Re: [Boost-bugs] [Boost C++ Libraries] #4522: allocation problem after grow

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #4522: allocation problem after grow
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2010-08-09 04:13:49

#4522: allocation problem after grow
-------------------------------+--------------------------------------------
  Reporter:  razzik@…          |       Owner:  igaztanaga                                    
      Type:  Bugs              |      Status:  closed                                        
 Milestone:  Boost 1.44.0      |   Component:  interprocess                                  
   Version:  Boost 1.43.0      |    Severity:  Showstopper                                   
Resolution:  invalid           |    Keywords:  interprocess shared_memory ipc grow allocation
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Comment (by Raz M <razzik@…>):

 '''Thanks igaztanaga!!'''[[br]]

 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,[[br]]Raz

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

 Replying to [comment:1 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:
 >
 > {{{#!c++
 > /* 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);
 > }}}

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/4522#comment:3>
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