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Boost.ThreadsClass thread |
Introduction
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Synopsis
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Example
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.
#include <boost/thread/thread.hpp>
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
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.
~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()
.
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)
.
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.
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.
#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 01 October, 2001
© Copyright William E. Kempf 2001 all rights reserved.