The only way I could see how to do this was to try to access it and catch the exception that gets thrown if it isn't there.
bool exists()
{
using namespace boost::interprocess;
try
{
managed_shared_memory segment(open_only, kSharedMemorySegmentName);
return segment.check_sanity();
}
catch (const std::exception &ex) {
std::cout << "managed_shared_memory ex: " << ex.what();
}
return false;
}
Is there a better way?
I was playing around with boost::interprocess and happened to ask the same question. I did a little digging before finally settling on open_or_create for my needs. However, deep in the bowels of the template spaghetti that is boost (mine is 1.62), we find this gem:
/*<... snip ...>*/
//This loop is very ugly, but brute force is sometimes better
//than diplomacy. If someone knows how to open or create a
//file and know if we have really created it or just open it
//drop me a e-mail!
bool completed = false;
spin_wait swait;
while(!completed){
try{
create_device<FileBased>(dev, id, size, perm, file_like_t());
created = true;
completed = true;
}
catch(interprocess_exception &ex){
if(ex.get_error_code() != already_exists_error){
throw;
}
else{
try{
DeviceAbstraction tmp(open_only, id, read_write);
dev.swap(tmp);
created = false;
completed = true;
}
catch(interprocess_exception &e){
if(e.get_error_code() != not_found_error){
throw;
}
}
catch(...){
throw;
}
}
}
catch(...){
throw;
}
swait.yield();
}
/* <... snip ...> */
The above is from managed_open_or_create_impl.hpp at about line 360, in the priv_open_or_create() method. Seems the answer is no. No, there's no good way to check whether a shared memory has been created prior to trying to opening it.
If you are working with shared_memory_objects:
using namespace boost::interprocess;
bool exists()
{
try
{
shared_memory_object shm_source(open_only, map_shared_memory_name.c_str(), read_only);
std::string name = shm_source.get_name();
return (!name.empty());
}
catch (const std::exception &ex)
{
return (false);
}
}
