From c324c3a9e7558e87ec628d45d3d0577d614ee350 Mon Sep 17 00:00:00 2001
From: Tavian Barnes <tavianator@tavianator.com>
Date: Fri, 22 Mar 2013 21:41:45 -0400
Subject: Use spinlock for futures when possible.

---
 libdimension/future.c | 89 +++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 69 insertions(+), 20 deletions(-)

(limited to 'libdimension/future.c')

diff --git a/libdimension/future.c b/libdimension/future.c
index 6ea15ae..555330f 100644
--- a/libdimension/future.c
+++ b/libdimension/future.c
@@ -41,6 +41,9 @@ dmnsn_new_future(void)
   future->progress = 0;
   future->total    = 1;
 
+#if DMNSN_SPINLOCK
+  dmnsn_initialize_spinlock(&future->spinlock, PTHREAD_PROCESS_PRIVATE);
+#endif
   dmnsn_initialize_mutex(&future->mutex);
   dmnsn_initialize_cond(&future->cond);
 
@@ -67,6 +70,9 @@ dmnsn_future_join(dmnsn_future *future)
     /* Free the future object */
     dmnsn_destroy_cond(&future->cond);
     dmnsn_destroy_mutex(&future->mutex);
+#if DMNSN_SPINLOCK
+    dmnsn_destroy_spinlock(&future->spinlock);
+#endif
     dmnsn_free(future);
   }
 
@@ -80,11 +86,49 @@ dmnsn_future_cancel(dmnsn_future *future)
   pthread_cancel(future->thread);
 }
 
-/**
- * Get the current progress, without locking anything.
- *
- * future->mutex must be locked for this call to be safe.
- */
+/** Lock the appropriate lock for a future. */
+static inline void
+dmnsn_lock_future(const dmnsn_future *future)
+{
+#if DMNSN_SPINLOCK
+  dmnsn_lock_spinlock(&MUTATE(future)->spinlock);
+#else
+  dmnsn_lock_mutex(&MUTATE(future)->mutex);
+#endif
+}
+
+/** Unlock the appropriate lock for a future. */
+static inline void
+dmnsn_unlock_future(const dmnsn_future *future)
+{
+#if DMNSN_SPINLOCK
+  dmnsn_unlock_spinlock(&MUTATE(future)->spinlock);
+#else
+  dmnsn_unlock_mutex(&MUTATE(future)->mutex);
+#endif
+}
+
+/** Lock the future's mutex specifically, if we have the spinlock already. */
+static inline void
+dmnsn_future_exchange_lock(const dmnsn_future *future)
+{
+#if DMNSN_SPINLOCK
+  dmnsn_unlock_spinlock(&MUTATE(future)->spinlock);
+  dmnsn_lock_mutex(&MUTATE(future)->mutex);
+#endif
+}
+
+/** Unlock the future's mutex specifically, if we have the spinlock already. */
+static inline void
+dmnsn_future_exchange_unlock(const dmnsn_future *future)
+{
+#if DMNSN_SPINLOCK
+  dmnsn_unlock_mutex(&MUTATE(future)->mutex);
+  dmnsn_lock_spinlock(&MUTATE(future)->spinlock);
+#endif
+}
+
+/** Get the current progress, without locking anything. */
 static inline double
 dmnsn_future_progress_unlocked(const dmnsn_future *future)
 {
@@ -95,12 +139,11 @@ dmnsn_future_progress_unlocked(const dmnsn_future *future)
 double
 dmnsn_future_progress(const dmnsn_future *future)
 {
-  dmnsn_future *mfuture = MUTATE(future);
   double progress;
 
-  dmnsn_lock_mutex(&mfuture->mutex);
-    progress = dmnsn_future_progress_unlocked(mfuture);
-  dmnsn_unlock_mutex(&mfuture->mutex);
+  dmnsn_lock_future(future);
+    progress = dmnsn_future_progress_unlocked(future);
+  dmnsn_unlock_future(future);
 
   return progress;
 }
@@ -111,24 +154,26 @@ dmnsn_future_wait(const dmnsn_future *future, double progress)
 {
   dmnsn_future *mfuture = MUTATE(future);
 
-  dmnsn_lock_mutex(&mfuture->mutex);
+  dmnsn_lock_future(mfuture);
     while (dmnsn_future_progress_unlocked(mfuture) < progress) {
       /* Set the minimum waited-on value */
       if (progress < mfuture->min_wait)
         mfuture->min_wait = progress;
 
-      dmnsn_cond_wait(&mfuture->cond, &mfuture->mutex);
+      dmnsn_future_exchange_lock(mfuture);
+        dmnsn_cond_wait(&mfuture->cond, &mfuture->mutex);
+      dmnsn_future_exchange_unlock(mfuture);
     }
-  dmnsn_unlock_mutex(&mfuture->mutex);
+  dmnsn_unlock_future(mfuture);
 }
 
 /* Set the total number of loop iterations */
 void
 dmnsn_future_set_total(dmnsn_future *future, size_t total)
 {
-  dmnsn_lock_mutex(&future->mutex);
+  dmnsn_lock_future(future);
     future->total = total;
-  dmnsn_unlock_mutex(&future->mutex);
+  dmnsn_unlock_future(future);
 }
 
 /* Increment the number of completed loop iterations */
@@ -140,22 +185,26 @@ dmnsn_future_increment(dmnsn_future *future)
      on cancellation */
   pthread_testcancel();
 
-  dmnsn_lock_mutex(&future->mutex);
+  dmnsn_lock_future(future);
     ++future->progress;
 
     if (dmnsn_future_progress_unlocked(future) >= future->min_wait) {
       future->min_wait = 1.0;
-      dmnsn_cond_broadcast(&future->cond);
+      dmnsn_future_exchange_lock(future);
+        dmnsn_cond_broadcast(&future->cond);
+      dmnsn_future_exchange_unlock(future);
     }
-  dmnsn_unlock_mutex(&future->mutex);
+  dmnsn_unlock_future(future);
 }
 
 /* Immediately set to 100% completion */
 void
 dmnsn_future_done(dmnsn_future *future)
 {
-  dmnsn_lock_mutex(&future->mutex);
+  dmnsn_lock_future(future);
     future->progress = future->total;
-    dmnsn_cond_broadcast(&future->cond);
-  dmnsn_unlock_mutex(&future->mutex);
+    dmnsn_future_exchange_lock(future);
+      dmnsn_cond_broadcast(&future->cond);
+    dmnsn_future_exchange_unlock(future);
+  dmnsn_unlock_future(future);
 }
-- 
cgit v1.2.3