我是Pthreads和c++的新手，正在尝试并行化图像翻转程序。显然这是行不通的。有人告诉我我需要从Image类中移植一些代码，但不能真正确定移植的含义。我只是复制并粘贴了代码，但我想那是错误的。
我有大致的想法。分配工作量，初始化线程，创建线程，加入线程并定义回调函数。
我不确定cells_per_thread应该是什么。我很确定它应该是图像width * height / threads。看起来正确吗？
使用cmake编译时出现多个错误。
其说法是m_thread_number，getWidth，getHeight，getPixel，temp在范围内未定义。我认为那是因为未移植Image类代码？
PthreadImage.cxx
//Declare a callabck fucntion for Horizontal flip
void* H_flip_callback_function(void* aThreadData);
PthreadImage PthreadImage::flipHorizontally() const
{
if (m_thread_number == 0 || m_thread_number == 1)
{
return PthreadImage(Image::flipHorizontally(), m_thread_number);
}
else
{
PthreadImage temp(getWidth(), getHeight(), m_thread_number);
//Workload allocation
//Create a vector of type ThreadData whcih is constructed at the top of the class under Struct ThreadData. Pass in the number of threads.
vector<ThreadData> p_thread_data(m_thread_number);
//create an integer to hold the last element. inizialize it as -1.
int last_element = -1;
//create an unsigned int to hold how many cells we need per thread. For the image we want the width and height divided by the number of threads.
unsigned int cells_per_thread = getHeight() * getWidth() / m_thread_number;
//Next create a variable to hold the remainder of the sum.
unsigned int remainder = getHeight() * getWidth() % m_thread_number;
//print the number of cells per thread to the console
cout << "Default number for cells per thread: " << cells_per_thread << endl;
//inizialize the threads with a for loop to interate through each thread and populate it
for (int i = 0; i < m_thread_number; i++)
{
//thread ids correspond with the for loop index values.
p_thread_data[i].thread_id = i;
//start is last element + 1 i.e -1 + 1 start = 0.
p_thread_data[i].start_id = ++last_element;
p_thread_data[i].end_id = last_element + cells_per_thread - 1;
p_thread_data[i].input = this;
p_thread_data[i].output = &temp;
//if the remainder is > thats 0 add 1 to the end them remove 1 remainder.
if (remainder > 0)
{
p_thread_data[i].end_id++;
--remainder;
}
//make the last element not = -1 but = the end of the threads.
last_element = p_thread_data[i].end_id;
//print to console what number then thread start and end on
cout << "Thread[" << i << "] starts with " << p_thread_data[i].start_id << " and stops on " << p_thread_data[i].end_id << endl;
}
//create the threads with antoher for loop
for (int i = 0; i < m_thread_number; i++)
{
pthread_create(&p_thread_data[i].thread_id, NULL, H_flip_callback_function, &p_thread_data[i]);
}
//Wait for each thread to complete;
for (int i = 0; i < m_thread_number; i++)
{
pthread_join(p_thread_data[i].thread_id, NULL);
}
return temp;
}
}
回调函数
//Define the callabck fucntion for Horizontal flip
void* H_flip_callback_function(void* aThreadData)
{
//convert void to Thread data
ThreadData* p_thread_data = static_cast<ThreadData*>(aThreadData);
int tempHeight = temp(getHeight());
int tempWidth = temp(getWidth());
for (int i = p_thread_data->start_id; i <= p_thread_data->end_id; i++)
{
// Process every row of the image
for (unsigned int j = 0; j < m_height; ++j)
{
// Process every column of the image
for (unsigned int i = 0; i < m_width / 2; ++i)
{
(*(p_thread_data->output))( i, j) = getPixel(m_width - i - 1, j);
(*(p_thread_data->output))(m_width - i - 1, j) = getPixel( i, j);
}
}
}
}
图像类别
#include <sstream> // Header file for stringstream
#include <fstream> // Header file for filestream
#include <algorithm> // Header file for min/max/fill
#include <numeric> // Header file for accumulate
#include <cmath> // Header file for abs and pow
#include <vector>
#include "Image.h"
//-----------------
Image::Image():
//-----------------
m_width(0),
m_height(0)
//-----------------
{}
//----------------------------------
Image::Image(const Image& anImage):
//----------------------------------
m_width(anImage.m_width),
m_height(anImage.m_height),
m_p_image(anImage.m_p_image)
// ----------------------------------
要移植的图像类代码
//-----------------------------------
Image Image::flipHorizontally() const
//-----------------------------------
{
// Create an image of the right size
Image temp(getWidth(), getHeight());
// Process every row of the image
for (unsigned int j = 0; j < m_height; ++j)
{
// Process every column of the image
for (unsigned int i = 0; i < tempWidth / 2; ++i)
{
temp(i, j) = getPixel(tempWidth - i - 1, j);
temp(tempWidth - i - 1, j) = getPixel(i, j);
}
}
return 0;
}
我感觉它非常接近。任何帮助，不胜感激！
编辑
好，所以这是对任何在此上浪费时间的人的正确代码。
显然有很多错误。
我不知道为什么会有3个for循环。行数应为2。列数应为1。
cells_per_thread应为pixels_per_thread，且应为[[行/线程”，因为@Larry B建议不要ALL每个线程的像素。
setPixel(), getPixel`等。谁知道呢！？struct ThreadData{pthread_t thread_id;unsigned int start_id;unsigned int end_id;const Image *输入；图片*输出；};
正确的回调
void* H_flip_callback_function(void* aThreadData)
{
//convert void to Thread data
ThreadData* p_thread_data = static_cast<ThreadData*>(aThreadData);
int width = p_thread_data->input->getWidth();
// Process every row of the image
for (unsigned int j = p_thread_data->start_id; j <=p_thread_data->end_id; ++j)
}
// Process every column of the image
for (unsigned int i = 0; i < width / 2; ++i)
{
p_thread_data->output->setPixel(i,j, p_thread_data->input->getPixel(width - i - 1, j));
p_thread_data->output->setPixel(width - i - 1, j, p_thread_data->input->getPixel(i, j));
}
}
return 0;
}
所以现在此代码进行编译和翻转。谢谢！
将工作划分为独立的工作单元，您可以将其移交给线程执行。
考虑到这一点，我不同意您对H_flip_callback_function的实现：void* H_flip_callback_function(void* aThreadData)
{
//convert void to Thread data
ThreadData* p_thread_data = static_cast<ThreadData*>(aThreadData);
// Create an image of the right size
PthreadImage temp(getWidth(), getHeight(), m_thread_number);
int tempHeight = temp(getHeight());
int tempWidth = temp(getWidth());
for (int i = p_thread_data->start_id; i <= p_thread_data->end_id; i++)
{
// Process every row of the image
for (unsigned int j = 0; j < tempHeight; ++j)
{
// Process every column of the image
for (unsigned int i = 0; i < tempWidth / 2; ++i)
{
temp(i, j) = getPixel(tempWidth - i - 1, j);
temp(tempWidth - i - 1, j) = getPixel(i, j);
}
}
}
}
从表面上看，您的所有线程看起来都将在整个映像上运行。如果是这种情况，那么单线程和多线程版本之间就没有真正的区别，因为您只是在多线程版本中多次执行相同的工作。。然后，每个线程将翻转分配给它的行，而主线程将收集结果并组装最终图像。关于构建警告和错误，您必须提供完整的源代码，构建设置，环境等。我认为，最小的独立工作单元将是水平翻转图像的单行。但是，如果线程数少于行数，则可以为每个线程分配
（行数/线程数）