CancelSynchronousIo function (ioapiset.h)

Marks pending synchronous I/O operations that are issued by the specified thread as canceled.


BOOL CancelSynchronousIo(
  [in] HANDLE hThread


[in] hThread

A handle to the thread.

Return value

If the function succeeds, the return value is nonzero.

If the function fails, the return value is 0 (zero). To get extended error information, call the GetLastError function.

If this function cannot find a request to cancel, the return value is 0 (zero), and GetLastError returns ERROR_NOT_FOUND.


The caller must have the THREAD_TERMINATE access right.

If there are any pending I/O operations in progress for the specified thread, the CancelSynchronousIo function marks them for cancellation. Most types of operations can be canceled immediately; other operations can continue toward completion before they are actually canceled and the caller is notified. The CancelSynchronousIo function does not wait for all canceled operations to complete. For more information, see Canceling Pending I/O Operations.

The operation being canceled is completed with one of three statuses; you must check the completion status to determine the completion state. The three statuses are:

  • The operation completed normally. This can occur even if the operation was canceled, because the cancel request might not have been submitted in time to cancel the operation.
  • The operation was canceled. The GetLastError function returns ERROR_OPERATION_ABORTED.
  • The operation failed with another error. The GetLastError function returns the relevant error code.
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


Requirement Value
Minimum supported client Windows Vista [desktop apps only]
Minimum supported server Windows Server 2008 [desktop apps only]
Target Platform Windows
Header ioapiset.h (include Windows.h)
Library Kernel32.lib
DLL Kernel32.dll

See also



File Management Functions

Synchronous and Asynchronous I/O