Boost C++ Libraries: Ticket #4522: allocation problem after grow

status changed; resolution set

Ion Gaztañaga — Sun, 08 Aug 2010 08:02:14 GMT

status new → closed
resolution → invalid

From the help:

"Boost.Interprocess offers off-line segment growing. What does this mean? That the segment can be grown if no process has mapped the managed segment. If the application can find a moment where no process is attached it can grow or shrink to fit the managed segment."

So you must unmap, grow and remap it again:

/* Create SM - Size 100K*/<br>
{
managed_shared_memory shm(create_only, "MySM", 100*1024);
}
//Unmapped here
/* Grow SM By 28K*/
managed_shared_memory::grow("MySM",28*1024);
//Remap it
managed_shared_memory shm(open_only, "MySM");
/* SM full size - 128K*/
int fullSMSize = shm.get_size();
/* SM mem size - 128K - sizeof(SM Header)*/
int memSMSize = shm.get_free_memory();
/* alloc 64K in SM (64K<128K)*/
void* ptr = shm.allocate(64*1024);

Sun, 08 Aug 2010 11:12:26 GMT

Thanks igaztanaga!'''

You are right, in general the growing should be when the SM is unmapped.

Basically, I need shared memory with Fix memory size. But, I don't know the memory size used by Shared Memory mechanism. So, I use grow after using get_free_memory() function.

How can I set in the constructor of the managed_shared_memory the required memory without knowing the SM mechanism size?

Thanks again for your assistance,
Raz

P.S. General question: If the SM based on file I can't call shrink_to_fit() when the SM is mapped, But what about grow?

Mon, 09 Aug 2010 04:13:49 GMT

Thanks igaztanaga!'''

You are right, in general the growing should be when the SM is unmapped.

Basically, I need shared memory with Fix memory size. But, I don't know the memory size used by Shared Memory mechanism. So, I use grow after using get_free_memory() function.

How can I set in the constructor of the managed_shared_memory the required memory without knowing the SM mechanism size?

Thanks again for your assistance,
Raz

P.S.
General question:
If the SM based on file I can't call shrink_to_fit() when the SM is mapped, But what about grow?

Replying to igaztanaga:

From the help:

"Boost.Interprocess offers off-line segment growing. What does this mean? That the segment can be grown if no process has mapped the managed segment. If the application can find a moment where no process is attached it can grow or shrink to fit the managed segment."

So you must unmap, grow and remap it again:
/* Create SM - Size 100K*/<br>
{
managed_shared_memory shm(create_only, "MySM", 100*1024);
}
//Unmapped here
/* Grow SM By 28K*/
managed_shared_memory::grow("MySM",28*1024);
//Remap it
managed_shared_memory shm(open_only, "MySM");
/* SM full size - 128K*/
int fullSMSize = shm.get_size();
/* SM mem size - 128K - sizeof(SM Header)*/
int memSMSize = shm.get_free_memory();
/* alloc 64K in SM (64K<128K)*/
void* ptr = shm.allocate(64*1024);