Win32 process communication -- the use of mail slot

Keywords: network Windows Unix socket

Post slot

Mail slot is a one-way interprocess communication mechanism provided by Windows operating system, which can be used in single machine or multi machine distributed environment on network. For relatively short low-frequency messages, it is usually easier to use a mail slot than a named pipe or Unix domain socket.

Three simple messages can be read out:

  • The data transmitted in the mail slot is unidirectional (client - > server)
  • It can communicate between processes or between networks
  • Small data per transmission (400B)

Name of mail slot:

  • \\. \ \ mailslot\[path\]name – > native
  • \\DomainName\[path\]name – > network domain name
  • \\ComputerName\[path\]name – > network computer name
  • \\*\mailslot\[path\]name -- > broadcast

In this case, mail slot will be used to realize communication between two processes, and the first name will be selected

Thinking analysis:

  • The server creates a mail slot and waits for the data to arrive and read
  • Client opens mail slot and writes data

The effect of the case is shown in the figure:

Server window and function realization steps:

  1. Window building and user-defined ID Name:

  1. Associate a variable for the button:
  2. Double click the receive button to realize the function of receiving data for the server:

m_b.EnableWindow(0);			// Make the button unselectable
m_b.SetWindowText(_T("Reading..."));	// Set the contents of the button

// Create slot / / = =/
HANDLE hmailslot = CreateMailslot(_T("\\\\.\\mailslot\\MyMailslot"),
    0, MAILSLOT_WAIT_FOREVER, NULL);		// Create a mail slot and wait for the data to arrive

if(hmailslot == INVALID_HANDLE_VALUE)	// Determine whether the mail slot is successfully created
    m_b.EnableWindow(1);		// Change the button back (can be selected)
    m_b.SetWindowText(_T("Receive"));	// The content has changed back
    AfxMessageBox(_T("CreateMailslot error"));

TCHAR buf[400];		// It is used to receive the data obtained from the mail slot. The maximum can only be 400
ZeroMemory(buf, 400);	// Qing 0

DWORD dwRead;	// Number of data actually read
// Read the contents of the mail slot in the same way as the file
if(!ReadFile(hmailslot, buf, 400, &dwRead, NULL))	
    m_b.EnablWindow(1);	// If the reading fails, the button will be restored

    AfxMessageBox(_T("ReadFile error"));
    CloseHandle(hmailslot);	// Failed to read the file, close the handle of the mail slot

SetDlgItemText(IDC_EDIT_DATA, buf); // Put the read into the edit box

m_b.EnableWindow(1);	// Button restore

Client window and function realization steps:

  1. Interface building and custom control ID:

  1. Double click the send button to send data to the client:

// Open the mail slot (the essence of the mail slot is a file) see the code below for the meaning of the parameters
HANDLE hMailslot = CreateFile(_T("\\\\.\\mailslot\\MyMailslot"),

if(hMailslot == INVALID_HANDLE_VALUE)	// Fail to open mail slot
    AfxMessageBox(_T("Open mailslot failed."));
    return 0;

TCHAR buf[400];		// Buffer for storing data, the maximum can only be 400
ZeroMemory(buf, 400);	// Qing 0

GetDlgItemText(IDC_EDIT_DATA, buf, 400); // Get data in control
DWORD dwWrite;	// Number of data actually written

if(!WriteFile(hMailslot, buf, 400, &dwWrite, NULL))
    CloseHandle(hMailslot);	// Failed to write data, closing handle
    AfxMessageBox(_T("Failed to send data!"));

CloseHandle(hMailslot);	 // Closing handle

The meaning of each parameter of CreateFile is shown in (2) Win32 process communication -- memory mapping file Mentioned in

Author: the dream of prodigal son

Time: 2020.02.14

Happy Valentine's day, everyone

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Posted by supergrover1981 on Fri, 14 Feb 2020 05:56:33 -0800