# Boost.Threads, thread
Keywords: threads, Boost.Threads, thread library, C++

###

# Boost.Threads

## Class thread

Introduction
Header
Synopsis
Members
Example

## Introduction

The `thread` class represents threads of execution, and provides the functionality to create and manage threads within the Boost.Threads library. See Definitions for a precise description of "thread of execution", and for definitions of threading related terms and of thread states such as "blocked".

A thread of execution has an initial function. For the program's initial thread, the initial function is `main()`. For other threads, the initial function is `operator()` of the function object passed to the class `thread` constructor.

A thread of execution is said to be "finished" or "finished execution" when its initial function returns or is terminated. This includes completion of all thread cleanup handlers, and completion of the normal C++ function return behaviors, such as destruction of automatic storage (stack) objects and releasing any associated implementation resources.

A thread object has an associated state which is either "joinable" or "non-joinable".

Except as described below, the policy used by an implementation of Boost.Threads to schedule transitions between thread states is unspecified.

Note: Just as the lifetime of a file may be different from the lifetime of an iostream object which represents the file, the lifetime of a thread of execution may be different from the `thread` object which represents the thread of execution. In particular, after a call to `join()`, the thread of execution will no longer exist even though the `thread` object continues to exist until the end of its normal lifetime. The converse is also possible; if a `thread` object is destroyed without `join()` having first been called, the thread of execution continues until its initial function completes.

## Header

    #include <boost/thread/thread.hpp>

## Synopsis

    namespace boost {

    class thread : boost::noncopyable // Exposition only.
       // Class thread meets the NonCopyable requirement.
    {
    public:
        thread();
        explicit thread(const boost::function0<void>& threadfunc);
        ~thread();

        bool operator==(const thread& rhs) const;
        bool operator!=(const thread& rhs) const;

        void join();

        static void sleep(const xtime& xt);
        static void yield();
    };

    } // namespace boost

## Members

### Constructors

        thread();

Effects: Constructs a `thread` object representing the current thread of execution.

Postcondition: `*this` is non-joinable.

Danger: `*this` is valid only within the current thread.

        thread(const boost::function0<void>& threadfunc);

Effects: Starts a new thread of execution and constructs a `thread` object representing it. Copies `threadfunc` (which in turn copies the function object wrapped by `threadfunc`) to an internal location which persists for the lifetime of the new thread of execution. Calls `operator()` on the copy of the `threadfunc` function object in the new thread of execution.

Postcondition: `*this` is joinable.

Throws: `boost::thread_resource_error` if a new thread of execution cannot be started.

### Destructor

        ~thread();

Effects: Destroys `*this`. The actual thread of execution may continue to execute after the `thread` object has been destroyed.

Notes: If `*this` is joinable the actual thread of execution becomes "detached". Any resources used by the thread will be reclaimed when the thread of execution completes. To ensure such a thread of execution runs to completion before the `thread` object is destroyed, call `join()`.

### Comparison Operators

        bool operator==(const thread& rhs);

Requires: The thread is non-terminated or `*this` is joinable.

Returns: `true` if `*this` and `rhs` represent the same thread of execution.

        bool operator!=(const thread& rhs);

Returns: `!(*this==rhs)`.

### join

        void join();

Requires: `*this` is joinable.

Effects: The current thread of execution blocks until the initial function of the thread of execution represented by `*this` finishes and all resources are reclaimed.

Postcondition: `*this` is non-joinable.

Note: If `*this == thread()` the result is implementation defined. If the implementation doesn't detect this the result will be deadlock.

### sleep

        static void sleep(const xtime& xt);

Effects: The current thread of execution blocks until `xt` is reached.

### yield

        static void yield();

Effects: The current thread of execution is placed in the "ready" state.

Notes: Allow the current thread to give up the rest of its time slice (or other scheduling quota) to another thread. Particularly useful in non-preemptive implementations.

## Example Usage

    #include <boost/thread/thread.hpp>
    #include <iostream>

    struct thread_alarm
    {
       thread_alarm(int secs) : m_secs(secs) { }
       void operator()()
       {
           boost::xtime xt;
           boost::xtime_get(&xt, boost::TIME_UTC);
           xt.sec += m_secs;

           boost::thread::sleep(xt);

           std::cout << "alarm sounded..." << std::endl;
       }

       int m_secs;
    };

    int main(int argc, char* argv[])
    {
       int secs = 5;
       std::cout << "setting alarm for 5 seconds..." << std::endl;
       boost::thread thrd(thread_alarm(secs));
       thrd.join();
    }

The output is:

    setting alarm for 5 seconds...
    alarm sounded...

Revised 05 November, 2001

© Copyright William E. Kempf 2001 all rights reserved.