Re: incorrect checksum for freed object
On 8/18/2010 10:19 AM, Philipp Kraus wrote:
On 2010-08-18 15:53:49 +0200, Victor Bazarov said:
On 8/18/2010 8:37 AM, Philipp Kraus wrote:
I'm to create a multithreaded algorithm and I get this runtime error
message:
incorrect checksum for freed object - object was probably modified after
being freed
[...]
With one thread everything works fine, on more threads I'll get the
error message. I understand this correctly, that the message says that
several threads on another object to access and modify data there?
The statement after the last 'that' is supposed to be complete. Let's
try to use it as a separate sentence:
"Several threads on another object to access and modify data there"
"Several threads" is the subject.
"Another object" is the object (with "on" as the preposition).
Where is the verb? Several threads WHAT on another object?
Sorry I'm a little bit confused
Well, English can be confusing, but so can be German. And Russian.
Here everything is pretty straightforward. You just need to complete
the sentence. "Several threads" DO SOMETHING "on another object". What
do the threads do? Converge? Dance? Feed? Concentrate? Work? For
example,
I understand this correctly, that the message says that several
threads /urinate/ on another object to access and modify data there?
(I am not sure about the question mark after that statement either)
I would like to understand the message in that way, that I can solve my
problem
If you pass some object by reference to any threads, make sure that
the object *survives* while there is at least one thread using it. The
best approach is the reference counting. Increment the counter just
before a thread begins using the object. When the thread is done using
that object, *the thread* must decrement the reference counter. When
the counter goes to zero, the object should delete itself.
Here a code excerpt:
std::vector< worker<T,D> > l_worker;
boost::thread_group l_threadgroup;
for(std::size_t i=0; i < p_threads; ++i) {
l_worker.push_back( worker<T,D>(p_iteration, p_stepsize, m_fulltable,
m_derivation, m_optimize, m_static, p_batch) );
l_threadgroup.create_thread( boost::bind( &worker<T,D>::optimize,
l_worker[i] ) );
}
My worker objects get parameters, which are only read in ::optimize. I
don't change the data in the parameter objects (or changes the iterator
the object?). If I copy the reference by the copy-constructor or
std::copy to a new object in my worker / thread object, I wouldn't get
the error message? My thread object throws the error message on
different runs with a different number of messages, but the numer is
less than thread count.
The code excerpt does not contain anything that would indicate the cause
of your problem. So, two things. Your problem is not of the language
nature, it's of the Boost usage nature. As such it seems to me
off-topic here. Consider asking in Boost online forums or in
'comp.programming.threads'. And, the error message you get is from the
run-time environment. It is not from the compiler or linker. The
run-time environment belongs to your OS, and you might find it more
productive to ask about your OS in the newsgroup dedicated to your OS.
Best of luck!
V
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