Add debug check function LWLockHeldByMeInMode()

Tests whether my process holds a lock in given mode.
Add initial usage in MarkBufferDirty().

Thomas Munro

src/backend/storage/buffer/bufmgr.c

@@ -1460,8 +1460,8 @@ MarkBufferDirty(Buffer buffer)
 	bufHdr = GetBufferDescriptor(buffer - 1);
 
 	Assert(BufferIsPinned(buffer));
-	/* unfortunately we can't check if the lock is held exclusively */
-	Assert(LWLockHeldByMe(BufferDescriptorGetContentLock(bufHdr)));
+	Assert(LWLockHeldByMeInMode(BufferDescriptorGetContentLock(bufHdr),
+								LW_EXCLUSIVE));
 
 	old_buf_state = pg_atomic_read_u32(&bufHdr->state);
 	for (;;)

src/backend/storage/lmgr/lwlock.c

@@ -1880,10 +1880,9 @@ LWLockReleaseAll(void)
 
 
 /*
- * LWLockHeldByMe - test whether my process currently holds a lock
+ * LWLockHeldByMe - test whether my process holds a lock in any mode
  *
- * This is meant as debug support only.  We currently do not distinguish
- * whether the lock is held shared or exclusive.
+ * This is meant as debug support only.
  */
 bool
 LWLockHeldByMe(LWLock *l)
@@ -1897,3 +1896,21 @@ LWLockHeldByMe(LWLock *l)
 	}
 	return false;
 }
+
+/*
+ * LWLockHeldByMeInMode - test whether my process holds a lock in given mode
+ *
+ * This is meant as debug support only.
+ */
+bool
+LWLockHeldByMeInMode(LWLock *l, LWLockMode mode)
+{
+	int			i;
+
+	for (i = 0; i < num_held_lwlocks; i++)
+	{
+		if (held_lwlocks[i].lock == l && held_lwlocks[i].mode == mode)
+			return true;
+	}
+	return false;
+}

src/include/storage/lwlock.h

@@ -175,6 +175,7 @@ extern void LWLockRelease(LWLock *lock);
 extern void LWLockReleaseClearVar(LWLock *lock, uint64 *valptr, uint64 val);
 extern void LWLockReleaseAll(void);
 extern bool LWLockHeldByMe(LWLock *lock);
+extern bool LWLockHeldByMeInMode(LWLock *lock, LWLockMode mode);
 
 extern bool LWLockWaitForVar(LWLock *lock, uint64 *valptr, uint64 oldval, uint64 *newval);
 extern void LWLockUpdateVar(LWLock *lock, uint64 *valptr, uint64 value);