Can't figure out where race condition is occuring
- by Nik
I'm using Valgrind --tool=drd to check my application that uses Boost::thread.
Basically, the application populates a set of "Book" values with "Kehai" values based on inputs through a socket connection.
On a seperate thread, a user can connect and get the books send to them.
Its fairly simple, so i figured using a boost::mutex::scoped_lock on the location that serializes the book and the location that clears out the book data should be suffice to prevent any race conditions. Here is the code:
void Book::clear()
{
boost::mutex::scoped_lock lock(dataMutex);
for(int i =NUM_KEHAI-1; i >= 0; --i)
{
bid[i].clear();
ask[i].clear();
}
}
int Book::copyChangedKehaiToString(char* dst) const
{
boost::mutex::scoped_lock lock(dataMutex);
sprintf(dst, "%-4s%-13s",market.c_str(),meigara.c_str());
int loc = 17;
for(int i = 0; i < Book::NUM_KEHAI; ++i)
{
if(ask[i].changed > 0)
{
sprintf(dst+loc,"A%i%-21s%-21s%-21s%-8s%-4s",i,ask[i].price.c_str(),ask[i].volume.c_str(),ask[i].number.c_str(),ask[i].postTime.c_str(),ask[i].status.c_str());
loc += 77;
}
}
for(int i = 0; i < Book::NUM_KEHAI; ++i)
{
if(bid[i].changed > 0)
{
sprintf(dst+loc,"B%i%-21s%-21s%-21s%-8s%-4s",i,bid[i].price.c_str(),bid[i].volume.c_str(),bid[i].number.c_str(),bid[i].postTime.c_str(),bid[i].status.c_str());
loc += 77;
}
}
return loc;
}
The clear() function and the copyChangedKehaiToString() function are called in the datagetting thread and data sending thread,respectively.
Also, as a note, the class Book:
struct Book
{
private:
Book(const Book&); Book& operator=(const Book&);
public:
static const int NUM_KEHAI=10;
struct Kehai;
friend struct Book::Kehai;
struct Kehai
{
private:
Kehai& operator=(const Kehai&);
public:
std::string price;
std::string volume;
std::string number;
std::string postTime;
std::string status;
int changed;
Kehai();
void copyFrom(const Kehai& other);
Kehai(const Kehai& other);
inline void clear()
{
price.assign("");
volume.assign("");
number.assign("");
postTime.assign("");
status.assign("");
changed = -1;
}
};
std::vector<Kehai> bid;
std::vector<Kehai> ask;
tm recTime;
mutable boost::mutex dataMutex;
Book();
void clear();
int copyChangedKehaiToString(char * dst) const;
};
When using valgrind --tool=drd, i get race condition errors such as the one below:
==26330== Conflicting store by thread 1 at 0x0658fbb0 size 4
==26330== at 0x653AE68: std::string::_M_mutate(unsigned int, unsigned int, unsigned int) (in /usr/lib/libstdc++.so.6.0.8)
==26330== by 0x653AFC9: std::string::_M_replace_safe(unsigned int, unsigned int, char const*, unsigned int) (in /usr/lib/libstdc++.so.6.0.8)
==26330== by 0x653B064: std::string::assign(char const*, unsigned int) (in /usr/lib/libstdc++.so.6.0.8)
==26330== by 0x653B134: std::string::assign(char const*) (in /usr/lib/libstdc++.so.6.0.8)
==26330== by 0x8055D64: Book::Kehai::clear() (Book.h:50)
==26330== by 0x8094A29: Book::clear() (Book.cpp:78)
==26330== by 0x808537E: RealKernel::start() (RealKernel.cpp:86)
==26330== by 0x804D15A: main (main.cpp:164)
==26330== Allocation context: BSS section of /usr/lib/libstdc++.so.6.0.8
==26330== Other segment start (thread 2)
==26330== at 0x400BB59: pthread_mutex_unlock (drd_pthread_intercepts.c:633)
==26330== by 0xC59565: pthread_mutex_unlock (in /lib/libc-2.5.so)
==26330== by 0x805477C: boost::mutex::unlock() (mutex.hpp:56)
==26330== by 0x80547C9: boost::unique_lock<boost::mutex>::~unique_lock() (locks.hpp:340)
==26330== by 0x80949BA: Book::copyChangedKehaiToString(char*) const (Book.cpp:134)
==26330== by 0x80937EE: BookSerializer::serializeBook(Book const&, std::string const&) (BookSerializer.cpp:41)
==26330== by 0x8092D05: BookSnapshotManager::getSnaphotDataList() (BookSnapshotManager.cpp:72)
==26330== by 0x8088179: SnapshotServer::getDataList() (SnapshotServer.cpp:246)
==26330== by 0x808870F: SnapshotServer::run() (SnapshotServer.cpp:183)
==26330== by 0x808BAF5: boost::_mfi::mf0<void, RealThread>::operator()(RealThread*) const (mem_fn_template.hpp:49)
==26330== by 0x808BB4D: void boost::_bi::list1<boost::_bi::value<RealThread*> >::operator()<boost::_mfi::mf0<void, RealThread>, boost::_bi::list0>(boost::_bi::type<void>, boost::_mfi::mf0<void, RealThread>&, boost::_bi::list0&, int) (bind.hpp:253)
==26330== by 0x808BB90: boost::_bi::bind_t<void, boost::_mfi::mf0<void, RealThread>, boost::_bi::list1<boost::_bi::value<RealThread*> > >::operator()() (bind_template.hpp:20)
==26330== Other segment end (thread 2)
==26330== at 0x400B62A: pthread_mutex_lock (drd_pthread_intercepts.c:580)
==26330== by 0xC59535: pthread_mutex_lock (in /lib/libc-2.5.so)
==26330== by 0x80546B8: boost::mutex::lock() (mutex.hpp:51)
==26330== by 0x805473B: boost::unique_lock<boost::mutex>::lock() (locks.hpp:349)
==26330== by 0x8054769: boost::unique_lock<boost::mutex>::unique_lock(boost::mutex&) (locks.hpp:227)
==26330== by 0x8094711: Book::copyChangedKehaiToString(char*) const (Book.cpp:113)
==26330== by 0x80937EE: BookSerializer::serializeBook(Book const&, std::string const&) (BookSerializer.cpp:41)
==26330== by 0x808870F: SnapshotServer::run() (SnapshotServer.cpp:183)
==26330== by 0x808BAF5: boost::_mfi::mf0<void, RealThread>::operator()(RealThread*) const (mem_fn_template.hpp:49)
==26330== by 0x808BB4D: void boost::_bi::list1<boost::_bi::value<RealThread*> >::operator()<boost::_mfi::mf0<void, RealThread>, boost::_bi::list0>(boost::_bi::type<void>, boost::_mfi::mf0<void, RealThread>&, boost::_bi::list0&, int) (bind.hpp:253)
For the life of me, i can't figure out where the race condition is. As far as I can tell, clearing the kehai is done only after having taken the mutex, and the same holds true with copying it to a string.
Does anyone have any ideas what could be causing this, or where I should look?
Thank you kindly.
