Databases
StackOverflow2013
Postsdbo
POMapViewOfFileEx - valid lpBaseAddress
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POMapViewOfFileEx - valid lpBaseAddress
    primarykey
    data
    text
    <p>In answer to a question about mapping non-contiguous blocks of files into contiguous memory, <a href="https://stackoverflow.com/questions/10454964/mapping-non-contiguous-blocks-from-a-file-into-contiguous-memory-addresses">here</a>, it was suggested by one respondent that I should use <a href="http://msdn.microsoft.com/en-us/library/windows/desktop/aa366887%28v=vs.85%29.aspx" rel="nofollow noreferrer">VirtualAllocEx</a>() with MEM_RESERVE in order to establish a 'safe' value for the final (lpBaseAddress) parameter for <a href="http://msdn.microsoft.com/en-us/library/windows/desktop/aa366763%28v=vs.85%29.aspx" rel="nofollow noreferrer">MapViewOfFileEx</a>().</p> <p>Further investigation revealed that this approach causes MapViewofFileEx() to fail with error 487: "Attempt to access invalid address." <a href="http://msdn.microsoft.com/en-us/library/windows/desktop/aa366887%28v=vs.85%29.aspx" rel="nofollow noreferrer">The MSDN page says</a>:</p> <blockquote> <p>"No other memory allocation can take place in the region that is used for mapping, including the use of the VirtualAlloc or VirtualAllocEx function to reserve memory."</p> </blockquote> <p>While the documentation might be considered ambiguous with respect to valid sequences of calls, experimentation suggests that it is not valid to reserve memory for MapViewOfFileEx() using VirtualAllocEx().</p> <p>On the web, I've found examples with hard-coded values - <a href="http://publib.boulder.ibm.com/infocenter/comphelp/v7v91/index.jsp?topic=/com.ibm.vacpp7a.doc/proguide/ref/xumemex1.htm" rel="nofollow noreferrer">example</a>:</p> <pre><code>#define BASE_MEM (VOID*)0x01000000 </code></pre> <p>...</p> <pre><code>hMap = MapViewOfFileEx( hFile, FILE_MAP_WRITE, 0, 0, 0, BASE_MEM ); </code></pre> <p>To me, this seems inadequate and unreliable... It is far from clear to me why this address is safe, or how many blocks can be safely be mapped there. It seems even more shaky given that I need my solution to work in the context of other allocations... and that I need my source to compile and work in both 32 and 64 bit contexts.</p> <p>What I'd like to know is if there is <strong>any</strong> way to reliably reserve a pool of address space in order that - subsequently - it can be reliably used by MapViewOfFileEx to map blocks to explicit memory addresses.</p>
    singulars
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PTQuestion
    1. USCommunity
    1. USaSteve
    plurals
    1. PL
      singulars
      1. LTLinked
    1. PL
      singulars
      1. LTLinked
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POMapViewOfFileEx - valid lpBaseAddress
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POMapViewOfFileEx - valid lpBaseAddress
      1. USAnthony
      1. VTFavorite
    1. COThere is not. Only thing you can do is do it early.
      singulars
      1. POMapViewOfFileEx - valid lpBaseAddress
      1. USHans Passant
    2. CO@Hans, while I've no reason to disbelieve you, I would welcome a definitive reference stating this. It seems silly to have VirtualAllocEx support for explicit addresses, but no way to reliably reserve address space. Mapping early might work in some contexts, but not for multi-threaded programs where different views need to be mapped during the lifetime of the process.
      singulars
      1. POMapViewOfFileEx - valid lpBaseAddress
      1. USaSteve
    3. COThe definite reference is the MSDN article, understood that you don't like what it says. Clearly you have no hope of mapping a view to a specific address reliably when you cannot control other code that allocates virtual memory. The logical conclusion is thus that you should not try to make it work and leave it up to the OS to pick an address.
      singulars
      1. POMapViewOfFileEx - valid lpBaseAddress
      1. USHans Passant
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload