From a344247f075651bdb2093d7c35a9d73dfea0ffa5 Mon Sep 17 00:00:00 2001
From: Oliver Kowalke <oliver.kowalke@gmx.de>
Date: Wed, 25 Nov 2015 19:30:25 +0100
Subject: [PATCH] remove forced_unwind and related functions

- unwinding the stack via exception is not always necessary
- usually a fiber returns from its fiber-fn (stack is already unwound)
- if a fiber has to terminate, interrupt that fiber
---
 include/boost/fiber/context.hpp    | 17 ++---------------
 include/boost/fiber/exceptions.hpp |  2 --
 src/context.cpp                    |  7 -------
 src/scheduler.cpp                  |  7 ++-----
 4 files changed, 4 insertions(+), 29 deletions(-)

diff --git a/include/boost/fiber/context.hpp b/include/boost/fiber/context.hpp
index 4b592a99..b0777c26 100644
--- a/include/boost/fiber/context.hpp
+++ b/include/boost/fiber/context.hpp
@@ -134,8 +134,7 @@ private:
         flag_worker_context         = 1 << 3,
         flag_terminated             = 1 << 4,
         flag_interruption_blocked   = 1 << 5,
-        flag_interruption_requested = 1 << 6,
-        flag_forced_unwind          = 1 << 7
+        flag_interruption_requested = 1 << 6
     };
 
     struct BOOST_FIBERS_DECL fss_data {
@@ -284,14 +283,8 @@ public:
                         std::function< void() > * func( static_cast< std::function< void() > * >( vp) );
                         ( * func)();
                     }
-                    // check for unwinding
-                    if ( ! unwinding_requested() ) {
-                        boost::context::detail::do_invoke( fn, tpl);
-                    }
+                    boost::context::detail::do_invoke( fn, tpl);
                 } catch ( fiber_interrupted const&) {
-                } catch ( forced_unwind const&) {
-                } catch ( ... ) {
-                    std::terminate();
                 }
                 // terminate context
                 terminate();
@@ -361,12 +354,6 @@ public:
 
     void request_interruption( bool req) noexcept;
 
-    bool unwinding_requested() const noexcept {
-        return 0 != ( flags_ & flag_forced_unwind);
-    }
-
-    void request_unwinding() noexcept;
-
     void * get_fss_data( void const * vp) const;
 
     void set_fss_data(
diff --git a/include/boost/fiber/exceptions.hpp b/include/boost/fiber/exceptions.hpp
index 5af77655..b02d68ae 100644
--- a/include/boost/fiber/exceptions.hpp
+++ b/include/boost/fiber/exceptions.hpp
@@ -24,8 +24,6 @@
 namespace boost {
 namespace fibers {
 
-struct forced_unwind {};
-
 class fiber_exception : public std::system_error {
 public:
     fiber_exception() :
diff --git a/src/context.cpp b/src/context.cpp
index 55f74733..b2bfad72 100644
--- a/src/context.cpp
+++ b/src/context.cpp
@@ -334,13 +334,6 @@ context::request_interruption( bool req) noexcept {
     }
 }
 
-void
-context::request_unwinding() noexcept {
-    BOOST_ASSERT( ! is_main_context() );
-    BOOST_ASSERT( ! is_dispatcher_context() );
-    flags_ |= flag_forced_unwind;
-}
-
 void *
 context::get_fss_data( void const * vp) const {
     uintptr_t key( reinterpret_cast< uintptr_t >( vp) );
diff --git a/src/scheduler.cpp b/src/scheduler.cpp
index 84bb1a04..999846b0 100644
--- a/src/scheduler.cpp
+++ b/src/scheduler.cpp
@@ -34,9 +34,6 @@ scheduler::resume_( context * active_ctx, context * ctx, std::function< void() >
     // resume active-fiber == ctx
     ctx->resume( func);
     BOOST_ASSERT( context::active() == active_ctx);
-    if ( active_ctx->unwinding_requested() ) {
-        throw forced_unwind();
-    }
 }
 
 context *
@@ -185,7 +182,7 @@ scheduler::dispatch() {
     // loop till all context' have been terminated
     std::unique_lock< detail::spinlock > lk( worker_splk_);
     while ( ! worker_queue_.empty() ) {
-        // force unwinding of all context' in worker-queue
+        // interrupt all context' in worker-queue
         worker_queue_t::iterator e = worker_queue_.end();
         for ( worker_queue_t::iterator i = worker_queue_.begin(); i != e;) {
             context * ctx = & ( worker_queue_.front() );
@@ -194,7 +191,7 @@ scheduler::dispatch() {
             if ( ctx->is_terminated() ) {
                 i = worker_queue_.erase( i);
             } else {
-                ctx->request_unwinding();
+                ctx->request_interruption( true);
                 set_ready( ctx);
                 ++i;
             }