###  | # Boost.Threads ## Header <boost/thread/tss.hpp>

## Contents

Introduction
Classes

Class `thread_specific_ptr`

Class `thread_specific_ptr` synopsis
Class `thread_specific_ptr` constructors and destructor
Class `thread_specific_ptr` modifier functions
Class `thread_specific_ptr` observer functions

Example(s)

## Introduction

The header <boost/thread/tss.hpp> defines the class thread_specific_ptr which is used to manage data associated with specific thread instances.

## Classes

### Class `thread_specific_ptr`

The `thread_specific_ptr` class defines an interface for using thread specific storage. Thread specific storage is data associated with individual threads and is often used to make operations thread-safe that rely on global data.

Template `thread_specific_ptr` stores a pointer to an object obtained via `new` on a thread-by-thread basis and calls delete on the contained pointer when the thread terminates. Each thread initially stores the null pointer in each `thread_specific_ptr` instance.

The template `thread_specific_ptr` is useful in the following cases:

- An interface was originally written assuming a single thread of control and is being ported to a multithreaded environment.
- Each thread of control invokes sequences of methods that share data that must be logically accessed through a globally visible access point, but are physically unique for each thread, instead of being explicitly passed.

#### Class `thread_specific_ptr` synopsis

    namespace boost
    {
        template <typename T>
        class thread_specific_ptr : private boost::noncopyable // Exposition only.
            // Class thread_specific_ptr meets the NonCopyable requirement.
        {
        public:
            thread_specific_ptr();
            ~thread_specific_ptr();

            T* get() const;
            T* operator->() const;
            T& operator*() const;
            T* release();
            void reset(T* p=0);
        };
    };

#### Class `thread_specific_ptr` constructors and destructor

    thread_specific_ptr();

Requires: The expression `delete get()` is well formed.
Postconditions: A thread specific storage has been reserved for use by `*this` in all threads, with each thread initially storing a null pointer.
Throws: `boost::thread_resource_error` if the necessary resources can not be obtained.
Note: There is an implementation specific limit to the number of thread specific storage objects that can be created, and this limit may be small.

    ~thread_specific_ptr();

Note: Does not destroy any data that may be stored in any thread's thread specific storage. For this reason you should not destroy a `thread_specific_ptr` object until you are certain there are no threads running that have made use of its thread specific storage.

#### Class `thread_specific_ptr` modifier functions

    T* release();

Postconditions: `*this` holds the null pointer for the current thread.
Returns: `this->get()` prior to the call.

    void reset(T* p=0);

Effects: If `this->get()!= p` then `delete this->get()`.
Postconditions: `*this` holds the pointer `p` for the current thread.
Note: The pointer will be deleted when the thread terminates.

#### Class `thread_specific_ptr` observer functions

    T* get() const;

Returns: The object stored in thread specific storage for the current thread for `*this`.
Note: Each thread initially returns 0.

    T* operator->() const;

Returns: `this-<get()`.

    T& operator*() const;

Requires: `this-<get() != 0`
Returns: `this-<get()`.

## Example(s)

libs/thread/example/tss.cpp

Revised 05 November, 2001

© Copyright William E. Kempf 2001-2002. All Rights Reserved.

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