Exceptions while using mutex and condition_variable

Question

I'm writing a program to read data from .txt file and using it in output .txt file. I'm using two threads; The first thread is for reading the data from the .txt file, and the second one is for writing it in the output file. I'm a beginner in the programming with mutex and condition_variable and for somehow my program handles exceptions... The exception is

abort() has been called.

These are the two threads methods:

void MessagesSender::readsData() { ifstream data; data.open("data.txt"); string buffer; bool toEmpty = false; std::unique_lock<mutex> locker(mtx, std::defer_lock); if (data.is_open()) { while (std::getline(data, buffer)) //reads line to the buffer. { locker.lock(); this->messages.push(buffer); //push the message to the queue. locker.unlock(); cond.notify_one(); } data.close(); toEmpty = true; } else { cout << "Error opening file... " << endl; } if (toEmpty) //empty the data file. { ofstream emptyFile; emptyFile.open("data.txt", ofstream::out | ofstream::trunc); emptyFile.close(); } } void MessagesSender::sendsData() { ofstream output; output.open("output.txt"); string tempString; string tempMessage; if (output.is_open()) { std::unique_lock<mutex> locker(mtx, std::defer_lock); locker.lock(); cond.wait(locker); while (!(this->messages.empty())) { tempMessage = this->messages.front(); this->messages.pop(); locker.unlock(); for (std::vector<string>::iterator it = this->userNames.begin(); it != this->userNames.end(); ++it) { tempString = *it; tempString += ": "; tempString += tempMessage; tempString += "\n"; output << tempString; } } output.close(); } else { cout << "Error opening file... " << endl; } }

Why is the program handling exception?

"abort() has been called" is not an exception. If an exception was thrown and not caught, you got a more detailed message that includes the type of the exception. — Pete Becker
– Pete Becker, Commented Jan 24, 2018 at 20:48
@FrançoisAndrieux I can't because the work with the threads is very unstable... — I.Klein
– I.Klein, Commented Jan 24, 2018 at 20:48
@I.Klein "because the work with the threads is very unstable" Huh?? — user9212993
– user9212993, Commented Jan 24, 2018 at 20:50
@I.Klein I don't understand what you mean. Most debuggers will be able to break on abort, providing you with a nice call stack. — François Andrieux
– François Andrieux, Commented Jan 24, 2018 at 20:51

Mike van Dyke · Accepted Answer · 2018-01-24 20:55:49Z

One possible error is that you are repeatedly unlocking the mutex in your while-loop, even though the mutex is not locked:

if (output.is_open()) { std::unique_lock<mutex> locker(mtx, std::defer_lock); locker.lock(); cond.wait(locker); while (!(this->messages.empty())) { tempMessage = this->messages.front(); this->messages.pop(); // if multiple messages are in the queue, you unlock multiple times // even though the mutex is not locked locker.unlock(); for (std::vector<string>::iterator it = this->userNames.begin(); it != this->userNames.end(); ++it) { tempString = *it; tempString += ": "; tempString += tempMessage; tempString += "\n"; output << tempString; } } output.close(); }

According to unique_lock::unlock this throws a std::system_error

Collectives™ on Stack Overflow

Exceptions while using mutex and condition_variable

1 Answer 1

Comments

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Related