MailSlot

From Wikipedia, the free encyclopedia

A MailSlot is a type of interprocess communication that allows communication between processes both locally and over a network. The use of MailSlots is generally simpler than named pipes or sockets, but they are more limited.

1 Features
2 Implementations
3 Example Code
4 External links

[edit] Features

MailSlots function as a server-client interface. A server can create a MailSlot, and a client can write to it. Only the server can read the mailslot. A server-client interface could consist of two processes communicating locally or across a network. MailSlots do not operate over Wide Area Networks such as the internet, though. Also, MailSlots offer no confirmation that a message has been received unless it is programmed into an application. MailSlots are generally a good choice when one process must broadcast a message to multiple processes, or if a fast and very easy solution is needed.

[edit] Implementations

The most widely known implementation of the MailSlot is the Messenger Service that exists in Windows XP. The Messenger Service is essentially a MailSlot server that waits for a message to arrive. When a message arrives it is displayed in a popup onscreen. The NET SEND command is therefore a type of MailSlot client, because it writes to specified mailslots on a network.

A number of programs also use MailSlots to communicate. Generally these are amateur chat clients and other such programs. Commercial programs usually prefer pipes or sockets.

KNOWN MAILSLOTS

MAILSLOT\Messngr - Microsoft NET SEND Protocol
MAILSLOT\Browse - Microsoft Browser Protocol
MAILSLOT\Alerter
MAILSLOT\53cb31a0\UnimodemNotifyTSP
MAILSLOT\HydraLsServer - Microsoft Terminal Services Licensing
MAILSLOT\CheyenneDS - CA BrightStor Discovery Service

[edit] Example Code

Creating a Mailslot on a server, to be read (only).

/* Create a mail slot named blort, allowing any size records
 * to be received (up to 64K). Specify that we'll wait forever
 * when reading a record.
 */
HANDLE handle;

handle = CreateMailslot("\\\\.\\mailslot\\blort",
         0,
         MAILSLOT_WAIT_FOREVER,
         NULL);
if (handle == INVALID_HANDLE_VALUE) 
{
   printf("CreateMailslot failed: %d\n", GetLastError());
}

Opening a Mailslot on a client, to send data to it.

/* Open the blort mailslot on MyComputer */
HANDLE   handle;

handle = CreateFile("\\\\MyComputer\\mailslot\\blort",
   GENERIC_WRITE, 
   FILE_SHARE_READ,
   0, 
   OPEN_EXISTING, 
   FILE_ATTRIBUTE_NORMAL, 
   0); 
if (handle == INVALID_HANDLE_VALUE) 
{
   printf("CreateFile failed: %d\n", GetLastError());
}