Changeset 1c56bf7 for libcfa/src/concurrency

Timestamp:

Jun 10, 2022, 2:59:21 PM (2 years ago)

Author:

Thierry Delisle <tdelisle@…>

Branches:

ADT, ast-experimental, master, pthread-emulation, qualifiedEnum

Children:

f3da205

Parents:

6d41f66

Message:

Fixed retract to not reset the future when retracting.

File:

• libcfa/src/concurrency/kernel/fwd.hfa (modified) (1 diff)

libcfa/src/concurrency/kernel/fwd.hfa

@@ -274 +274 @@
                         // intented to be use by wait, wait_any, waitfor, etc. rather than used directly
                         bool retract( future_t & this, oneshot & wait_ctx ) {
-                                // Remove the wait context
-                                struct oneshot * got = __atomic_exchange_n( &this.ptr, 0p, __ATOMIC_SEQ_CST);
-
-                                // got == 0p: future was never actually setup, just return
-                                if( got == 0p ) return false;
-
-                                // got == wait_ctx: since fulfil does an atomic_swap,
-                                // if we got back the original then no one else saw context
-                                // It is safe to delete (which could happen after the return)
-                                if( got == &wait_ctx ) return false;
-
-                                // got == 1p: the future is ready and the context was fully consumed
-                                // the server won't use the pointer again
-                                // It is safe to delete (which could happen after the return)
-                                if( got == 1p ) return true;
-
-                                // got == 2p: the future is ready but the context hasn't fully been consumed
-                                // spin until it is safe to move on
-                                if( got == 2p ) {
-                                        while( this.ptr != 1p ) Pause();
-                                        return false;
-                                }
-
-                                // got == any thing else, something wen't wrong here, abort
-                                abort("Future in unexpected state");
+                                for() {
+                                        struct oneshot * expected = this.ptr;
+
+                                        // expected == 0p: future was never actually setup, just return
+                                        if( expected == 0p ) return false;
+
+                                        // expected == 1p: the future is ready and the context was fully consumed
+                                        // the server won't use the pointer again
+                                        // It is safe to delete (which could happen after the return)
+                                        if( expected == 1p ) return true;
+
+                                        // expected == 2p: the future is ready but the context hasn't fully been consumed
+                                        // spin until it is safe to move on
+                                        if( expected == 2p ) {
+                                                while( this.ptr != 1p ) Pause();
+                                                /* paranoid */ verify( this.ptr != 1p );
+                                                return true;
+                                        }
+
+                                        // expected != wait_ctx: the future was setup with a different context ?!?!
+                                        // something went wrong here, abort
+                                        if( expected != &wait_ctx ) abort("Future in unexpected state");
+
+                                        // we still have the original context, then no one else saw it
+                                        // attempt to remove the context so it doesn't get consumed.
+                                        if(__atomic_compare_exchange_n( &this.ptr, &expected, 0p, false, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST)) {
+                                                return false;
+                                        }
+                                }
                         }