add example for filament

example/Jamfile.v2

@@ -110,6 +110,10 @@ exe unwind_default
     : unwind_default.cpp
     ;
 
+exe filament
+    : filament.cpp
+    ;
+
 #exe backtrace
 #    : backtrace.cpp
 #    ;

example/filament.cpp

@@ -0,0 +1,111 @@
+//          Copyright Oliver Kowalke 2019.
+// Distributed under the Boost Software License, Version 1.0.
+//    (See accompanying file LICENSE_1_0.txt or copy at
+//          http://www.boost.org/LICENSE_1_0.txt)
+
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+#include <queue>
+
+#include <unwind.h>
+
+#include <boost/context/fiber_context.hpp>
+
+namespace ctx = boost::context;
+
+class filament {
+private:
+    std::queue< filament >  &   q_;
+    ctx::fiber_context          f_;
+
+public:
+    filament( std::queue< filament > & q) :
+        q_{ q },
+        f_{} {
+    }
+
+    template< typename Fn >
+    filament( std::queue< filament > & q, Fn && fn) :
+        q_{ q },
+        f_{ [this,fn=std::forward<Fn>(fn)](ctx::fiber_context &&)->ctx::fiber_context{
+            fn( [this](){
+                    // deque next filament
+                    filament next = std::move( q_.front() );
+                    q_.pop();
+                    // queue this filament
+                    q_.push( std::move( * this) );
+                    // resume next filament
+                    q_.back().resume_next( next);
+                });
+            return {};
+        }} {
+    }
+
+    ~filament() {
+        if ( f_) {
+            // unwind the filament's stack
+            std::move( f_).resume_with( ctx::unwind_fiber);
+        }
+    }
+
+    filament( filament const&) = delete;
+    filament & operator=( filament const&) = delete;
+
+    filament( filament && other):
+        q_{ other.q_ },
+        f_{} {
+        other.f_.swap( f_);
+    }
+
+    filament & operator=( filament && other) {
+        if ( this != & other) {
+            other.q_.swap( q_);
+            other.f_.swap( f_);
+        }
+        return * this;
+    }
+
+    void resume_next( filament & fila) {
+        std::move( fila.f_).resume_with([this](ctx::fiber_context&& f)->ctx::fiber_context {
+            // store filament's suspended fiber_context
+            f_ = std::move( f);
+            return {};
+        });
+    }
+
+};
+
+int main( int argc, char * argv[]) {
+    std::queue< filament > q;
+    filament main{ q };
+    unsigned int count = 3;
+    filament f1{
+        q,
+        [count,&q,&main](std::function<void()> && next){
+            for ( unsigned int i = 1; i <= count; ++i) {
+                std::printf("ping\n");
+                if ( i == count) {
+                    // queue the filament `main` to 
+                    // resume it at the end of the loop
+                    q.push( std::move( main) );
+                }
+                // resume next filament
+                next();
+            }
+        }};
+    filament f2{
+        q,
+        [count](std::function<void()> && next){
+            for ( unsigned int i = 1; i <= count; ++i) {
+                std::printf("pong\n");
+                // resume next filament
+                next();
+            }
+        }};
+    // queue filament `f2`
+    q.push( std::move( f2) );
+    // resume filament `f1`
+    main.resume_next( f1);
+    return EXIT_SUCCESS;
+}