Changeset 5f5a729

Timestamp:

Nov 17, 2021, 11:17:59 AM (2 years ago)

Author:

Thierry Delisle <tdelisle@…>

Branches:

ADT, ast-experimental, enum, forall-pointer-decay, master, pthread-emulation, qualifiedEnum

Children:

84a6e70

Parents:

1387ea0

Message:

Mark idle now uses try_lock semantics

Location:

libcfa/src/concurrency

Files:

• kernel.cfa (modified) (5 diffs)
• kernel_private.hfa (modified) (1 diff)

libcfa/src/concurrency/kernel.cfa

@@ -124 +124 @@
 static void __wake_one(cluster * cltr);
 
-static void mark_idle (__cluster_proc_list & idles, processor & proc);
+static bool mark_idle (__cluster_proc_list & idles, processor & proc);
 static void mark_awake(__cluster_proc_list & idles, processor & proc);
 static [unsigned idle, unsigned total, * processor] query_idles( & __cluster_proc_list idles );
@@ -213 +213 @@
 
                                 // Push self to idle stack
-                                mark_idle(this->cltr->procs, * this);
+                                if(!mark_idle(this->cltr->procs, * this)) continue MAIN_LOOP;
 
                                 // Confirm the ready-queue is empty
@@ -331 +331 @@
                                 // Push self to idle stack
                                 ready_schedule_unlock();
-                                mark_idle(this->cltr->procs, * this);
+                                if(!mark_idle(this->cltr->procs, * this)) goto SEARCH;
                                 ready_schedule_lock();
 
@@ -806 +806 @@
 }
 
-static void mark_idle(__cluster_proc_list & this, processor & proc) {
-        /* paranoid */ verify( ! __preemption_enabled() );
-        lock( this );
+static bool mark_idle(__cluster_proc_list & this, processor & proc) {
+        /* paranoid */ verify( ! __preemption_enabled() );
+        if(!try_lock( this )) return false;
                 this.idle++;
                 /* paranoid */ verify( this.idle <= this.total );
@@ -815 +815 @@
         unlock( this );
         /* paranoid */ verify( ! __preemption_enabled() );
+
+        return true;
 }
 

libcfa/src/concurrency/kernel_private.hfa

@@ -282 +282 @@
 }
 
+static inline bool try_lock(__cluster_proc_list & this) {
+        /* paranoid */ verify( ! __preemption_enabled() );
+
+        // Start by locking the global RWlock so that we know no-one is
+        // adding/removing processors while we mess with the idle lock
+        ready_schedule_lock();
+
+        // Simple counting lock, acquired, acquired by incrementing the counter
+        // to an odd number
+        uint64_t l = this.lock;
+        if(
+                (0 == (l % 2))
+                && __atomic_compare_exchange_n(&this.lock, &l, l + 1, false, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST)
+        ) {
+                // success
+                /* paranoid */ verify( ! __preemption_enabled() );
+                return true;
+        }
+
+        // failed to lock
+        ready_schedule_unlock();
+
+        /* paranoid */ verify( ! __preemption_enabled() );
+        return false;
+}
+
 static inline void unlock(__cluster_proc_list & this) {
         /* paranoid */ verify( ! __preemption_enabled() );