Allocates a thread local storage (TLS) index. Any thread of the process can subsequently use this index to store and retrieve values that are local to the thread, because each thread receives its own slot for the index.

Syntax

DWORD WINAPI TlsAlloc(void);

Parameters

Return Value

If the function succeeds, the return value is a TLS index. The slots for the index are initialized to zero.

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

Remarks

The threads of the process can use the TLS index in subsequent calls to the TlsFree, TlsSetValue, or TlsGetValue functions. The value of the TLS index should be treated as an opaque value; do not assume that it is an index into a zero-based array.

TLS indexes are typically allocated during process or dynamic-link library (DLL) initialization. After a TLS index has been allocated, each thread of the process can use it to access its own TLS storage slot. To store a value in its TLS slot, a thread specifies the index in a call to TlsSetValue. The thread specifies the same index in a subsequent call to TlsGetValue, to retrieve the stored value.

TLS indexes are not valid across process boundaries. A DLL cannot assume that an index assigned in one process is valid in another process.

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

TlsFree

TlsGetValue

TlsSetValue

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Build date: 10/8/2009