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Cancels all pending input and output (I/O) operations that are issued by the calling thread for the specified file. The function does not cancel I/O operations that other threads issue for a file handle.
To cancel I/O operations from another thread, use the CancelIoEx function.
Syntax
BOOL CancelIo(
[in] HANDLE hFile
);
Parameters
[in] hFile
A handle to the file.
The function cancels all pending I/O operations for this file handle.
Return value
If the function succeeds, the return value is nonzero. The cancel operation for all pending I/O operations issued by the calling thread for the specified file handle was successfully requested. The thread can use the GetOverlappedResult function to determine when the I/O operations themselves have been completed.
If the function fails, the return value is zero (0). To get extended error information, call the GetLastError function.
Remarks
If there are any pending I/O operations in progress for the specified file handle, and they are issued by the calling thread, the CancelIo function cancels them. CancelIo cancels only outstanding I/O on the handle, it does not change the state of the handle; this means that you cannot rely on the state of the handle because you cannot know whether the operation was completed successfully or canceled.
The I/O operations must be issued as overlapped I/O. If they are not, the I/O operations do not return to allow the thread to call the CancelIo function. Calling the CancelIo function with a file handle that is not opened with FILE_FLAG_OVERLAPPED does nothing.
All I/O operations that are canceled complete with the error ERROR_OPERATION_ABORTED, and all completion notifications for the I/O operations occur normally.
In Windows 8 and Windows Server 2012, this function is supported by the following technologies.
| Technology | Supported |
|---|---|
| Server Message Block (SMB) 3.0 protocol | Yes |
| SMB 3.0 Transparent Failover (TFO) | Yes |
| SMB 3.0 with Scale-out File Shares (SO) | Yes |
| Cluster Shared Volume File System (CsvFS) | Yes |
| Resilient File System (ReFS) | Yes |
Requirements
| Requirement | Value |
|---|---|
| Minimum supported client | Windows XP [desktop apps | UWP apps] |
| Minimum supported server | Windows Server 2003 [desktop apps | UWP apps] |
| Target Platform | Windows |
| Header | ioapiset.h (include Windows.h) |
| Library | Kernel32.lib |
| DLL | Kernel32.dll |