Below is the current code that I am working with. When I comment out the code to run the progress_bar function, code works perfectly as expected with the mandelbrot printed out into a seperate image file. Yet for whatever reason, when I try to include the function it screeches everything to a halt when the rest of the program has finished up. How do I include the progress_bar function without the program locking into a pseudo-deadlock state? Any and all help is appreciated.
#include <cstdint>
#include <cstdlib>
#include <complex>
#include <fstream>
#include <iostream>
#include <vector>
#include <thread>
#include <mutex>
// Import things we need from the standard library
using std::chrono::duration_cast;
using std::chrono::milliseconds;
using std::complex;
using std::cout;
using std::endl;
using std::ofstream;
// Define the alias "the_clock" for the clock type we're going to use.
typedef std::chrono::steady_clock the_clock;
// The size of the image to generate.
const int WIDTH = 1920;
const int HEIGHT = 1200;
// The number of times to iterate before we assume that a point isn't in the
// Mandelbrot set.
// (You may need to turn this up if you zoom further into the set.)
const int MAX_ITERATIONS = 500;
// The image data.
// Each pixel is represented as 0xRRGGBB.
uint32_t image[HEIGHT][WIDTH];
double progress;
bool progressDone = false;
std::mutex locking;
std::condition_variable conditionMet;
int partsDone = 0;
// Write the image to a TGA file with the given name.
// Format specification: http://www.gamers.org/dEngine/quake3/TGA.txt
void progress_bar() {
std::unique_lock<std::mutex> lock(locking);
while (!progressDone) {
//std::this_thread::sleep_for(std::chrono::nanoseconds(100));
cout << "Current Progress is at: " << progress << "%\n";
conditionMet.wait(lock);
}
cout << "Mandelbrot is finished! Take a look.";
}
void write_tga(const char *filename)
{
ofstream outfile(filename, ofstream::binary);
uint8_t header[18] = {
0, // no image ID
0, // no colour map
2, // uncompressed 24-bit image
0, 0, 0, 0, 0, // empty colour map specification
0, 0, // X origin
0, 0, // Y origin
WIDTH & 0xFF, (WIDTH >> 8) & 0xFF, // width
HEIGHT & 0xFF, (HEIGHT >> 8) & 0xFF, // height
24, // bits per pixel
0, // image descriptor
};
outfile.write((const char *)header, 18);
for (int y = 0; y < HEIGHT; y)
{
for (int x = 0; x < WIDTH; x)
{
uint8_t pixel[3] = {
image[y][x] & 0xFF, // blue channel
(image[y][x] >> 8) & 0xFF, // green channel
(image[y][x] >> 16) & 0xFF, // red channel
};
outfile.write((const char *)pixel, 3);
}
}
outfile.close();
if (!outfile)
{
// An error has occurred at some point since we opened the file.
cout << "Error writing to " << filename << endl;
exit(1);
}
}
// Render the Mandelbrot set into the image array.
// The parameters specify the region on the complex plane to plot.
void compute_mandelbrot(double left, double right, double top, double bottom, double start, double finish)
{
for (int y = start; y < finish; y)
{
for (int x = 0; x < WIDTH; x)
{
// Work out the point in the complex plane that
// corresponds to this pixel in the output image.
complex<double> c(left (x * (right - left) / WIDTH),
top (y * (bottom - top) / HEIGHT));
// Start off z at (0, 0).
complex<double> z(0.0, 0.0);
// Iterate z = z^2 c until z moves more than 2 units
// away from (0, 0), or we've iterated too many times.
int iterations = 0;
while (abs(z) < 2.0 && iterations < MAX_ITERATIONS)
{
z = (z * z) c;
iterations;
}
if (iterations == MAX_ITERATIONS)
{
// z didn't escape from the circle.
// This point is in the Mandelbrot set.
image[y][x] = 0x000000; // black
}
else if (iterations == 0) {
image[y][x] = 0xFFFFFF;
}
else
{
// z escaped within less than MAX_ITERATIONS
// iterations. This point isn't in the set.
image[y][x] = 0xFFFFFF; // white
image[y][x] = 16711680 | iterations << 8 | iterations;
}
std::unique_lock<std::mutex> lock(locking);
progress = double((1.0 / (WIDTH*HEIGHT)) * 100.0);
conditionMet.notify_one();
}
}
partsDone = 1;
}
int main(int argc, char *argv[])
{
cout << "Please wait..." << endl;
// Start timing
std::vector<std::thread*> threads;
the_clock::time_point start = the_clock::now();
std::thread progressive(progress_bar);
for (int slice = 0; slice < 2; slice ) {
// This shows the whole set.
threads.push_back(new std::thread(compute_mandelbrot, -2.0, 1.0, 1.125, -1.125, HEIGHT * (slice / 2), HEIGHT * ((slice 1) / 2)));
// This zooms in on an interesting bit of detail.
//compute_mandelbrot(-0.751085, -0.734975, 0.118378, 0.134488, 0, HEIGHT/16);
}
// Stop timing
for (std::thread* t : threads) {
t->join();
delete t;
}
if (partsDone == 2) {
progressDone = true;
}
progressive.join();
the_clock::time_point end = the_clock::now();
// Compute the difference between the two times in milliseconds
auto time_taken = duration_cast<milliseconds>(end - start).count();
cout << "Computing the Mandelbrot set took " << time_taken << " ms." << endl;
write_tga("output.tga");
std::this_thread::sleep_for(milliseconds(3000));
return 0;
}```
CodePudding user response：
The reason for your non-termination is that no-one notifies the progress bar thread after all the work has finished. Add conditionMet.notify_one(); before the call to progressive.join(). I've ommitted IO to be able to run in an online compiler in the following Demo. Also (as @GoswinvonBrederlow mentions in the comments) make sure to turn partsDone into std::atomic because if >1 threads call partsDone = 1 you'll end up with undefined results and in turn you won't be able to tell if you program is finished.
This would all look simpler if you changed progress to std::atomic and had your progress printer just load the variable in say 100ms intervals (and printed on top of the previous line). Then all you'd need would be the progressDone flag instead of locking and printing for every modification of the progress value. You can see in the following Demo that this runs with zero thread sanitizer warnings. Make sure to adjust the printing interval. This change drops the runtime from ~10.7s to 7s, even though that is just an indication - it's not kosher to time your programs with the thread sanitizer on.