0;
float diff1 = 0;
float diff2 = 0;
clock_t t1, t1e, t2, t2e;
while(!q.eof())
{
q >> s;
t1 = clock();
bstItem = b->findItem(s);
t1e = clock();
diff1 = (float)(t1e - t1)/CLOCKS_PER_SEC;
t2 = clock();
avlItem = t->findItem(s);
t2e = clock();
diff2 = (float)(t2e - t2)/CLOCKS_PER_SEC;
if(avlItem == 0 && bstItem == 0)
cout << "Query " << s << " not found in " << diff1 << " microseconds in BST, " << diff2 << " microseconds in AVL" << endl;
else
cout << "Query " << s << " found in " << diff1 << " microseconds in BST, " << diff2 << " microseconds in AVL" << endl;
out << bstItem << " " << avlItem << " " << s << "\n";
}
The clock() value I get just before entering while and just after finishing it is exactly the same. So it appears as if the program does not even run the while loop at all, so it print 0. I know that this is not the case since it takes around 10 seconds for the program the finish as it should. Also the output file contains correct results, so the possibility of having bad findItem() functions is also not true.
I did a little bit research in Stack Overflow, and saw that many people experience the same problem as me. However none of the answers I read solved it.
I solved my problem using a higher resolution clock, though the clock resolution was not my problem. I used clock_gettime() from time.h. As far as I know higher clock resolutions than clock() is platform dependent and this particular method I used in my code is only available for Linux. I still haven't figured out why I wasn't able to obtain healthy results from clock(), but I suspect platform dependency again.
An important note, the use of clock_gettime() requires you to include POSIX real time extension when compiling the code.
So you should do:
g++ a.cpp b.cpp c.cpp -lrt -o myProg
where -lrt is the parameter to include POSIX extensions.
If (t1e - t1) is < CLOCKS_PER_SEC your result will always be 0 because integer division is truncated. Cast CLOCKS_PER_SEC to float.
diff1 = (t1e - t1)/((float)CLOCKS_PER_SEC);
Related
I have a code written in C++ in Visual Studio:
auto start = std::chrono::high_resolution_clock::now();
result = function(-1, 1, 9999999);
auto end = std::chrono::high_resolution_clock::now();
double time_taken = chrono::duration_cast<chrono::microseconds>(end - start).count();
time_taken *= 1e-6;
std::cout << "result: " << result << "time : " << fixed << time_taken << setprecision(6) << " sec" << endl;
The problem is: I run the code in Release mode and time_taken always equals 0. When I switch to the Debug mode time_taken is between 1 and 2 seconds. I tried different ways to pinpoint time but time_taken always equals 0. How can I fix this?
Thanks in advance for your help!
Apparently you are lacking clock resolution. Or the function was partly or fully optimized away.
Generally it is not trivial to profile small functions.
One thing you should do is to call it a lot of times, and measure time of whole run, then divide this time by number of calls.
Also make sure the function is actually fully computed at runtime by stroing result in a volatile variable, and taking input from volatile variables.
Why is the timestamp of time(0) at multiple places in a C++ program the same value?
Ex:
int main(){
cout << time(0) << endl;
cout << time(0) << endl;
cout << time(0) << endl;
cout << time(0) << endl;
}
All of the values above are the same. Is this because the program is executed at such a fast speed that the time values in the above example are all the same?
Could someone help me out? Thanks!
The resolution of the time() function isn't fine grained enough to result in different values to make a different result for each call you make, i.e. the CPU is faster.
You might try to insert std::this_thread::sleep_for calls to check what timing resolution fits for your needs with the hardware and OS you have at hand.
The time(0) function returns the current time in seconds.
The code that you upload will run all the code in one second.
Therefore, even if the time is output, all the same time is output.
The following code is to output the current time continuously for 3 seconds.
If you run it, you will see a lot of numbers, but if you look closely you can see that the number changes three times.
#include <iostream>
#include <ctime>
int main()
{
time_t s = std::time(0); // time_t is int64 in windows 10 64bit.
time_t n;
do {
n = std::time(0);
std::cout << n << " ";
} while ((s + 3) > n); // repeat until 3 sec passed.
return 0;
}
I am writing an in-depth test program for a data structure I had to write for a class. I am trying to time how long it takes functions to execute and store them in an array for later printing. To double check that it was working I decided to print it immediately, and I found out it is not working.
Here is the code where I get the times and store them in an array that is in a struct.
void test1(ArrayLinkedBag<ItemType> &bag,TestAnalytics &analytics){
clock_t totalStart;
clock_t incrementalStart;
clock_t stop; //Both timers stop at the same time;
// Start TEST 1
totalStart = clock();
bag.debugPrint();
cout << "Bag Should Be Empty, Checking..." << endl;
incrementalStart = clock();
checkEmpty<ItemType>(bag);
stop = clock();
analytics.test1Times[0] = analytics.addTimes(incrementalStart,stop);
analytics.test1Times[1] = analytics.addTimes(totalStart,stop);
cout << analytics.test1Times[0] << setprecision(5) << "ms" << endl;
std::cout << "Time: "<< setprecision(5) << (stop - totalStart) / (double)(CLOCKS_PER_SEC / 1000) << " ms" << std::endl;
cout << "===========================================" << endl; //So I can find the line easier
}
Here is the code where I am doing the calculation that I am putting in the array, this function is located in a TestAnalytics struct
double addTimes(double start, double stop){
return (stop - start)/ (double)(CLOCKS_PER_SEC/1000);
}
Here is a snippet of the output I am getting:
Current Head: -1
Current Size: 0
Cell: 1, Index: 0, Item: 6317568, Next Index: -2
Cell: 2, Index: 1, Item: 4098, Next Index: -2
Cell: 3, Index: 2, Item: 6317544, Next Index: -2
Cell: 4, Index: 3, Item: -683175280, Next Index: -2
Cell: 5, Index: 4, Item: 4201274, Next Index: -2
Cell: 6, Index: 5, Item: 6317536, Next Index: -2
Bag Should Be Empty, Checking...
The Bag Is Empty
0ms
Time: 0 ms
===========================================
I am trying to calculate the time as per a different post on this site.
I am using clang compiler on an UNIX system. Is it possible that the number is still too small to show above 0?
Unless you're stuck with an old (pre-C++ 11) compiler/library, I'd use the functions from the <chrono> header:
template <class ItemType>
void test1(ArrayLinkedBag<ItemType> &bag){
using namespace std::chrono;
auto start = high_resolution_clock::now();
bag.debugPrint();
auto first = high_resolution_clock::now();
checkEmpty(bag);
auto stop = high_resolution_clock::now();
std::cout << " first time: " << duration_cast<microseconds>(first - start).count() << " us\n";
std::cout << "second time: " << duration_cast<microseconds>(stop - start).count() << " us\n";
}
Some parts are a bit verbose (to put it nicely) but it still works reasonably well. duration_cast supports difference types down to (at least) nanoseconds, which is typically sufficient for timing even relatively small/fast pieces of code (though it's not guaranteed that it uses a timer with nanosecond precision).
In addition to Jerry's good answer (which I've upvoted), I wanted to add just a little more information that might be helpful.
For timing I recommend steady_clock over high_resolution_clock because steady_clock is guaranteed to not be adjusted (especially backwards) during your timing. Now on Visual Studio and clang, this can't possibly happen because high_resolution_clock and steady_clock are exactly the same type. However if you're using gcc, high_resolution_clock is the same type as system_clock, which is subject to being adjusted at any time (say by an NTP correction).
But if you use steady_clock, then on every platform you have a stop-watch-like timer: Not good for telling you the time of day, but not subject to being corrected at an inopportune moment.
Also, if you use my free, open-source, header-only <chrono> extension library, it can stream out durations in a much more friendly manner, without having to use duration_cast nor .count(). It will print out the duration units right along with the value.
Finally, if you call steady_clock::now() multiple times in a row (with nothing in between), and print out that difference, then you can get a feel for how precisely your implementation is able to time things. Can it time something as short as femtoseconds? Probably not. Is it as coarse as milliseconds? We hope not.
Putting this all together, the following program was compiled like this:
clang++ test.cpp -std=c++14 -O3 -I../date/include
The program:
#include "date/date.h"
#include <iostream>
int
main()
{
using namespace std::chrono;
using date::operator<<;
for (int i = 0; i < 100; ++i)
{
auto t0 = steady_clock::now();
auto t1 = steady_clock::now();
auto t2 = steady_clock::now();
auto t3 = steady_clock::now();
auto t4 = steady_clock::now();
auto t5 = steady_clock::now();
auto t6 = steady_clock::now();
std::cout << t1-t0 << '\n';
std::cout << t2-t1 << '\n';
std::cout << t3-t2 << '\n';
std::cout << t4-t3 << '\n';
std::cout << t5-t4 << '\n';
std::cout << t6-t5 << '\n';
}
}
And output for me on macOS:
150ns
80ns
69ns
53ns
63ns
64ns
88ns
54ns
66ns
66ns
59ns
56ns
59ns
69ns
76ns
74ns
73ns
73ns
64ns
60ns
58ns
...
I'm trying to figure out how to time the execution of part of my program, but when I use the following code, all I ever get back is 0. I know that can't be right. The code I'm timing recursively implements mergesort of a large array of ints. How do I get the time it takes to execute the program in milliseconds?
//opening input file and storing contents into array
index = inputFileFunction(inputArray);
clock_t time = clock();//start the clock
//this is what needs to be timed
newRecursive.mergeSort(inputArray, 0, index - 1);
//getting the difference
time = clock() - time;
double ms = double(time) / CLOCKS_PER_SEC * 1000;
std::cout << "\nTime took to execute: " << std::setprecision(9) << ms << std::endl;
You can use the chrono library in C++11. Here's how you can modify your code:
#include <chrono>
//...
auto start = std::chrono::steady_clock::now();
// do whatever you're timing
auto end = std::chrono::steady_clock::now();
auto durationMS = std::chrono::duration_cast<std::chrono::microseconds>(end - start);
std::cout << "\n Time took " << durationMS.count() << " ms" << std::endl;
If you're developing on OSX, this blog post from Apple may be useful. It contains code snippets that should give you the timing resolution you need.
I am trying to measure my code performance (which is the execution of an OpenCL kernel) and I really need to understand the speed-up. I tried to use clock() and clock_gettime() functions.
In first case my code is simple and straightforward, and it is measured correctly:
struct timespec start_r, start_m, stop_r, stop_m;
double realtime, monotonic;
time_t start2 = clock();
if(clock_gettime(CLOCK_REALTIME, &start_r) == -1) {
cout << "clock realtime error!" << endl;
}
if(clock_gettime(CLOCK_MONOTONIC, &start_m) == -1) {
cout << "clock realtime error!" << endl;
}
double res = 0.0;
for(unsigned long i = 0; i < total; i++) {
res += data[i];
}
cout << "res = " << res << endl;
time_t end2 = clock();
if(clock_gettime(CLOCK_REALTIME, &stop_r) == -1) {
cout << "clock realtime error!" << endl;
}
if(clock_gettime(CLOCK_MONOTONIC, &stop_m) == -1) {
cout << "clock realtime error!" << endl;
}
cout << "Time clock() = " << (end2 - start2)/(double)CLOCKS_PER_SEC << endl;
realtime = (stop_r.tv_sec - start_r.tv_sec) + (double)(stop_r.tv_nsec - start_r.tv_nsec) / (double)BILLION;
monotonic = (stop_m.tv_sec - start_m.tv_sec) + (double)(stop_m.tv_nsec - start_m.tv_nsec) / (double)BILLION;
cout << "Realtime = " << realtime << endl << "Monotonic = " << monotonic << endl;
It gives understandable results - all three results are nearly the same.
When it comes to measuring the execution time of an OpenCL kernel, I do exactly the same, but The results I get are awful:
Time = 0.04
Realtime = 0.26113
Monotonic = 0.26113
Can you give me any idea of what is wrong with it?
If it is a usual problem of measuring OpenCL kernel performance, can you suggest the best way to measure it? Thanks!
If you have access to a C++11 compiler consider using std::chrono instead: http://en.cppreference.com/w/cpp/chrono
There are three clock types built into the new C++ standard:
std::steady_clock
std::system_clock
std::high_resolution_clock
Furthermore the library is well-designed to handle different levels of granularity, whether you want microsecond accuracy, or something else. For software I have written in the past (large industrial engineering-type simulations) I've relied on std::steady_clock for doing all of my timings with no complaints :-).
The function clock will in some systems measure the CPU time used by the application. If your application uses OpenCL, it will probably spend most of its time waiting for the actual calculation to be performed by the graphics card, so clock will not give you "the real time it took to get the result". It's similar to using clock when reading data from a file, for example - the time it takes to read 100MB from a file is perhaps 2 seconds. But only 0.01s of CPU time is needed to send the commands to the hard disk and collect the data back when it has been stored in memory by the hard disk controller. So the clock gives "0.01s", not "2s".