From 203238f7e5be9c21b5e6d330d24297b4cd5024b4 Mon Sep 17 00:00:00 2001
From: Hongze Cheng <hzcheng@taosdata.com>
Date: Mon, 22 Jun 2020 18:15:35 +0800
Subject: [PATCH] implement read-write spin latch

---
 src/tsdb/inc/tsdbMain.h |  2 ++
 src/util/inc/trwlatch.h | 36 +++++++++++++++++++
 src/util/src/trwlatch.c | 80 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 118 insertions(+)
 create mode 100644 src/util/inc/trwlatch.h
 create mode 100644 src/util/src/trwlatch.c

diff --git a/src/tsdb/inc/tsdbMain.h b/src/tsdb/inc/tsdbMain.h
index cd64e48347..7365d7b151 100644
--- a/src/tsdb/inc/tsdbMain.h
+++ b/src/tsdb/inc/tsdbMain.h
@@ -25,6 +25,7 @@
 #include "tsdb.h"
 #include "tskiplist.h"
 #include "tutil.h"
+#include "trwlatch.h"
 
 #ifdef __cplusplus
 extern "C" {
@@ -59,6 +60,7 @@ typedef struct STable {
   TSKEY          lastKey;        // lastkey inserted in this table, initialized as 0, TODO: make a structure
   char*          sql;
   void*          cqhandle;
+  SRWLatch       latch;  // TODO: implementa latch functions
   T_REF_DECLARE();
 } STable;
 
diff --git a/src/util/inc/trwlatch.h b/src/util/inc/trwlatch.h
new file mode 100644
index 0000000000..c6923f0e90
--- /dev/null
+++ b/src/util/inc/trwlatch.h
@@ -0,0 +1,36 @@
+/*
+ * Copyright (c) 2019 TAOS Data, Inc. <jhtao@taosdata.com>
+ *
+ * This program is free software: you can use, redistribute, and/or modify
+ * it under the terms of the GNU Affero General Public License, version 3
+ * or later ("AGPL"), as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+#ifndef __TD_RWLATCH_H__
+#define __TD_RWLATCH_H__
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <stdint.h>
+
+typedef int32_t SRWLatch;
+
+void taosInitRWLatch(SRWLatch *pLatch);
+void taosWLockLatch(SRWLatch *pLatch);
+void taosWUnLockLatch(SRWLatch *pLatch);
+void taosRLockLatch(SRWLatch *pLatch);
+void taosRUnLockLatch(SRWLatch *pLatch);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
diff --git a/src/util/src/trwlatch.c b/src/util/src/trwlatch.c
new file mode 100644
index 0000000000..cc027aa3df
--- /dev/null
+++ b/src/util/src/trwlatch.c
@@ -0,0 +1,80 @@
+/*
+ * Copyright (c) 2019 TAOS Data, Inc. <jhtao@taosdata.com>
+ *
+ * This program is free software: you can use, redistribute, and/or modify
+ * it under the terms of the GNU Affero General Public License, version 3
+ * or later ("AGPL"), as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+// #define _GNU_SOURCE
+// #include <pthread.h>
+
+#include "trwlatch.h"
+#include "os.h"
+
+#define TD_RWLATCH_WRITE_FLAG 0x40000000
+
+void taosInitRWLatch(SRWLatch *pLatch) { *pLatch = 0; }
+
+void taosWLockLatch(SRWLatch *pLatch) {
+  SRWLatch oLatch, nLatch;
+  int      nLoops = 0;
+
+  // Set write flag
+  while (1) {
+    oLatch = atomic_load_32(pLatch);
+    if (oLatch & TD_RWLATCH_WRITE_FLAG) {
+      nLoops++;
+      if (nLoops > 1000) {
+        sched_yield();
+        nLoops = 0;
+      }
+      continue;
+    }
+
+    nLatch = oLatch | TD_RWLATCH_WRITE_FLAG;
+    if (atomic_val_compare_exchange_32(pLatch, oLatch, nLatch) == oLatch) break;
+  }
+
+  // wait for all reads end
+  nLoops = 0;
+  while (1) {
+    oLatch = atomic_load_32(pLatch);
+    if (oLatch == TD_RWLATCH_WRITE_FLAG) break;
+    nLoops++;
+    if (nLoops > 1000) {
+      sched_yield();
+      nLoops = 0;
+    }
+  }
+}
+
+void taosWUnLockLatch(SRWLatch *pLatch) { atomic_store_32(pLatch, 0); }
+
+void taosRLockLatch(SRWLatch *pLatch) {
+  SRWLatch oLatch, nLatch;
+  int      nLoops = 0;
+
+  while (1) {
+    oLatch = atomic_load_32(pLatch);
+    if (oLatch & TD_RWLATCH_WRITE_FLAG) {
+      nLoops++;
+      if (nLoops > 1000) {
+        sched_yield();
+        nLoops = 0;
+      }
+      continue;
+    }
+
+    nLatch = oLatch + 1;
+    if (atomic_val_compare_exchange_32(pLatch, oLatch, nLatch) == oLatch) break;
+  }
+}
+
+void taosRUnLockLatch(SRWLatch *pLatch) { atomic_fetch_sub_32(pLatch, 1); }
\ No newline at end of file
-- 
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