1 files changed, 89 insertions, 71 deletions

diff --git a/include/framework/structure/MutableBuffer.h b/include/framework/structure/MutableBuffer.h
index e62a495..7357915 100644
--- a/include/framework/structure/MutableBuffer.h
+++ b/include/framework/structure/MutableBuffer.h
@@ -1,7 +1,7 @@
 /*
  * include/framework/structure/MutableBuffer.h
  *
- * Copyright (C) 2023-2024 Douglas B. Rumbaugh <drumbaugh@psu.edu>
+ * Copyright (C) 2023-2025 Douglas B. Rumbaugh <drumbaugh@psu.edu>
  *                         Dong Xie <dongx@psu.edu>
  *
  * Distributed under the Modified BSD License.
@@ -109,11 +109,11 @@ public:
   size_t get_tombstone_count() const { return m_tscnt.load(); }
 
   bool delete_record(const R &rec) {
-    return get_buffer_view().delete_record(rec);
+    return get_buffer_view(m_head.load().head_idx).delete_record(rec);
   }
 
   bool check_tombstone(const R &rec) {
-    return get_buffer_view().check_tombstone(rec);
+    return get_buffer_view(m_head.load().head_idx).check_tombstone(rec);
   }
 
   size_t get_memory_usage() const { return m_cap * sizeof(Wrapped<R>); }
@@ -122,20 +122,9 @@ public:
     return m_tombstone_filter->get_memory_usage();
   }
 
-  BufferView<R> get_buffer_view(size_t target_head) {
-    size_t head = get_head(target_head);
-    auto f = std::bind(release_head_reference, (void *)this, head);
-
+  BufferView<R> get_buffer_view(size_t head) {
     return BufferView<R>(m_data, m_cap, head, m_tail.load(), m_tscnt.load(),
-                         m_tombstone_filter, f);
-  }
-
-  BufferView<R> get_buffer_view() {
-    size_t head = get_head(m_head.load().head_idx);
-    auto f = std::bind(release_head_reference, (void *)this, head);
-
-    return BufferView<R>(m_data, m_cap, head, m_tail.load(), m_tscnt.load(),
-                         m_tombstone_filter, f);
+                         m_tombstone_filter);
   }
 
   /*
@@ -159,7 +148,7 @@ public:
     // fprintf(stderr, "[I] Refcnts: %ld %ld\n", m_old_head.load().refcnt, m_head.load().refcnt);
     
 
-    buffer_head new_hd = {new_head, 0};
+    buffer_head new_hd = {new_head, 1};
     buffer_head cur_hd;
 
     /* replace current head with new head */
@@ -174,32 +163,6 @@ public:
     return true;
   }
 
-  /*
-   * FIXME: If target_head does not match *either* the old_head or the
-   * current_head, this routine will loop infinitely.
-   */
-  size_t get_head(size_t target_head) {
-    buffer_head cur_hd, new_hd;
-    bool head_acquired = false;
-
-
-    //fprintf(stderr, "[I]: getting head %ld %ld %ld\n", target_head, m_old_head.load().head_idx, m_head.load().head_idx);
-    do {
-      if (m_old_head.load().head_idx == target_head) {
-        cur_hd = m_old_head.load();
-        cur_hd.head_idx = target_head;
-        new_hd = {cur_hd.head_idx, cur_hd.refcnt + 1};
-        head_acquired = m_old_head.compare_exchange_strong(cur_hd, new_hd);
-      } else if (m_head.load().head_idx == target_head) {
-        cur_hd = m_head.load();
-        cur_hd.head_idx = target_head;
-        new_hd = {cur_hd.head_idx, cur_hd.refcnt + 1};
-        head_acquired = m_head.compare_exchange_strong(cur_hd, new_hd);
-      }
-    } while (!head_acquired);
-
-    return new_hd.head_idx;
-  }
 
   void set_low_watermark(size_t lwm) {
     assert(lwm < m_hwm);
@@ -234,8 +197,90 @@ public:
     return m_cap - (m_tail.load() - m_old_head.load().head_idx);
   }
 
+  size_t debug_get_old_head() const {
+    return m_old_head.load().head_idx;
+  }
+
+  size_t debug_get_head() const {
+    return m_head.load().head_idx;
+  }
+
+  bool take_head_reference(size_t target_head) {
+    buffer_head cur_hd, new_hd;
+    bool head_acquired = false;
+
+    do {
+      if (m_old_head.load().head_idx == target_head) {
+        cur_hd = m_old_head.load();
+        cur_hd.head_idx = target_head;
+        new_hd = {cur_hd.head_idx, cur_hd.refcnt + 1};
+        head_acquired = m_old_head.compare_exchange_strong(cur_hd, new_hd);
+      } else if (m_head.load().head_idx == target_head) {
+        cur_hd = m_head.load();
+        cur_hd.head_idx = target_head;
+        new_hd = {cur_hd.head_idx, cur_hd.refcnt + 1};
+        head_acquired = m_head.compare_exchange_strong(cur_hd, new_hd);
+      }
+    } while (!head_acquired);
+
+    return head_acquired;
+  }
+  
+  bool release_head_reference(size_t head) {
+    buffer_head cur_hd, new_hd;
+    bool head_released = false;
+    do {
+      if (m_old_head.load().head_idx == head) {
+        cur_hd = m_old_head;
+
+        assert(cur_hd.refcnt > 0);
+        new_hd = {cur_hd.head_idx, cur_hd.refcnt - 1};
+        head_released = m_old_head.compare_exchange_strong(cur_hd, new_hd);
+      } else {
+        cur_hd = m_head;
+
+        /* it's possible the head got pushed from current to old */
+        if (cur_hd.head_idx == head) {
+          assert(cur_hd.refcnt > 0);
+          new_hd = {cur_hd.head_idx, cur_hd.refcnt - 1};
+          head_released = m_head.compare_exchange_strong(cur_hd, new_hd);
+        }
+      }
+      _mm_pause();
+    } while (!head_released);
+
+    return head_released;
+  }
+
 private:
-  int64_t try_advance_tail() {
+  /*
+   * FIXME: If target_head does not match *either* the old_head or the
+   * current_head, this routine will loop infinitely.
+   */
+  size_t get_head(size_t target_head) {
+    buffer_head cur_hd, new_hd;
+    bool head_acquired = false;
+
+
+    //fprintf(stderr, "[I]: getting head %ld %ld %ld\n", target_head, m_old_head.load().head_idx, m_head.load().head_idx);
+    do {
+      if (m_old_head.load().head_idx == target_head) {
+        cur_hd = m_old_head.load();
+        cur_hd.head_idx = target_head;
+        new_hd = {cur_hd.head_idx, cur_hd.refcnt + 1};
+        head_acquired = m_old_head.compare_exchange_strong(cur_hd, new_hd);
+      } else if (m_head.load().head_idx == target_head) {
+        cur_hd = m_head.load();
+        cur_hd.head_idx = target_head;
+        new_hd = {cur_hd.head_idx, cur_hd.refcnt + 1};
+        head_acquired = m_head.compare_exchange_strong(cur_hd, new_hd);
+      }
+    } while (!head_acquired);
+
+    return new_hd.head_idx;
+  }
+  
+  ssize_t try_advance_tail() {
     size_t old_value = m_tail.load();
 
     /* if full, fail to advance the tail */
@@ -257,33 +302,6 @@ private:
 
   size_t to_idx(size_t i, size_t head) { return (head + i) % m_cap; }
 
-  static void release_head_reference(void *buff, size_t head) {
-    MutableBuffer<R> *buffer = (MutableBuffer<R> *)buff;
-
-    buffer_head cur_hd, new_hd;
-    do {
-      if (buffer->m_old_head.load().head_idx == head) {
-        cur_hd = buffer->m_old_head;
-        if (cur_hd.refcnt == 0)
-          continue;
-        new_hd = {cur_hd.head_idx, cur_hd.refcnt - 1};
-        if (buffer->m_old_head.compare_exchange_strong(cur_hd, new_hd)) {
-          break;
-        }
-      } else {
-        cur_hd = buffer->m_head;
-        if (cur_hd.refcnt == 0)
-          continue;
-        new_hd = {cur_hd.head_idx, cur_hd.refcnt - 1};
-
-        if (buffer->m_head.compare_exchange_strong(cur_hd, new_hd)) {
-          break;
-        }
-      }
-      _mm_pause();
-    } while (true);
-  }
-
   size_t m_lwm;
   size_t m_hwm;
   size_t m_cap;