TlsSetValue function (processthreadsapi.h)

Stores a value in the calling thread's thread local storage (TLS) slot for the specified TLS index. Each thread of a process has its own slot for each TLS index.

Syntax

BOOL TlsSetValue(
  [in]           DWORD  dwTlsIndex,
  [in, optional] LPVOID lpTlsValue
);

Parameters

[in] dwTlsIndex

The TLS index that was allocated by the TlsAlloc function.

[in, optional] lpTlsValue

The value to be stored in the calling thread's TLS slot for the index.

Return value

If the function succeeds, the return value is nonzero.

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

Remarks

Windows Phone 8.1: This function is supported for Windows Phone Store apps on Windows Phone 8.1 and later. When a Windows Phone Store app calls this function, it is replaced with an inline call to FlsSetValue. Refer to FlsSetValue for function documentation.

Windows 8.1, Windows Server 2012 R2, and Windows 10, version 1507: This function is supported for Windows Store apps on Windows 8.1, Windows Server 2012 R2, and Windows 10, version 1507. When a Windows Store app calls this function, it is replaced with an inline call to FlsSetValue. Refer to FlsSetValue for function documentation.

Windows 10, version 1511 and Windows 10, version 1607: This function is fully supported for Universal Windows Platform (UWP) apps, and is no longer replaced with an inline call to FlsSetValue.

TLS indexes are typically allocated by the TlsAlloc function during process or DLL initialization. When a TLS index is allocated, its storage slots are initialized to NULL. After a TLS index is allocated, each thread of the process can use it to access its own TLS slot for that index. A thread specifies a TLS index in a call to TlsSetValue, to store a value in its slot. The thread specifies the same index in a subsequent call to TlsGetValue, to retrieve the stored value.

TlsSetValue was implemented with speed as the primary goal. The function performs minimal parameter validation and error checking. In particular, it succeeds if dwTlsIndex is in the range 0 through (TLS_MINIMUM_AVAILABLE – 1). It is up to the programmer to ensure that the index is valid before calling TlsGetValue.

Examples

For an example, see Using Thread Local Storage or Using Thread Local Storage in a Dynamic-Link Library.

Requirements

See also

Process and Thread Functions

Thread Local Storage

TlsAlloc

TlsFree

TlsGetValue

Vertdll APIs available in VBS enclaves