how to manage reading a global string from a thread?
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1
I working in a simple program that reads from std input and prints the buffer when a socket message arrives.
std::string data;
void listen_for_messages();
int main(int argc, char *argv)
{
std::thread listenMessages(listen_for_messages);
char c;
while(cin.get(c)) {
data += c;
}
}
void listen_for_messages()
{
while(1) {
//receive a message from the socket
std::cout << "r>" << data << std::endl;
}
}
but data is always empty and I don't know why. Please help me!
I'm using g++ (Ubuntu 7.3.0-16ubuntu3) 7.3.0 compiler and following compile command:
g++ -o myprogram -pthread myprogram.cpp
c++
edited Nov 16 '18 at 15:11
NathanOliver
98.5k16138218
asked Nov 16 '18 at 15:08
ibadoibado
1144
add a comment |
1
I working in a simple program that reads from std input and prints the buffer when a socket message arrives.
std::string data;
void listen_for_messages();
int main(int argc, char *argv)
{
std::thread listenMessages(listen_for_messages);
char c;
while(cin.get(c)) {
data += c;
}
}
void listen_for_messages()
{
while(1) {
//receive a message from the socket
std::cout << "r>" << data << std::endl;
}
}
but data is always empty and I don't know why. Please help me!
I'm using g++ (Ubuntu 7.3.0-16ubuntu3) 7.3.0 compiler and following compile command:
g++ -o myprogram -pthread myprogram.cpp
c++
edited Nov 16 '18 at 15:11
NathanOliver
98.5k16138218
asked Nov 16 '18 at 15:08
ibadoibado
1144
Hint:std::mutex
– NathanOliver
Nov 16 '18 at 15:10
You have no synchronisation ondata, so the compiler probably assumes it cannot possibly ever change inlisten_for_messages, and optimises the print to an empty string. Just a guess, but you definitely have the synchronisation bug.
– BoBTFish
Nov 16 '18 at 15:10
I think mutex doesn't really help in this case. I no need synchronization, since one thread write the string and other read it. Is there a way to say the compiler that my string is maybe acces by different threads?
– ibado
Nov 16 '18 at 18:19
add a comment |
1
1
1
I working in a simple program that reads from std input and prints the buffer when a socket message arrives.
std::string data;
void listen_for_messages();
int main(int argc, char *argv)
{
std::thread listenMessages(listen_for_messages);
char c;
while(cin.get(c)) {
data += c;
}
}
void listen_for_messages()
{
while(1) {
//receive a message from the socket
std::cout << "r>" << data << std::endl;
}
}
but data is always empty and I don't know why. Please help me!
I'm using g++ (Ubuntu 7.3.0-16ubuntu3) 7.3.0 compiler and following compile command:
g++ -o myprogram -pthread myprogram.cpp
c++
edited Nov 16 '18 at 15:11
NathanOliver
98.5k16138218
asked Nov 16 '18 at 15:08
ibadoibado
1144
I working in a simple program that reads from std input and prints the buffer when a socket message arrives.
std::string data;
void listen_for_messages();
int main(int argc, char *argv)
{
std::thread listenMessages(listen_for_messages);
char c;
while(cin.get(c)) {
data += c;
}
}
void listen_for_messages()
{
while(1) {
//receive a message from the socket
std::cout << "r>" << data << std::endl;
}
}
but data is always empty and I don't know why. Please help me!
I'm using g++ (Ubuntu 7.3.0-16ubuntu3) 7.3.0 compiler and following compile command:
g++ -o myprogram -pthread myprogram.cpp
c++
c++
edited Nov 16 '18 at 15:11
NathanOliver
98.5k16138218
asked Nov 16 '18 at 15:08
ibadoibado
1144
edited Nov 16 '18 at 15:11
NathanOliver
98.5k16138218
asked Nov 16 '18 at 15:08
ibadoibado
1144
edited Nov 16 '18 at 15:11
NathanOliver
98.5k16138218
edited Nov 16 '18 at 15:11
NathanOliver
98.5k16138218
edited Nov 16 '18 at 15:11
NathanOliver
98.5k16138218
98.5k16138218
asked Nov 16 '18 at 15:08
ibadoibado
1144
asked Nov 16 '18 at 15:08
ibadoibado
1144
asked Nov 16 '18 at 15:08
ibadoibado
1144
1144
Hint:std::mutex
– NathanOliver
Nov 16 '18 at 15:10
You have no synchronisation ondata, so the compiler probably assumes it cannot possibly ever change inlisten_for_messages, and optimises the print to an empty string. Just a guess, but you definitely have the synchronisation bug.
– BoBTFish
Nov 16 '18 at 15:10
I think mutex doesn't really help in this case. I no need synchronization, since one thread write the string and other read it. Is there a way to say the compiler that my string is maybe acces by different threads?
– ibado
Nov 16 '18 at 18:19
add a comment |
Hint:std::mutex
– NathanOliver
Nov 16 '18 at 15:10
You have no synchronisation ondata, so the compiler probably assumes it cannot possibly ever change inlisten_for_messages, and optimises the print to an empty string. Just a guess, but you definitely have the synchronisation bug.
– BoBTFish
Nov 16 '18 at 15:10
I think mutex doesn't really help in this case. I no need synchronization, since one thread write the string and other read it. Is there a way to say the compiler that my string is maybe acces by different threads?
– ibado
Nov 16 '18 at 18:19
Hint:
std::mutex– NathanOliver
Nov 16 '18 at 15:10
Hint:
std::mutex– NathanOliver
Nov 16 '18 at 15:10
You have no synchronisation on
data, so the compiler probably assumes it cannot possibly ever change in listen_for_messages, and optimises the print to an empty string. Just a guess, but you definitely have the synchronisation bug.– BoBTFish
Nov 16 '18 at 15:10
You have no synchronisation on
data, so the compiler probably assumes it cannot possibly ever change in listen_for_messages, and optimises the print to an empty string. Just a guess, but you definitely have the synchronisation bug.– BoBTFish
Nov 16 '18 at 15:10
I think mutex doesn't really help in this case. I no need synchronization, since one thread write the string and other read it. Is there a way to say the compiler that my string is maybe acces by different threads?
– ibado
Nov 16 '18 at 18:19
I think mutex doesn't really help in this case. I no need synchronization, since one thread write the string and other read it. Is there a way to say the compiler that my string is maybe acces by different threads?
– ibado
Nov 16 '18 at 18:19
add a comment |
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Hint:
std::mutex– NathanOliver
Nov 16 '18 at 15:10
You have no synchronisation on
data, so the compiler probably assumes it cannot possibly ever change inlisten_for_messages, and optimises the print to an empty string. Just a guess, but you definitely have the synchronisation bug.– BoBTFish
Nov 16 '18 at 15:10
I think mutex doesn't really help in this case. I no need synchronization, since one thread write the string and other read it. Is there a way to say the compiler that my string is maybe acces by different threads?
– ibado
Nov 16 '18 at 18:19