Boost.Threads

Header <boost/thread.hpp>

Introduction
Classes
Example(s)

Introduction

The boost/thread.hpp header contains classes used to create and manage threads.

Classes

Class `thread`

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.

Class `thread` 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

Class `thread` constructors and destructor

thread();

Effects: Constructs a thread object representing the current thread of execution.
Postconditions: *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.
Postconditions: *this is joinable.
Throws: boost::thread_resource_error if a new thread of execution cannot be started.

~thread();

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

Class `thread` comparison functions

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

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) const;

Requires: The thread is non-terminated or *this is joinable.
Returns: !(*this==rhs).

Class `thread` modifier functions

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.
Postconditions: *this is non-joinable.
Notes: If *this == thread() the result is implementation defined. If the implementation doesn't detect this the result will be deadlock.

Class `thread` static functions

static void sleep(const xtime& xt);

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

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.

Class `thread_group`

The thread_group class provides a container for easy grouping of threads to simplify several common thread creation and management idioms.

All thread_group member functions are thread-safe, except destruction.

Class `thread_group` synopsis

namespace boost {
    class thread_group : boost::noncopyable
    {
    public:
        thread_group();
        ~thread_group();

        thread* create_thread(const boost::function0<void>& threadfunc);
        void add_thread(thread* thrd);
        void remove_thread(thread* thrd);
        void join_all();
    };
} // namespace boost

Class `thread_group` constructors and destructor

thread_group();

Effects: Constructs an empty thread_group container.

~thread_group();

Effects: Destroys each contained thread object. Destroys *this.
Notes: Behavior is undefined if another thread references *this during the execution of the destructor.

Class `thread_group` modifier functions

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

Effects: Creates a new thread object that executes threadfunc and adds it to the thread_group container object's list of managed thread objects.
Returns: Pointer to the newly created thread.

void add_thread(thread* thrd);

Effects: Adds thrd to the thread_group object's list of managed thread objects. The thrd object must have been allocated via operator new and will be deleted when the group is destroyed.

void remove_thread(thread* thrd);

Effects: Removes *this's list of managed thread objects.
Throws: ? if thrd is not it *this's list of managed thread objects.

void join_all();

Effects: Calls join() on each of the managed thread objects.

Functions

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Effects: {{text}}
Postconditions: {{text}}
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Throws: {{text}}
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Objects

Example(s)

Simple usage of `boost::thread`

#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;
   thread_alarm alarm(secs);
   boost::thread thrd(alarm);
   thrd.join();
}

The output is:

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

Simple usage of `boost::thread_group`

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

int count = 0;
boost::mutex mutex;

void increment_count()
{
   boost::mutex::lock lock(mutex);
   std::cout << "count = " << ++count << std::endl;
}

int main(int argc, char* argv[])
{
   boost::thread_group threads;
   for (int i = 0; i < 10; ++i)
      threads.create_thread(&increment_count);
   threads.join_all();
}

The output is:

count = 1
count = 2
count = 3
count = 4
count = 5
count = 6
count = 7
count = 8
count = 9
count = 10

Revised 05 November, 2001

Boost.Threads

Header <boost/thread.hpp>

Contents

Introduction

Classes

Class thread

Class thread synopsis

Class thread constructors and destructor

Class thread comparison functions

Class thread modifier functions

Class thread static functions

Class thread_group

Class thread_group synopsis

Class thread_group constructors and destructor

Class thread_group modifier functions