Taken from WinAPI guide:
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Priority Boosts
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Each thread has a dynamic priority. This is the priority the scheduler uses to determine which thread to execute. Initially, a thread's dynamic priority is the same as its base priority. The system can boost and lower the dynamic priority, to ensure that it is responsive and that no threads are starved for processor time. The system does not boost the priority of threads with a base priority level between 16 and 31. Only threads with a base priority between 0 and 15 receive dynamic priority boosts.
The system boosts the dynamic priority of a thread to enhance its responsiveness as follows.
· When a process that uses NORMAL_PRIORITY_CLASS is brought to the foreground, the scheduler boosts the priority class of the process associated with the foreground window, so that it is greater than or equal to the priority class of any background processes. The priority class returns to its original setting when the process is no longer in the foreground.
· When a window receives input, such as timer messages, mouse messages, or keyboard input, the scheduler boosts the priority of the thread that owns the window.
· When the wait conditions for a blocked thread are satisfied, the scheduler boosts the priority of the thread. For example, when a wait operation associated with disk or keyboard I/O finishes, the thread receives a priority boost.
After raising a thread's dynamic priority, the scheduler reduces that priority by one level each time the thread completes a time slice, until the thread drops back to its base priority. A thread's dynamic priority is never less than its base priority.
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ShellExecute Function Call
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The ShellExecute function opens or prints a specified file. The file can be an executable file or a document file.
HINSTANCE ShellExecute(
HWND hwnd, // handle to parent window
LPCTSTR lpOperation, // pointer to string that specifies operation to perform
LPCTSTR lpFile, // pointer to filename or folder name string
LPCTSTR lpParameters, // pointer to string that specifies executable-file parameters
LPCTSTR lpDirectory, // pointer to string that specifies default directory
INT nShowCmd // whether file is shown when opened
);
Parameters
hwnd
Specifies a parent window. This window receives any message boxes that an application produces. For example, an application may report an error by producing a message box.
lpOperation
Pointer to a null-terminated string that specifies the operation to perform. The following operation strings are valid:
String Meaning
"open" The function opens the file specified by lpFile. The file can be an executable file or a document file. The file can be a folder to open.
"print" The function prints the file specified by lpFile. The file should be a document file. If the file is an executable file, the function opens the file, as if "open" had been specified.
"explore" The function explores the folder specified by lpFile.
The lpOperation parameter can be NULL. In that case, the function opens the file specified by lpFile.
lpFile
Pointer to a null-terminated string that specifies the file to open or print or the folder to open or explore. The function can open an executable file or a document file. The function can print a document file.
lpParameters
If lpFile specifies an executable file, lpParameters is a pointer to a null-terminated string that specifies parameters to be passed to the application.
If lpFile specifies a document file, lpParameters should be NULL.
lpDirectory
Pointer to a null-terminated string that specifies the default directory.
nShowCmd
If lpFile specifies an executable file, nShowCmd specifies how the application is to be shown when it is opened. This parameter can be one of the following values:
Value Meaning
SW_HIDE Hides the window and activates another window.
SW_MAXIMIZE Maximizes the specified window.
SW_MINIMIZE Minimizes the specified window and activates the next top-level window in the Z order.
SW_RESTORE Activates and displays the window. If the window is minimized or maximized, Windows restores it to its original size and position. An application should specify this flag when restoring a minimized window.
SW_SHOW Activates the window and displays it in its current size and position.
SW_SHOWDEFAULT Sets the show state based on the SW_ flag specified in the STARTUPINFO structure passed to the CreateProcess function by the program that started the application. An application should call ShowWindow with this flag to set the initial show state of its main window.
SW_SHOWMAXIMIZED Activates the window and displays it as a maximized window.
SW_SHOWMINIMIZED Activates the window and displays it as a minimized window.
SW_SHOWMINNOACTIVE Displays the window as a minimized window. The active window remains active.
SW_SHOWNA Displays the window in its current state. The active window remains active.
SW_SHOWNOACTIVATE Displays a window in its most recent size and position. The active window remains active.
SW_SHOWNORMAL Activates and displays a window. If the window is minimized or maximized, Windows restores it to its original size and position. An application should specify this flag when displaying the window for the first time.
If lpFile specifies a document file, nShowCmd should be zero.
Return Values
If the function succeeds, the return value is the instance handle of the application that was run, or the handle of a dynamic data exchange (DDE) server application.
If the function fails, the return value is an error value that is less than or equal to 32. The following table lists these error values:
Value Meaning
0 The operating system is out of memory or resources.
ERROR_FILE_NOT_FOUND The specified file was not found.
ERROR_PATH_NOT_FOUND The specified path was not found.
ERROR_BAD_FORMAT The .EXE file is invalid (non-Win32 .EXE or error in .EXE image).
SE_ERR_ACCESSDENIED The operating system denied access to the specified file.
SE_ERR_ASSOCINCOMPLETE The filename association is incomplete or invalid.
SE_ERR_DDEBUSY The DDE transaction could not be completed because other DDE transactions were being processed.
SE_ERR_DDEFAIL The DDE transaction failed.
SE_ERR_DDETIMEOUT The DDE transaction could not be completed because the request timed out.
SE_ERR_DLLNOTFOUND The specified dynamic-link library was not found.
SE_ERR_FNF The specified file was not found.
SE_ERR_NOASSOC There is no application associated with the given filename extension.
SE_ERR_OOM There was not enough memory to complete the operation.
SE_ERR_PNF The specified path was not found.
SE_ERR_SHARE A sharing violation occurred.
Remarks
The file specified by the lpFile parameter can be a document file or an executable file. If the file is a document file, the ShellExecute function opens or prints it, depending on the value of the lpOperation parameter. If the file is an executable file, the ShellExecute function opens it, even if lpOperation specifies printing.
You can use ShellExecute to open or explore a shell folder. To open a folder, use either of the following calls:
ShellExecute(handle, NULL, path_to_folder, NULL, NULL, SW_SHOWNORMAL);
or
ShellExecute(handle, "open", path_to_folder, NULL, NULL, SW_SHOWNORMAL);
To explore a folder, use the following call:
ShellExecute(handle, "explore", path_to_folder, NULL, NULL, SW_SHOWNORMAL);
If lpOperation is NULL, the function opens the file specified by lpFile. If lpOperation is "open" or "explore", the function will force an open window or explorer.
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