From a2bdbc97dc2f1d9e7a512d45bef68846bb22a722 Mon Sep 17 00:00:00 2001
From: Leonid Yuriev <leo@yuriev.ru>
Date: Wed, 20 May 2020 13:31:04 +0300
Subject: [PATCH] mdbx: truncate clk-file when DB closed in sync-state.

Change-Id: I2e2438606118e3aa3fa9d60811fea99994403d32
---
 src/lck-posix.c   |   4 +-
 src/lck-windows.c | 101 ++++++++++++++++++++++++++++++++--------------
 2 files changed, 73 insertions(+), 32 deletions(-)

diff --git a/src/lck-posix.c b/src/lck-posix.c
index 6b6127bd..9038739f 100644
--- a/src/lck-posix.c
+++ b/src/lck-posix.c
@@ -477,8 +477,10 @@ MDBX_INTERNAL_FUNC int __cold mdbx_lck_destroy(MDBX_env *env,
 
     mdbx_assert(env, rc == 0);
     if (rc == 0) {
+      const bool synced = env->me_lck_mmap.lck->mti_unsynced_pages == 0;
       mdbx_munmap(&env->me_lck_mmap);
-      rc = ftruncate(env->me_lfd, 0) ? errno : 0;
+      if (synced)
+        rc = ftruncate(env->me_lfd, 0) ? errno : 0;
     }
 
     mdbx_jitter4testing(false);
diff --git a/src/lck-windows.c b/src/lck-windows.c
index cb9fc1d7..8ec4659a 100644
--- a/src/lck-windows.c
+++ b/src/lck-windows.c
@@ -344,13 +344,6 @@ mdbx_resume_threads_after_remap(mdbx_handle_array_t *array) {
  *    i.e. free/shared/exclusive x free/shared/exclusive == 9.
  *    Only 6 states of FSM are used, which 2 of ones are transitive.
  *
- *  The mdbx_lck_seize() moves the locking-FSM from the initial free/unlocked
- *  state to the "exclusive write" (and returns MDBX_RESULT_TRUE) if possible,
- *  or to the "used" (and returns MDBX_RESULT_FALSE).
- *
- *  The mdbx_lck_downgrade() moves the locking-FSM from "exclusive write"
- *  state to the "used" (i.e. shared) state.
- *
  * States:
  *   ?-?  = free, i.e. unlocked
  *   S-?  = used, i.e. shared lock
@@ -361,6 +354,16 @@ mdbx_resume_threads_after_remap(mdbx_handle_array_t *array) {
  *   S-E  = locked (transitive state)
  *   E-S
  *   E-E  = exclusive-write, i.e. exclusive due (re)initialization
+ *
+ *  The mdbx_lck_seize() moves the locking-FSM from the initial free/unlocked
+ *  state to the "exclusive write" (and returns MDBX_RESULT_TRUE) if possible,
+ *  or to the "used" (and returns MDBX_RESULT_FALSE).
+ *
+ *  The mdbx_lck_downgrade() moves the locking-FSM from "exclusive write"
+ *  state to the "used" (i.e. shared) state.
+ *
+ *  The mdbx_lck_upgrade() moves the locking-FSM from "used" (i.e. shared)
+ *  state to the "exclusive write" state.
  */
 
 static void lck_unlock(MDBX_env *env) {
@@ -406,30 +409,6 @@ static void lck_unlock(MDBX_env *env) {
   }
 }
 
-MDBX_INTERNAL_FUNC int mdbx_lck_init(MDBX_env *env,
-                                     MDBX_env *inprocess_neighbor,
-                                     int global_uniqueness_flag) {
-  (void)env;
-  (void)inprocess_neighbor;
-  (void)global_uniqueness_flag;
-  return MDBX_SUCCESS;
-}
-
-MDBX_INTERNAL_FUNC int mdbx_lck_destroy(MDBX_env *env,
-                                        MDBX_env *inprocess_neighbor) {
-  (void)inprocess_neighbor;
-
-  /* LY: should unmap before releasing the locks to avoid race condition and
-   * STATUS_USER_MAPPED_FILE/ERROR_USER_MAPPED_FILE */
-  if (env->me_map)
-    mdbx_munmap(&env->me_dxb_mmap);
-  if (env->me_lck)
-    mdbx_munmap(&env->me_lck_mmap);
-
-  lck_unlock(env);
-  return MDBX_SUCCESS;
-}
-
 /* Seize state as 'exclusive-write' (E-E and returns MDBX_RESULT_TRUE)
  * or as 'used' (S-? and returns MDBX_RESULT_FALSE).
  * Oherwise returns an error. */
@@ -553,6 +532,66 @@ MDBX_INTERNAL_FUNC int mdbx_lck_downgrade(MDBX_env *env) {
   return MDBX_SUCCESS /* 5) now at S-? (used), done */;
 }
 
+MDBX_INTERNAL_FUNC int mdbx_lck_upgrade(MDBX_env *env) {
+  /* Transite from used state (S-?) to exclusive-write (E-E) */
+  assert(env->me_lfd != INVALID_HANDLE_VALUE);
+
+  if (env->me_flags & MDBX_EXCLUSIVE)
+    return MDBX_SUCCESS /* nope since files were must be opened non-shareable */
+        ;
+
+  int rc;
+  /* 1) now on S-? (used), try S-E (locked) */
+  mdbx_jitter4testing(false);
+  if (!flock(env->me_lfd, LCK_EXCLUSIVE | LCK_DONTWAIT, LCK_UPPER)) {
+    rc = GetLastError() /* 2) something went wrong, give up */;
+    mdbx_verbose("%s, err %u", "S-?(used) >> S-E(locked)", rc);
+    return rc;
+  }
+
+  /* 3) now on S-E (locked), transite to ?-E (middle) */
+  if (!funlock(env->me_lfd, LCK_LOWER))
+    mdbx_panic("%s(%s) failed: err %u", __func__, "S-E(locked) >> ?-E(middle)",
+               GetLastError());
+
+  /* 4) now on ?-E (middle), try E-E (exclusive-write) */
+  mdbx_jitter4testing(false);
+  if (!flock(env->me_lfd, LCK_EXCLUSIVE | LCK_DONTWAIT, LCK_LOWER)) {
+    rc = GetLastError() /* 5) something went wrong, give up */;
+    mdbx_verbose("%s, err %u", "?-E(middle) >> E-E(exclusive-write)", rc);
+    return rc;
+  }
+
+  return MDBX_SUCCESS /* 6) now at E-E (exclusive-write), done */;
+}
+
+MDBX_INTERNAL_FUNC int mdbx_lck_init(MDBX_env *env,
+                                     MDBX_env *inprocess_neighbor,
+                                     int global_uniqueness_flag) {
+  (void)env;
+  (void)inprocess_neighbor;
+  (void)global_uniqueness_flag;
+  return MDBX_SUCCESS;
+}
+
+MDBX_INTERNAL_FUNC int mdbx_lck_destroy(MDBX_env *env,
+                                        MDBX_env *inprocess_neighbor) {
+  /* LY: should unmap before releasing the locks to avoid race condition and
+   * STATUS_USER_MAPPED_FILE/ERROR_USER_MAPPED_FILE */
+  if (env->me_map)
+    mdbx_munmap(&env->me_dxb_mmap);
+  if (env->me_lck) {
+    const bool synced = env->me_lck_mmap.lck->mti_unsynced_pages == 0;
+    mdbx_munmap(&env->me_lck_mmap);
+    if (synced && !inprocess_neighbor && env->me_lfd != INVALID_HANDLE_VALUE &&
+        mdbx_lck_upgrade(env) == MDBX_SUCCESS)
+      /* this will fail if LCK is used/mmapped by other process(es) */
+      mdbx_ftruncate(env->me_lfd, 0);
+  }
+  lck_unlock(env);
+  return MDBX_SUCCESS;
+}
+
 /*----------------------------------------------------------------------------*/
 /* reader checking (by pid) */