How should I give the class itself to a boost::thread? - c++

Question

I have the following code which raises an error about line m_threads.push_back(boost::thread(boost::ref(*this)));. Could you help me the figure out what is wrong?
#include <algorithm>
#include <fstream> // NOLINT(readability/streams)
#include <string>
#include <utility>
#include <vector>
#include "boost/scoped_ptr.hpp"
#include "boost/thread.hpp"
#include "boost/thread/barrier.hpp"
#include "boost/atomic.hpp"
// #include "gflags/gflags.h"
// #include "glog/logging.h"
// #include "caffe/proto/caffe.pb.h"
// #include "caffe/util/db.hpp"
// #include "caffe/util/io.hpp"
// #include "caffe/util/rng.hpp"
using namespace caffe; // NOLINT(build/namespaces)
using std::pair;
using boost::scoped_ptr;
DEFINE_bool(gray, false,
"When this option is on, treat images as grayscale ones");
DEFINE_bool(shuffle, false,
"Randomly shuffle the order of images and their labels");
DEFINE_int32(threads, 1,
"Build DB using multiple threads.");
DEFINE_string(backend, "lmdb",
"The backend {lmdb, leveldb} for storing the result");
DEFINE_int32(resize_width, 0, "Width images are resized to");
DEFINE_int32(resize_height, 0, "Height images are resized to");
DEFINE_bool(check_size, false,
"When this option is on, check that all the datum have the same size");
DEFINE_bool(encoded, false,
"When this option is on, the encoded image will be save in datum");
DEFINE_string(encode_type, "",
"Optional: What type should we encode the image as ('png','jpg',...).");
class ThreadedReader
{
public:
typedef struct {
int line_id;
bool status;
Datum datum;
} data_entry;
ThreadedReader(int threads, std::vector<std::pair<std::string, int> >& lines,
const string& encode_type, const string& root_folder,
int resize_height, int resize_width, bool is_color) :
m_thread_count(threads), m_lines(lines),
m_barrier_read(threads), m_barrier_fetch(2),
m_id(0), m_thd_done(0),
m_done(false),
m_root_folder(root_folder),
m_encode_type(encode_type),
m_resize_height(resize_height), m_resize_width(resize_width),
m_is_color(is_color)
{
m_data.resize(m_thread_count);
for (int i = 0; i < threads; ++i)
m_threads.push_back(boost::thread(boost::ref(*this)));
}
~ThreadedReader() {
// for (int i = 0; i < m_thread_count; ++i)
// m_threads[i].join();
}
void operator()()
{
for (;;) {
int my_id = m_id.fetch_add(1, boost::memory_order_acq_rel);
const int my_base = my_id % m_thread_count;
m_barrier_read.count_down_and_wait();
m_data[my_base].status = false;
m_data[my_base].line_id = my_id;
if (my_id < m_lines.size()) {
m_data[my_base].line_id = my_id;
m_data[my_base].status = ReadImageToDatum(m_root_folder + m_lines[my_id].first,
m_lines[my_id].second, m_resize_height, m_resize_width, m_is_color,
m_encode_type, &m_data[my_base].datum);
}
if (m_thd_done.fetch_add(1, boost::memory_order_acq_rel) + 1 == m_thread_count) {
m_barrier_fetch.count_down_and_wait();
m_thd_done.store(0, boost::memory_order_release);
if (m_id.load(boost::memory_order_relaxed) >= m_lines.size())
m_done.store(true);
m_barrier_fetch.count_down_and_wait();
}
if (m_id.load(boost::memory_order_relaxed) >= m_lines.size())
break;
}
}
// bool fetch_batch(std::vector<data_entry>& vec)
// {
// using std::swap;
// if (m_done.load(boost::memory_order_acquire))
// return false;
// m_barrier_fetch.count_down_and_wait();
// swap(vec, m_data);
// if (m_data.size() < m_thread_count)
// m_data.resize(m_thread_count);
// m_barrier_fetch.count_down_and_wait();
// return true;
// }
private:
const int m_thread_count;
std::vector<std::pair<std::string, int> >& m_lines;
boost::barrier m_barrier_read;
boost::barrier m_barrier_fetch;
boost::atomic<int> m_id;
boost::atomic<int> m_thd_done;
boost::atomic<bool> m_done;
const std::string& m_root_folder;
const std::string& m_encode_type;
const int m_resize_height, m_resize_width;
const bool m_is_color;
std::vector<data_entry> m_data;
std::vector<boost::thread> m_threads;
};
int main(int argc, char** argv) {
return 0;
}
The errror:
passing ‘const boost::thread’ as ‘this’ argument of ‘boost::thread::operator boost::detail::thread_move_t<boost::thread>()’ discards qualifiers [-fpermissive]
make: *** [.build_release/tools/convert_imageset_threaded.o] Error 1

Answer 1

Your code compiles. It should just be a lot more reduced.
The error message indicates that in your real code you have a const/volatile qualified ThreadedReader, perhaps.
And you shouldn't mix signed/unsigned integers in comparison.
Live On Coliru
// This program converts a set of images to a lmdb/leveldb by storing them
// as Datum proto buffers.
// Usage:
// convert_imageset [FLAGS] ROOTFOLDER/ LISTFILE DB_NAME
//
// where ROOTFOLDER is the root folder that holds all the images, and LISTFILE
// should be a list of files as well as their labels, in the format as
// subfolder1/file1.JPEG 7
// ....
#include <algorithm>
#include <fstream> // NOLINT(readability/streams)
#include <string>
#include <utility>
#include <vector>
#include "boost/scoped_ptr.hpp"
#include "boost/thread.hpp"
#include "boost/thread/barrier.hpp"
#include "boost/atomic.hpp"
// #include "gflags/gflags.h"
// #include "glog/logging.h"
// #include "caffe/proto/caffe.pb.h"
// #include "caffe/util/db.hpp"
// #include "caffe/util/io.hpp"
// #include "caffe/util/rng.hpp"
//using namespace caffe; // NOLINT(build/namespaces)
using std::pair;
using boost::scoped_ptr;
struct Datum {};
class ThreadedReader
{
public:
typedef struct {
int line_id;
bool status;
Datum datum;
} data_entry;
bool ReadImageToDatum(...) { return false; }
ThreadedReader(int threads, std::vector<std::pair<std::string, int> >& lines,
const std::string& encode_type, const std::string& root_folder,
int resize_height, int resize_width, bool is_color) :
m_thread_count(threads), m_lines(lines),
m_barrier_read(threads), m_barrier_fetch(2),
m_id(0), m_thd_done(0),
m_done(false),
m_root_folder(root_folder),
m_encode_type(encode_type),
m_resize_height(resize_height), m_resize_width(resize_width),
m_is_color(is_color)
{
m_data.resize(m_thread_count);
for (int i = 0; i < threads; ++i)
m_threads.push_back(boost::thread(boost::ref(*this)));
}
~ThreadedReader() {
// for (int i = 0; i < m_thread_count; ++i)
// m_threads[i].join();
}
void operator()()
{
for (;;) {
unsigned my_id = m_id.fetch_add(1, boost::memory_order_acq_rel);
const int my_base = my_id % m_thread_count;
m_barrier_read.count_down_and_wait();
m_data[my_base].status = false;
m_data[my_base].line_id = my_id;
if (my_id < m_lines.size()) {
m_data[my_base].line_id = my_id;
m_data[my_base].status = ReadImageToDatum(m_root_folder + m_lines[my_id].first,
m_lines[my_id].second, m_resize_height, m_resize_width, m_is_color,
m_encode_type, &m_data[my_base].datum);
}
if (m_thd_done.fetch_add(1, boost::memory_order_acq_rel) + 1 == m_thread_count) {
m_barrier_fetch.count_down_and_wait();
m_thd_done.store(0, boost::memory_order_release);
if (m_id.load(boost::memory_order_relaxed) >= m_lines.size())
m_done.store(true);
m_barrier_fetch.count_down_and_wait();
}
if (m_id.load(boost::memory_order_relaxed) >= m_lines.size())
break;
}
}
// bool fetch_batch(std::vector<data_entry>& vec)
// {
// using std::swap;
// if (m_done.load(boost::memory_order_acquire))
// return false;
// m_barrier_fetch.count_down_and_wait();
// swap(vec, m_data);
// if (m_data.size() < m_thread_count)
// m_data.resize(m_thread_count);
// m_barrier_fetch.count_down_and_wait();
// return true;
// }
private:
const int m_thread_count;
std::vector<std::pair<std::string, int> >& m_lines;
boost::barrier m_barrier_read;
boost::barrier m_barrier_fetch;
boost::atomic<unsigned> m_id;
boost::atomic<int> m_thd_done;
boost::atomic<bool> m_done;
const std::string& m_root_folder;
const std::string& m_encode_type;
const int m_resize_height, m_resize_width;
const bool m_is_color;
std::vector<data_entry> m_data;
std::vector<boost::thread> m_threads;
};
int main(int argc, char** argv) {
// ::google::InitGoogleLogging(argv[0]);
// #ifndef GFLAGS_GFLAGS_H_
// namespace gflags = google;
// #endif
// gflags::SetUsageMessage("Convert a set of images to the leveldb/lmdb\n"
// "format used as input for Caffe.\n"
// "Usage:\n"
// " convert_imageset [FLAGS] ROOTFOLDER/ LISTFILE DB_NAME\n"
// "The ImageNet dataset for the training demo is at\n"
// " http://www.image-net.org/download-images\n");
// gflags::ParseCommandLineFlags(&argc, &argv, true);
// if (argc < 4) {
// gflags::ShowUsageWithFlagsRestrict(argv[0], "tools/convert_imageset");
// return 1;
// }
// const bool is_color = !FLAGS_gray;
// const int threads = FLAGS_threads > 1 ? FLAGS_threads : 1;
// const bool check_size = FLAGS_check_size;
// const bool encoded = FLAGS_encoded;
// const string encode_type = FLAGS_encode_type;
// std::ifstream infile(argv[2]);
// std::vector<std::pair<std::string, int> > lines;
// std::string filename;
// int label;
// while (infile >> filename >> label) {
// lines.push_back(std::make_pair(filename, label));
// }
// if (FLAGS_shuffle) {
// // randomly shuffle data
// LOG(INFO) << "Shuffling data";
// shuffle(lines.begin(), lines.end());
// }
// LOG(INFO) << "A total of " << lines.size() << " images.";
// if (encode_type.size() && !encoded)
// LOG(INFO) << "encode_type specified, assuming encoded=true.";
// int resize_height = std::max<int>(0, FLAGS_resize_height);
// int resize_width = std::max<int>(0, FLAGS_resize_width);
// // Create new DB
// scoped_ptr<db::DB> db(db::GetDB(FLAGS_backend));
// db->Open(argv[3], db::NEW);
// scoped_ptr<db::Transaction> txn(db->NewTransaction());
// // Storing to db
// std::string root_folder(argv[1]);
// int count = 0;
// const int kMaxKeyLength = 256;
// char key_cstr[kMaxKeyLength];
// int data_size = 0;
// bool data_size_initialized = false;
// if (threads > 1) {
// ThreadedReader rdr(threads, lines, encode_type, root_folder,
// resize_height, resize_width, is_color);
// std::vector<ThreadedReader::data_entry> vec;
// while (rdr.fetch_batch(vec)) {
// for (int i = 0; i < vec.size(); ++i) {
// if (!vec[i].status)
// continue;
// if (check_size) {
// if (!data_size_initialized) {
// data_size = vec[i].datum.channels() * vec[i].datum.height() * vec[i].datum.width();
// data_size_initialized = true;
// } else {
// const std::string& data = vec[i].datum.data();
// CHECK_EQ(data.size(), data_size) << "Incorrect data field size "
// << data.size();
// }
// }
// // sequential
// int length = snprintf(key_cstr, kMaxKeyLength, "%08d_%s", vec[i].line_id,
// lines[vec[i].line_id].first.c_str());
// // Put in db
// string out;
// CHECK(vec[i].datum.SerializeToString(&out));
// txn->Put(string(key_cstr, length), out);
// if (++count % 1000 == 0) {
// // Commit db
// txn->Commit();
// txn.reset(db->NewTransaction());
// LOG(ERROR) << "Processed " << count << " files.";
// }
// }
// }
// } else {
// Datum datum;
// for (int line_id = 0; line_id < lines.size(); ++line_id) {
// bool status;
// std::string enc = encode_type;
// if (encoded && !enc.size()) {
// // Guess the encoding type from the file name
// string fn = lines[line_id].first;
// size_t p = fn.rfind('.');
// if (p == fn.npos)
// LOG(WARNING) << "Failed to guess the encoding of '" << fn << "'";
// enc = fn.substr(p);
// std::transform(enc.begin(), enc.end(), enc.begin(), ::tolower);
// }
// status = ReadImageToDatum(root_folder + lines[line_id].first,
// lines[line_id].second, resize_height, resize_width, is_color,
// enc, &datum);
// if (status == false) continue;
// if (check_size) {
// if (!data_size_initialized) {
// data_size = datum.channels() * datum.height() * datum.width();
// data_size_initialized = true;
// } else {
// const std::string& data = datum.data();
// CHECK_EQ(data.size(), data_size) << "Incorrect data field size "
// << data.size();
// }
// }
// // sequential
// int length = snprintf(key_cstr, kMaxKeyLength, "%08d_%s", line_id,
// lines[line_id].first.c_str());
// // Put in db
// string out;
// CHECK(datum.SerializeToString(&out));
// txn->Put(string(key_cstr, length), out);
// if (++count % 1000 == 0) {
// // Commit db
// txn->Commit();
// txn.reset(db->NewTransaction());
// LOG(ERROR) << "Processed " << count << " files.";
// }
// }
// }
// // write the last batch
// if (count % 1000 != 0) {
// txn->Commit();
// LOG(ERROR) << "Processed " << count << " files.";
// }
return 0;
}