James Zappia said:
I'm a newbie to C++ and Boost and I'm trying to port a threaded C program I have to Boost.Threads. I'm trying to use scoped_try_lock to test a lock on mutex and it's not working. I'm obviously doing something wrong but I can't figure it out. Below is the source code. Any help would be greatly appreciated.
How is it not working? What do you expect to happen?
What I want to happen is that the main thread keeps trying the lock until it's freed.
SOURCE:
#include <iostream> #include
#include using namespace std;
boost::try_mutex mutex;
void thread_test( void ) { cout << "thread: locking mutex\n";
{ boost::try_mutex::scoped_try_lock lock(mutex); cout << "thread: sleeping for 10 seconds\n"; sleep(10); }
cout << "thread: unlocked mutex - goodbye!\n";
return; }
int main( void ) { cout << "main: creating thread\n"; boost::thread thread(thread_test);
cout << "main: sleeping for 2 seconds\n"; sleep(2);
cout << "main: trying to lock mutex\n"; boost::try_mutex::scoped_try_lock lock(mutex,true);
This will force a lock (which means we'll block until the thread releases the lock).
Change this to: boost::try_mutex::scoped_try_lock lock(mutex, false); This will create your lock object, but not actually lock the mutex. Now the following line will do what you want.
while ( !lock.try_lock() )
Alternatively, you could change the loop (and the constructor again): boost::try_mutex::scoped_try_lock lock(mutex); // does a try_lock while (!lock) { cout << "trying..."; lock.try_lock(); }
Since the above insured the mutex is already locked, this would be a recursive lock which should result in a thread_lock_error exception being thrown. Is this not what's happening for you?
That is what's happening. As stated above, what I would like to happen is the main thread continuously try the lock until it's freed. What am I doing wrong?
I hope this makes sense and you'll understand what you're doing wrong. William E. Kempf