From: Dale Martenson <dmartenson@...>
Date: 2002-03-27T03:44:36+09:00
Subject: RE: File change notification?

>> Is there a straightforward way of getting notified when a file
>> changes? In NT I can block a thread on the handle returned by
>> FindFirstChangeNotification. Does something like this exist in Ruby?
>> I'm currently using the Cygwin version but could be convinced to
>> switch.

My first example was a Ruby-way of monitoring a specific file based on it
modification date. Here is a way of call the Win32 API directly from Ruby to
accomplish the task. Is this what you were looking for?


# -----------------------------------------------------------------------
# WARNING: Win32 Specific code to follow -- You have been warned!!
# -----------------------------------------------------------------------

require 'Win32API'

# -----------------------------------------------------------------------
# definitions for Windows constants
# -----------------------------------------------------------------------

INVALID_HANDLE_VALUE = -1

INFINITE = 0xFFFFFFFF

WAIT_OBJECT_0 = 0x00000000

FILE_NOTIFY_CHANGE_FILE_NAME   = 0x00000001   
FILE_NOTIFY_CHANGE_DIR_NAME    = 0x00000002   
FILE_NOTIFY_CHANGE_ATTRIBUTES  = 0x00000004   
FILE_NOTIFY_CHANGE_SIZE        = 0x00000008   
FILE_NOTIFY_CHANGE_LAST_WRITE  = 0x00000010   
FILE_NOTIFY_CHANGE_LAST_ACCESS = 0x00000020   
FILE_NOTIFY_CHANGE_CREATION    = 0x00000040   
FILE_NOTIFY_CHANGE_SECURITY    = 0x00000100   

# -----------------------------------------------------------------------
# Definitions for Windows function calls
# -----------------------------------------------------------------------

# HANDLE FindFirstChangeNotification(
#  LPCTSTR lpPathName,    // directory name
#  BOOL bWatchSubtree,    // monitoring option
#  DWORD dwNotifyFilter   // filter conditions
#);

k32FindFirstChangeNotification = Win32API.new("kernel32",
"FindFirstChangeNotification", ['P', 'I', 'L'], 'L')

# BOOL FindNextChangeNotification(
#  HANDLE hChangeHandle   // handle to change notification
# );

k32FindNextChangeNotification = Win32API.new("kernel32",
"FindNextChangeNotification", ['L'], 'I')

# DWORD WaitForMultipleObjects(
#   DWORD nCount,             // number of handles in array
#   CONST HANDLE *lpHandles,  // object-handle array
#   BOOL bWaitAll,            // wait option
#   DWORD dwMilliseconds      // time-out interval
# );

k32WaitForMultipleObjects = Win32API.new("kernel32",
"WaitForMultipleObjects", ['L', 'P', 'I', 'L'], 'L')

# -----------------------------------------------------------------------
# Create notification events
# -----------------------------------------------------------------------
dwChangeHandles = []

# Watch the C:\WINDOWS directory for file creation and 
# deletion.

dwChangeHandles[0] = k32FindFirstChangeNotification.Call( 
    "C:\\WINDOWS",                 # directory to watch 
    0,                             # do not watch the subtree 
    FILE_NOTIFY_CHANGE_FILE_NAME)  # watch file name changes 
 
if dwChangeHandles[0] == INVALID_HANDLE_VALUE then 
    exit
end    
 
# Watch the C:\ subtree for directory creation and 
# deletion. 
 
dwChangeHandles[1] = k32FindFirstChangeNotification.Call( 
    "C:\\",                        # directory to watch 
    1,                             # watch the subtree 
    FILE_NOTIFY_CHANGE_DIR_NAME);  # watch dir. name changes 
 
if dwChangeHandles[1] == INVALID_HANDLE_VALUE then 
    exit
end    
 
# Create storage for two event handles (LONG)
lp_dwChangeHandles = " " * 8

# Pack event handles into newly created storage area to be used for Win32
call
lp_dwChangeHandles = dwChangeHandles.pack("LL")
 
# Change notification is set. Now wait on both notification 
# handles and refresh accordingly. 

while true 
    # Wait for notification.
 
    dwWaitStatus = k32WaitForMultipleObjects.Call(2, lp_dwChangeHandles, 
        0, INFINITE) 

    case dwWaitStatus
        when WAIT_OBJECT_0 
 
        # A file was created or deleted in C:\WINDOWS. 
        # Do what you need to do and restart the 
        # change notification.

            print "#{Time.now}: A file in C:\\WINDOWS was messed with!\n"
	   
            if k32FindNextChangeNotification.Call( 
                    dwChangeHandles[0] ) == 0 then 
                exit 
	    end
 
        when WAIT_OBJECT_0+1 
 
        # A directory was created or deleted in C:\. 
        # Do what you need to do and restart the 
        # change notification.
 
            print "#{Time.now}: The C:\\ directory was messed with!\n"
	    
            if k32FindNextChangeNotification.Call( 
                    dwChangeHandles[1] ) == 0 then 
                exit
            end   		
 
        else 
            exit
    end 
end