• The Old New Thing

    Speeding up adding items to a combobox or listbox

    • 33 Comments

    Just a little tip: If you're going to be adding a lot of items to a listbox or combobox, there are a few little things you can do to improve the performance significantly. (Note: The improvements work only if you have a lot of items, like hundreds. Of course, the usability of a listbox with a hundred items is questionable, but I'm assuming you have a really good reason for doing this.)

    First, you can disable redraw while you add the items. (This tip works for all controls, actually.)

      SetWindowRedraw(hwnd, FALSE);
      ... add the items ...
      SetWindowRedraw(hwnd, TRUE);
      InvalidateRect(hwnd, NULL, TRUE);
    

    SetWindowRedraw is defined in the <windowsx.h> header file.

    This suppresses the control redrawing itself each time you add an item. But there is still something else you can do:

      SendMessage(hwndCombo, CB_INITSTORAGE, cItems, cbStrings);
      ... add the items ...
    

    (For listbox controls, use the LB_INITSTORAGE message.)

    cItems is the number of items you intend to add, and cbStrings is the total amount of memory (in bytes) required by the strings you intend to add.

    It's okay if these values are merely estimates. If you are too low, then there will still be some reallocation for the extra items. If you are too high, then some memory will be allocated but remain unused.

    Some people will recommend using LockWindowUpdate, but this is wrong. LockWindowUpdate disables drawing in the window you specify, but suppressing flickering during updates is not what it was designed for.

    One clear limitation limitation of LockWindowUpdate is that only one window can be locked for update at a time. So if two windows each try the LockWindowUpdate trick at the same time, only one of them will succeed. That's not particularly reliable, now, is it.

    The purpose of LockWindowUpdate is to assist code that is drawing drag/drop feedback. If you are drawing the cursor for a drag/drop operation, you don't want the window beneath the cursor to start drawing (and thereby overwrite your beautiful cursor). So you lock the window while you draw the cursor and unlock it when the cursor leaves the window.

    That's why there is only one locked window at a time: There can be only one drag/drop operation active at a time, since there is only one mouse.

  • The Old New Thing

    Did you know that Baltimore has a Rumor Control Center?

    • 11 Comments

    A little-known department in the city of Baltimore is the Rumor Control Center, whose purpose is to squash rumors before they get out of hand.

    Scott Simon talked with supervisor Tom Saunders on cash rewards for blue-eyed cicadas and other rumors he's had to handle in the past.

  • The Old New Thing

    What are these directories called 0409 and 1033?

    • 34 Comments

    A reader asked,

    I was wondering why it's common for some Microsoft products to have a directory called "1033" within it's program directory installation location? What does it mean?

    This reader was probably from the United States, because 1033 is the locale identifier for "English (United States)", whose hexadecimal value is 0x0409. You may also find directories called "0409". Some programs use hex codes and some use decimal. Go figure.

    Here is a list of a whole bunch of locales and their identification numbers, both in decimal and hexadecimal. Now you too can become an expert in locale identifiers.

    The value of a locale identifier is given by the formula

    primary language + 1024 * sub-language

    For example, Swiss German is LANG_GERMAN + 1024 * SUBLANG_GERMAN_SWISS = 7 + 1024 * 2 = 2055.

    So why would a program create a directory named after a language code?

    Many Microsoft products support a multilingual user interface. This means that the same program can be used to display its user interface in multiple languages. Office and Windows are the two biggest examples. Language-specific resources need to be broken out into their own directories so they won't conflict with resources corresponding to some other language.

    (For fun, I installed the Swedish language pack on my computer at work, so all strings - including the error messages - are in Swedish.)

  • The Old New Thing

    Calculate the speed of light by microwaving marshmallows

    • 4 Comments

    A simple experiment, and you can eat the results!

    Via The Annals of Improbable Research.

  • The Old New Thing

    Let there be a grand clubhouse feast!

    • 3 Comments

    Kenny Mayne is one of the regular anchors for ESPN SportsCenter and for some reason I find this particular home run call hilarious:

    I am king of the diamond! Let there be a grand clubhouse feast! [WAV] Bring me the finest meats and cheeses throughout the land!
    — From The SportsCenter Altar multimedia download center.

    Here's a whimisical interview where he explains where he got that from [RealAudio].

    Another one I like for its understatedness:

    <Football player> has decided to tackle people on behalf of the <NFL team>. Terms of the contract are not disclosed, but we believe it has something to do with money.

    Actually, I enjoyed just reading through a collection of phrases used by the SportsCenter anchors.

    Almost makes me want to watch television.

  • The Old New Thing

    When can a thread receive window messages?

    • 16 Comments

    Everybody who has messed with window messaging knows that GetMessage and PeekMessage retrieve queued messages, which are dispatched to windows via DispatchMessage.

    Most people also know that GetMessage and PeekMessage will also dispatch nonqueued messages. (All pending nonqueued messages are dispatched, then the first queued message is returned.)

    But apparently not many people realize that SendMessage will also dispatch messages!

    If one thread T1 send a message to a window that belongs to another thread T2, the sending thread T1 is put to sleep until the receiving thread replies to the message. But if somebody else sends a message to thread T1, thread T1 is woken to process the message, then is returned to sleep.

    Why is that?

    Well, when two threads T1 and T2 are working together, it's common that thread T1 may send a message to thread T2, and while handling the message, thread T2 will send messages back to thread T1 before it returns to T1. Therefore, thread T1 must be ready to accept incoming sent messages.

    For example, thread T1 may send a message saying, "Tell me about all the X's that you know." Thread T2 will then send one message back to thread T1 saying, "Here's an X", and then another message to say "Here's another X", and so on, until it has finished telling thread T1 about all the X's, at which point it returns.

    Thread T1 now knows, when the original message returns, that it has received the entire list of X's from thread 2.

    This back-and-forth is how DDE service discovery works.

    Another case is that thread T1 sends a message to thread T2, and thread T2 needs to ask thread T1 for help before it can finish the operation. This isn't as strange as it sounds. You do something similar all the time without realizing it when you respond to a WM_NOTIFY message by sending messages back to the control that sent the notification. (For example, you may respond to a LVN_ITEMACTIVATE by sending back a LVM_GETITEM to get information about the item that was activated.)

    So remember: Any time you send a message, there is a potential for re-entrancy.

  • The Old New Thing

    Deleted but not yet forgotten

    • 18 Comments

    Earlier, I discussed the interactions of the various FILE_SHARE_* flags, then Larry Osterman took this as inspiration to give a history of the file sharing flags.

    If a file is opened with delete-sharing enabled and you delete the file, the file doesn't actually go away until the open handles are closed. In the meantime, the file hangs around as a zombie. (Under Unix, a deleted file with open handles is removed from the directory and merely floats around in the happy sea of inodes with no name.)

    Why doesn't the file go away?

    Well, one reason is that device drivers can ask for the name of the file that corresponds to an open handle. If the directory entry were removed, then there would be no name to return! (What would you expect to be returned from GetModuleFileName if the module no longer exists? Should it be possible for GetModuleFileName to return ERROR_FILE_NOT_FOUND?)

    Another reason is that if power were to be lost while a "forgotten but not lost" handle was still open, you would now have lost clusters on the disk.

    And a final reason is that a "pending delete" file isn't actually gone for good. A driver can "undelete" the file by clearing the delete-on-close flag!

  • The Old New Thing

    The suburbs make you fat, more researchers conclude

    • 12 Comments

    Two legs good - four wheels bad. (With apologies to George Orwell.)

    Researchers link increase car use with obesity.

    Each hour spent in a car was associated with a 6 percent increase in the likelihood of obesity and each half-mile walked per day reduced those odds by nearly 5 percent, the researchers found.

    A study last year came to a similar conclusion. Good to know that quality research yields quality results.

  • The Old New Thing

    Do not underestimate the power of the game Deer Hunter

    • 35 Comments

    During the run-up to Windows XP Service Pack 2 Beta in December of last year, there was a list of five bugs that the release management team decided were so critical that they were going to slip the beta until those bugs got fixed.

    The third bug on the list: Deer Hunter 4 won't run.

    Deer Hunter has the power to stop a beta.

  • The Old New Thing

    An easy way to determine whether you have a particular file permission

    • 21 Comments

    Sometimes you might want to determine whether you can do something without actually doing it. For example, you might want to know whether you have a particular permission in a directory, say permission to delete files from it.

    One way is to retrieve the ACL and then check whether the current user has the desired permission. The AccessCheck function does most of the heavy lifting there.

    Or you can realize, "Hey, wait a second, there is an entire security infrastructure whose job it is to decide who can access which files. Why not use it?"

    For example, here's how you can check whether the user has permission to delete files from a directory:

    BOOL CanDeleteFilesFromDirectory(LPCTSTR pszPath)
    {
      HANDLE h = CreateFile(pszPath, FILE_DELETE_CHILD, FILE_SHARE_READ |
                            FILE_SHARE_WRITE | FILE_SHARE_DELETE, NULL,
                            OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, NULL);
      if (h != INVALID_HANDLE_VALUE) {
        CloseHandle(h);
      }
      return h != INVALID_HANDLE_VALUE;
    }
    

    What we did was open the directory (which requires backup semantics) and ask for FILE_DELETE_CHILD access. If it succeeded, then we have permission to delete files from it. [Corrected 7:52am]

    Note, of course, that this information is purely advisory. You shouldn't be making security decisions based on this, because the permissions might change between the time you check and the time you try.

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