Asynchronous file I/O operation demo https://code.msdn.microsoft.com/windowsdesktop/CppAsynchronousIO-a3f7c07d
CONSOLE APPLICATION : CppAsynchronousIO Project Overview
Use:
CppAsynchronousIO demonstrates the asynchronous file I/O operations. A thread performing asynchronous file I/O sends an I/O request to the kernel by calling an appropriate function. If the request is accepted by the kernel, the calling thread continues processing another job until the kernel signals to the thread that the I/O operation is complete. It then interrupts its current job and processes the data from the I/O operation as necessary.
Project Relation:
CppAsynchronousIO - CppSynchronousIO CppAsynchronousIO shows asynchronous I/O operations and CppSynchronousIO demonstrates synchronous I/O.
Code Logic:
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Create/open a file for reading and writing asynchronously by calling CreateFile, specifying the FILE_FLAG_OVERLAPPED flag in the dwFlagsAndAttributes parameter.
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To queue an I/O request for a device driver, call ReadFile and WriteFile with an OVERLAPPED structure.
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To receive completed I/O request notifications, Windows offers four different methods:
a) Signaling a device kernel object: Not useful for performing multiple simultaneous I/O requests against a single device. Allows one thread to issue an I/O request and another thread to process it. (See WaitForDeviceObject)
b) Signaling an event kernel object: Allows multiple simultaneous I/O requests against a single device. Allows one thread to issue an I/O request and another thread to process it. (See: WaitForEventObject and GetOverlappedResult)
c) Using alertable I/O: Allows multiple simultaneous I/O requests against a single device. The thread that issued an I/O request must also process it. (See: AlertableIO)
d) Using I/O completion ports: Allows multiple simultaneous I/O requests against a single device. Allows one thread to issue an I/O request and another thread to process it. This technique is highly scalable and has the most flexibility. (See IoCompletionPort)
References:
MSDN: Synchronous and Asynchronous I/O http://msdn.microsoft.com/en-us/library/aa365683.aspx
Windows via C/C++, Fifth Edition. Basics of Asynchronous Device I/O http://msdn.microsoft.com/en-us/library/cc500408.aspx