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d653cbdcc6
Add a note to the condition_variable::wait_for(..., pred) overload. fiber_specific_ptr::reset() has no default argument. Remove mention of launch policy deferred, since no API accepts a launch policy argument. Copy construction or copy assignment of a shared_future leaves other.valid() unchanged. It won't be 'true' unless it was 'true' before. Mention that [shared_]future::get_exception_ptr() does not invalidate. Note that 'blocks' and 'suspends' are used interchangeably. Add some cross-references; add link to std::allocator_arg_t. Clarify the cross-reference to the paragraph describing BOOST_FIBERS_NO_ATOMICS. Reformat some overly-long source lines.
348 lines
13 KiB
C++
348 lines
13 KiB
C++
// Copyright Nat Goodspeed 2014.
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// Distributed under the Boost Software License, Version 1.0.
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// (See accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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//
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#include <iostream>
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#include <boost/fiber/all.hpp>
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#include <boost/noncopyable.hpp>
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class Verbose: public boost::noncopyable {
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public:
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Verbose( std::string const& d, std::string const& s="stop") :
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desc( d),
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stop( s) {
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std::cout << desc << " start" << std::endl;
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}
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~Verbose() {
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}
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private:
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std::string desc;
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std::string stop;
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};
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//[priority_props
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class priority_props : public boost::fibers::fiber_properties {
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public:
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priority_props( boost::fibers::fiber_context * p):
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fiber_properties( p), /*< Your subclass constructor must accept a
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[^[class_link fiber_context]*] and pass it to
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the `fiber_properties` constructor. >*/
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priority_( 0) {
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}
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int get_priority() const {
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return priority_; /*< Provide read access methods at your own discretion. >*/
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}
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// Call this method to alter priority, because we must notify
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// priority_scheduler of any change.
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void set_priority( int p) {
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/*< It's important to call notify() on any
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change in a property that can affect the
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scheduler's behavior. Therefore, such
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modifications should only be performed
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through an access method. >*/
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// Of course, it's only worth reshuffling the queue and all if we're
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// actually changing the priority.
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if ( p != priority_) {
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priority_ = p;
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notify();
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}
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}
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// The fiber name of course is solely for purposes of this example
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// program; it has nothing to do with implementing scheduler priority.
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// This is a public data member -- not requiring set/get access methods --
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// because we need not inform the scheduler of any change.
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std::string name; /*< A property that does not affect the scheduler does
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not need access methods. >*/
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private:
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int priority_;
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};
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//]
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//[priority_scheduler
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class priority_scheduler : public boost::fibers::sched_algorithm_with_properties< priority_props > {
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private:
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// Much as we would like, we don't use std::priority_queue because it
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// doesn't appear to provide any way to alter the priority (and hence
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// queue position) of a particular item.
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boost::fibers::fiber_context * head_;
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public:
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priority_scheduler() :
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head_( nullptr) {
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}
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// For a subclass of sched_algorithm_with_properties<>, it's important to
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// override the correct awakened() overload.
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/*<< You must override the [member_link sched_algorithm_with_properties..awakened]
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method. This is how your scheduler receives notification of a
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fiber that has become ready to run. >>*/
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virtual void awakened( boost::fibers::fiber_context * f, priority_props & props) {
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int f_priority = props.get_priority(); /*< `props` is the instance of
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priority_props associated
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with the passed fiber `f`. >*/
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// With this scheduler, fibers with higher priority values are
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// preferred over fibers with lower priority values. But fibers with
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// equal priority values are processed in round-robin fashion. So when
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// we're handed a new fiber_context*, put it at the end of the fibers
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// with that same priority. In other words: search for the first fiber
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// in the queue with LOWER priority, and insert before that one.
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boost::fibers::fiber_context ** fp = & head_;
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for ( ; * fp; fp = & ( * fp)->nxt) {
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if ( properties( * fp).get_priority() < f_priority) {
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/*< Use the
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[member_link sched_algorithm_with_properties..properties]
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method to access properties for any ['other] fiber. >*/
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break;
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}
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}
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// It doesn't matter whether we hit the end of the list or found
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// another fiber with lower priority. Either way, insert f here.
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f->nxt = * fp; /*< Note use of the [data_member_link fiber_context..nxt] member. >*/
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* fp = f;
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//<-
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std::cout << "awakened(" << props.name << "): ";
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describe_ready_queue();
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//->
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}
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/*<< You must override the [member_link sched_algorithm_with_properties..pick_next]
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method. This is how your scheduler actually advises the fiber manager
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of the next fiber to run. >>*/
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virtual boost::fibers::fiber_context * pick_next() {
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// if ready queue is empty, just tell caller
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if ( ! head_) {
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return nullptr;
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}
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// Here we have at least one ready fiber. Unlink and return that.
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boost::fibers::fiber_context * f = head_;
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head_ = f->nxt;
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f->nxt = nullptr;
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//<-
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std::cout << "pick_next() resuming " << properties( f).name << ": ";
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describe_ready_queue();
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//->
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return f;
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}
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/*<< You must override [member_link sched_algorithm_with_properties..ready_fibers]
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to inform the fiber manager of the size of your ready queue. >>*/
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virtual std::size_t ready_fibers() const noexcept {
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std::size_t count = 0;
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for ( boost::fibers::fiber_context * f = head_; f; f = f->nxt) {
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++count;
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}
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return count;
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}
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/*<< Overriding [member_link sched_algorithm_with_properties..property_change]
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is optional. This override handles the case in which the running
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fiber changes the priority of another ready fiber: a fiber already in
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our queue. In that case, move the updated fiber within the queue. >>*/
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virtual void property_change( boost::fibers::fiber_context * f, priority_props & props) {
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// Although our priority_props class defines multiple properties, only
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// one of them (priority) actually calls notify() when changed. The
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// point of a property_change() override is to reshuffle the ready
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// queue according to the updated priority value.
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//<-
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std::cout << "property_change(" << props.name << '(' << props.get_priority()
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<< ")): ";
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//->
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// Find 'f' in the queue. Note that it might not be in our queue at
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// all, if caller is changing the priority of (say) the running fiber.
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bool found = false;
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for ( boost::fibers::fiber_context ** fp = & head_; * fp; fp = & ( * fp)->nxt) {
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if ( * fp == f) {
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// found the passed fiber in our list -- unlink it
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found = true;
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* fp = ( * fp)->nxt;
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f->nxt = nullptr;
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break;
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}
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}
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// It's possible to get a property_change() call for a fiber that is
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// not on our ready queue. If it's not there, no need to move it:
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// we'll handle it next time it hits awakened().
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if ( ! found) {
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/*< Your `property_change()` override must be able to
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handle the case in which the passed `f` is not in
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your ready queue. It might be running, or it might be
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blocked. >*/
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//<-
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// hopefully user will distinguish this case by noticing that
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// the fiber with which we were called does not appear in the
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// ready queue at all
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describe_ready_queue();
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//->
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return;
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}
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// Here we know that f was in our ready queue, but we've unlinked it.
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// We happen to have a method that will (re-)add a fiber_context* to
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// the ready queue.
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awakened(f, props);
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}
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//<-
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void describe_ready_queue() {
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if ( ! head_) {
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std::cout << "[empty]";
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} else {
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const char * delim = "";
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for ( boost::fibers::fiber_context * f = head_; f; f = f->nxt) {
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priority_props & props( properties( f) );
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std::cout << delim << props.name << '(' << props.get_priority() << ')';
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delim = ", ";
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}
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}
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std::cout << std::endl;
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}
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//->
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};
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//]
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//[launch
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template< typename Fn >
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boost::fibers::fiber launch( Fn && func, std::string const& name, int priority) {
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boost::fibers::fiber fiber( func);
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priority_props & props( fiber.properties< priority_props >() );
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props.name = name;
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props.set_priority( priority);
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return fiber;
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}
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//]
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void yield_fn() {
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std::string name( boost::this_fiber::properties< priority_props >().name);
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Verbose v( std::string("fiber ") + name);
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for ( int i = 0; i < 3; ++i) {
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std::cout << "fiber " << name << " yielding" << std::endl;
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boost::this_fiber::yield();
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}
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}
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void barrier_fn( boost::fibers::barrier & barrier) {
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std::string name( boost::this_fiber::properties< priority_props >().name);
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Verbose v( std::string("fiber ") + name);
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std::cout << "fiber " << name << " waiting on barrier" << std::endl;
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barrier.wait();
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std::cout << "fiber " << name << " yielding" << std::endl;
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boost::this_fiber::yield();
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}
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//[change_fn
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void change_fn( boost::fibers::fiber & other,
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int other_priority,
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boost::fibers::barrier& barrier) {
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std::string name( boost::this_fiber::properties< priority_props >().name);
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Verbose v( std::string("fiber ") + name);
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//<-
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std::cout << "fiber " << name << " waiting on barrier" << std::endl;
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//->
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barrier.wait();
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// We assume a couple things about 'other':
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// - that it was also waiting on the same barrier
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// - that it has lower priority than this fiber.
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// If both are true, 'other' is now ready to run but is sitting in
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// priority_scheduler's ready queue. Change its priority.
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priority_props & other_props(
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other.properties< priority_props >() );
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//<-
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std::cout << "fiber " << name << " changing priority of " << other_props.name
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<< " to " << other_priority << std::endl;
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//->
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other_props.set_priority( other_priority);
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}
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//]
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//[main
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int main( int argc, char *argv[]) {
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// make sure we use our priority_scheduler rather than default round_robin
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boost::fibers::use_scheduling_algorithm< priority_scheduler >();
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/*= ...*/
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/*=}*/
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//]
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Verbose v("main()");
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// for clarity
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std::cout << "main() setting name" << std::endl;
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//[main_name
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boost::this_fiber::properties< priority_props >().name = "main";
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//]
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std::cout << "main() running tests" << std::endl;
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{
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Verbose v("high-priority first", "stop\n");
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// verify that high-priority fiber always gets scheduled first
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boost::fibers::fiber low( launch( yield_fn, "low", 1) );
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boost::fibers::fiber med( launch( yield_fn, "medium", 2) );
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boost::fibers::fiber hi( launch( yield_fn, "high", 3) );
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std::cout << "main: high.join()" << std::endl;
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hi.join();
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std::cout << "main: medium.join()" << std::endl;
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med.join();
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std::cout << "main: low.join()" << std::endl;
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low.join();
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}
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{
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Verbose v("same priority round-robin", "stop\n");
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// fibers of same priority are scheduled in round-robin order
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boost::fibers::fiber a( launch( yield_fn, "a", 0) );
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boost::fibers::fiber b( launch( yield_fn, "b", 0) );
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boost::fibers::fiber c( launch( yield_fn, "c", 0) );
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std::cout << "main: a.join()" << std::endl;
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a.join();
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std::cout << "main: b.join()" << std::endl;
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b.join();
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std::cout << "main: c.join()" << std::endl;
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c.join();
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}
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{
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Verbose v("barrier wakes up all", "stop\n");
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// using a barrier wakes up all waiting fibers at the same time
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boost::fibers::barrier barrier( 3);
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boost::fibers::fiber low( launch( [&barrier](){ barrier_fn( barrier); }, "low", 1) );
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boost::fibers::fiber med( launch( [&barrier](){ barrier_fn( barrier); }, "medium", 2) );
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boost::fibers::fiber hi( launch( [&barrier](){ barrier_fn( barrier); }, "high", 3) );
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std::cout << "main: low.join()" << std::endl;
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low.join();
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std::cout << "main: medium.join()" << std::endl;
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med.join();
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std::cout << "main: high.join()" << std::endl;
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hi.join();
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}
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{
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Verbose v("change priority", "stop\n");
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// change priority of a fiber in priority_scheduler's ready queue
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boost::fibers::barrier barrier( 3);
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boost::fibers::fiber c( launch( [&barrier](){ barrier_fn( barrier); }, "c", 1) );
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boost::fibers::fiber a( launch( [&c,&barrier]() { change_fn( c, 3, barrier); }, "a", 3) );
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boost::fibers::fiber b( launch( [&barrier](){ barrier_fn( barrier); }, "b", 2) );
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std::cout << "main: a.join()" << std::endl;
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std::cout << "main: a.join()" << std::endl;
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a.join();
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std::cout << "main: b.join()" << std::endl;
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b.join();
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std::cout << "main: c.join()" << std::endl;
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c.join();
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}
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std::cout << "done." << std::endl;
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return EXIT_SUCCESS;
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}
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