gt-support-fiber-safe-thread-local-storage.md

title	description	ms.date	f1_keywords	helpviewer_keywords	ms.assetid
/GT (Support fiber-safe thread-local storage)	The MSVC compiler option /GT enables safe optimizations for thread-local storage data.	07/08/2020	VC.Project.VCCLCompilerTool.EnableFiberSafeOptimizations /gt	/GT compiler option [C++] GT compiler option [C++] thread-local storage static thread-local storage and fiber safety -GT compiler option [C++] fiber-safe static thread-local storage compiler option [C++]	071fec79-c701-432b-9970-457344133159

/GT (Support fiber-safe thread-local storage)

Supports fiber safety for data allocated using static thread-local storage, that is, data allocated with __declspec(thread).

Syntax

/GT

Remarks

Data declared with __declspec(thread) is referenced through a thread-local storage (TLS) array. The TLS array is an array of addresses that the system maintains for each thread. Each address in this array gives the location of thread-local storage data.

A fiber is a lightweight object that consists of a stack and a register context and can be scheduled on various threads. A fiber can run on any thread. Because a fiber may get swapped out and restarted later on a different thread, the compiler mustn't cache the address of the TLS array, or optimize it as a common subexpression across a function call. /GT prevents such optimizations.

To set this compiler option in the Visual Studio development environment

1. Open the project's Property Pages dialog box. For details, see Set C++ compiler and build properties in Visual Studio.

2. Select the Configuration Properties > C/C++ > Optimization property page.

3. Modify the Enable Fiber-safe Optimizations property.

To set this compiler option programmatically

• See xref:Microsoft.VisualStudio.VCProjectEngine.VCCLCompilerTool.EnableFiberSafeOptimizations%2A.

See also

MSVC compiler options
MSVC compiler command-line syntax