Compound Files...
P. Senthil -- senthilp@geocities.com
Tuesday, November 26, 1996
Environment: VC++ 1.52, Win 95
1. I'm writing a program which uses compound files for storage. The file
itself has only one stream and a root storage. Since the program is on a
multiuser env. I have to open the storage in SHARE_DENY_WRITE mode. The
other flags are READ_WRITE and DIRECT for the first time and if open
fails READ and DIRECT. This is a valid combination according to the OLE
2.0 documentation. But, StgOpenStorage is returning
INVALID_FLAGCOMBINATION everytime.
I've checked up Brockschmidt and Kruglinski but all samples they have
open the root storage only as SHARE_EXCLUSIVE.
2. This problem is with MFC. If I have a document class derived from
COleDocument, the default behaviour for File|Open is: it opens the
compound file in SHARE_EXCLUSIVE. How can I modify this behaviour
without overriding the entire File|Open process...
Thanks in advance for any help in this matter...
--
P. Senthil
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Slh1995@aol.com
Tuesday, November 26, 1996
[Mini-digest: 2 responses]
In a message dated 96-11-26 19:13:26 EST, P. Senthil writes:
<< Environment: VC++ 1.52, Win 95
1. I'm writing a program which uses compound files for storage. The file
itself has only one stream and a root storage. Since the program is on a
multiuser env. I have to open the storage in SHARE_DENY_WRITE mode. The
other flags are READ_WRITE and DIRECT for the first time and if open
fails READ and DIRECT. This is a valid combination according to the OLE
2.0 documentation. But, StgOpenStorage is returning
INVALID_FLAGCOMBINATION everytime.
I've checked up Brockschmidt and Kruglinski but all samples they have
open the root storage only as SHARE_EXCLUSIVE.
2. This problem is with MFC. If I have a document class derived from
COleDocument, the default behaviour for File|Open is: it opens the
compound file in SHARE_EXCLUSIVE. How can I modify this behaviour
without overriding the entire File|Open process...
Thanks in advance for any help in this matter...
--
P. Senthil
Mail: senthilp@geocities.com
>>
For problem #1, I've used the following code:
IO_RETURN_TYPE CMediamstDoc::DoOpenDocument( CString& sPathName )
{
HRESULT hr;
const char* pszPathName = sPathName;
CString sErrorString = sPathName;
CString sTemp; sErrorString += " : ";
ASSERT( pszPathName == NULL || AfxIsValidString( pszPathName ) );
BeginWaitCursor( );
DeleteContents( );
TRY
{
m_lpRootStg = NULL; // always start new root storage
LPSTORAGE lpStorage;
DWORD flag = STGM_READ | STGM_TRANSACTED | STGM_SHARE_DENY_WRITE;
#ifdef WIN32
USES_CONVERSION;
hr = ::StgOpenStorage( T2COLE(pszPathName), NULL, flag, 0, 0,
&lpStorage );
#else
hr = ::StgOpenStorage( pszPathName, NULL, flag, 0, 0, &lpStorage );
#endif // WIN32
if ( hr != NOERROR )
{
AfxThrowOleException(hr);
}
ASSERT(lpStorage != NULL);
m_lpRootStg = lpStorage;
LoadFromStorage( );
SetModifiedFlag( FALSE ); // start off with unmodified
}
CATCH( COleException, e )
{
...
return IO_OTHER_ERROR;
}
END_CATCH
EndWaitCursor( );
return IO_NO_ERROR;
}
However, after some fairly extensive network testing, it turns out that the
above code still causes hangups in a network environment. If the file
resides on a Novell server, everything is ok, but if you are running a
Windows NT server, then only one client may access your document at a time.
This may because of the 2nd problem you mention (inside MFC), which I have
not yet found a workaround to.
-Steve Haber
www.mindq.com
-----From: Alexander Walsh
Ha ... what timing ... I just posted a similiar article.
Here's what we did. Basically we copied the code from
COleDocument::OnOpenDocument() and did it ourselves ... with the
following trick. When the first user opens the file, we grant read/write
access to them, all subsequent users opening the file get read-only.
We keep a flag around in the document to indicate this. The users are
notified of the new state. They can still save their file, but need to
rename it.
We are still testing it, but it seems to work on all platforms. What a
stupid limitation and the MFC part of the stuff wasn't engineered to
allow alterations. Oh well.
Stay tuned,
Sandy
--
----
Alexander (Sandy) Walsh | I hope I die peacefully in my sleep
Project Lead - GQL Reports | like my Dad ... and not screaming
Andyne Computing Ltd | hysterically like his passengers.
David Shillito -- David_Shillito@msn.com
Monday, December 02, 1996
In a message dated 96-11-26 19:13:26 EST, P. Senthil writes:
<< Environment: VC++ 1.52, Win 95
1. I'm writing a program which uses compound files for storage. The file
itself has only one stream and a root storage. Since the program is on a
multiuser env. I have to open the storage in SHARE_DENY_WRITE mode. The
other flags are READ_WRITE and DIRECT for the first time and if open
fails READ and DIRECT. This is a valid combination according to the OLE
2.0 documentation. But, StgOpenStorage is returning
INVALID_FLAGCOMBINATION everytime.
I've checked up Brockschmidt and Kruglinski but all samples they have
open the root storage only as SHARE_EXCLUSIVE.
2. This problem is with MFC. If I have a document class derived from
COleDocument, the default behaviour for File|Open is: it opens the
compound file in SHARE_EXCLUSIVE. How can I modify this behaviour
without overriding the entire File|Open process...
Thanks in advance for any help in this matter...
--
P. Senthil
Mail: senthilp@geocities.com
>>
We found we did, indeed, need to modify the entire File|Open process.
We needed to override both COleDocument::OnOpenDocument and
COleDocument::OnSaveDocument. Since these are 2 or 3 levels deep in the
inheritance hierarchy this meant cloning methods from their callers too such
as
COleLinkingDoc::OnOpenDocument and COleServerDoc::OnOpenDocument.
Our documents are partially read into memory but continue to be accessed
as the user wanders through them. When the user saves the entire document
is written out again.
When a user opens a document we give him STGM_DIRECT |STGM_READ |
STGM_SHARE_DENY_WRITE access. This allows multiple users to have a
document open simultaneously. When a users saves we write to a temporary
storage,
copying, if necessary, from the storage of the still open document. When the
temp
storage is completed we close it and close the original. We then attempt to
delete
the original and rename the temp storage. This will fail if we were not the
only reader.
The user can then choose to save under a different name or get the other
readers to
close their copies of the document befirre retrying his save operation.
David Shillito
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