From 5cfec7a83205b2ef9a7f9409c742ba047f8bc7a0 Mon Sep 17 00:00:00 2001
From: Leo Yuriev <leo@yuriev.ru>
Date: Wed, 31 Jan 2018 15:15:54 +0300
Subject: [PATCH] mdbx: workaround for Windows LockFileEx/WriteFile bug.

This resolves https://github.com/leo-yuriev/libmdbx/issues/25
---
 src/bits.h        |  2 ++
 src/lck-windows.c | 12 +++++++++++-
 src/mdbx.c        |  9 +++++++++
 3 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/src/bits.h b/src/bits.h
index 293de7f8..1d39d060 100644
--- a/src/bits.h
+++ b/src/bits.h
@@ -743,6 +743,8 @@ struct MDBX_env {
 
 #if defined(_WIN32) || defined(_WIN64)
   SRWLOCK me_remap_guard;
+  /* Workaround for LockFileEx and WriteFile multithread bug */
+  CRITICAL_SECTION me_windowsbug_lock;
 #else
   mdbx_fastmutex_t me_remap_guard;
 #endif
diff --git a/src/lck-windows.c b/src/lck-windows.c
index c7ce8a17..02dc9b46 100644
--- a/src/lck-windows.c
+++ b/src/lck-windows.c
@@ -127,16 +127,26 @@ static __inline BOOL funlock(mdbx_filehandle_t fd, uint64_t offset,
 #define LCK_WHOLE 0, LCK_MAXLEN
 
 int mdbx_txn_lock(MDBX_env *env, bool dontwait) {
+  if (dontwait) {
+    if (!TryEnterCriticalSection(&env->me_windowsbug_lock))
+      return MDBX_BUSY;
+  } else {
+    EnterCriticalSection(&env->me_windowsbug_lock);
+  }
+
   if (flock(env->me_fd, dontwait ? (LCK_EXCLUSIVE | LCK_DONTWAIT)
                                  : (LCK_EXCLUSIVE | LCK_WAITFOR),
             LCK_BODY))
     return MDBX_SUCCESS;
   int rc = GetLastError();
+  LeaveCriticalSection(&env->me_windowsbug_lock);
   return (!dontwait || rc != ERROR_LOCK_VIOLATION) ? rc : MDBX_BUSY;
 }
 
 void mdbx_txn_unlock(MDBX_env *env) {
-  if (!funlock(env->me_fd, LCK_BODY))
+  int rc = funlock(env->me_fd, LCK_BODY);
+  LeaveCriticalSection(&env->me_windowsbug_lock);
+  if (!rc)
     mdbx_panic("%s failed: errcode %u", mdbx_func_, GetLastError());
 }
 
diff --git a/src/mdbx.c b/src/mdbx.c
index 60569ca8..f174bc2c 100644
--- a/src/mdbx.c
+++ b/src/mdbx.c
@@ -4450,6 +4450,7 @@ int __cold mdbx_env_create(MDBX_env **penv) {
 
 #if defined(_WIN32) || defined(_WIN64)
   InitializeSRWLock(&env->me_remap_guard);
+  InitializeCriticalSection(&env->me_windowsbug_lock);
 #else
   rc = mdbx_fastmutex_init(&env->me_remap_guard);
   if (unlikely(rc != MDBX_SUCCESS)) {
@@ -5487,6 +5488,14 @@ int __cold mdbx_env_close_ex(MDBX_env *env, int dont_sync) {
 
   mdbx_env_close0(env);
   mdbx_ensure(env, mdbx_fastmutex_destroy(&env->me_dbi_lock) == MDBX_SUCCESS);
+#if defined(_WIN32) || defined(_WIN64)
+  /* me_remap_guard don't have destructor (Slim Reader/Writer Lock) */
+  DeleteCriticalSection(&env->me_windowsbug_lock);
+#else
+  mdbx_ensure(env,
+              mdbx_fastmutex_destroy(&env->me_remap_guard) == MDBX_SUCCESS);
+#endif /* Windows */
+
   env->me_signature = 0;
   free(env);