From c2fe0a71bc6a2dae861d84e8a986fe57834c38b6 Mon Sep 17 00:00:00 2001
From: Leo Yuriev <leo@yuriev.ru>
Date: Sun, 14 Jan 2018 19:48:07 +0300
Subject: [PATCH] mdbx-windows: reserve address space to avoid occupy it by
 other threads.

Change-Id: Ia5caec6bbeb55c7894de70e349e6e9479572b688
---
 src/osal.c | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/src/osal.c b/src/osal.c
index b47d342a..2b5791e4 100644
--- a/src/osal.c
+++ b/src/osal.c
@@ -970,7 +970,7 @@ int mdbx_mresize(int flags, mdbx_mmap_t *map, size_t size, size_t limit) {
   }
 
   /* Windows unable:
-    *  - shrinking a mapped file;
+    *  - shrink a mapped file;
     *  - change size of mapped view;
     *  - extend read-only mapping;
     * Therefore we should unmap/map entire section. */
@@ -979,6 +979,8 @@ int mdbx_mresize(int flags, mdbx_mmap_t *map, size_t size, size_t limit) {
     return ntstatus2errcode(status);
   status = NtClose(map->section);
   map->section = NULL;
+  PVOID ReservedAddress = NULL;
+  SIZE_T ReservedSize = limit;
 
   if (!NT_SUCCESS(status)) {
   bailout_ntstatus:
@@ -986,9 +988,27 @@ int mdbx_mresize(int flags, mdbx_mmap_t *map, size_t size, size_t limit) {
   bailout:
     map->address = NULL;
     map->current = map->length = 0;
+    if (ReservedAddress)
+      (void)NtFreeVirtualMemory(GetCurrentProcess(), &ReservedAddress,
+                                &ReservedSize, MEM_RELEASE);
     return err;
   }
 
+  /* resizing of the file may take a while,
+   * therefore we reserve address space to avoid occupy it by other threads */
+  ReservedAddress = map->address;
+  status = NtAllocateVirtualMemory(GetCurrentProcess(), &ReservedAddress, 0,
+                                   &ReservedSize, MEM_RESERVE, PAGE_NOACCESS);
+  if (!NT_SUCCESS(status)) {
+    ReservedAddress = NULL;
+    if (status != /* STATUS_CONFLICTING_ADDRESSES */ 0xC0000018 ||
+        limit == map->length)
+      goto bailout_ntstatus /* no way to recovery */;
+
+    /* assume we can change base address if mapping size changed */
+    map->address = NULL;
+  }
+
 retry_file_and_section:
   err = mdbx_filesize(map->fd, &map->filesize);
   if (err != MDBX_SUCCESS)
@@ -1018,6 +1038,15 @@ retry_file_and_section:
   if (!NT_SUCCESS(status))
     goto bailout_ntstatus;
 
+  if (ReservedAddress) {
+    /* release reserved address space */
+    status = NtFreeVirtualMemory(GetCurrentProcess(), &ReservedAddress,
+                                 &ReservedSize, MEM_RELEASE);
+    ReservedAddress = NULL;
+    if (!NT_SUCCESS(status))
+      goto bailout_ntstatus;
+  }
+
 retry_mapview:;
   SIZE_T ViewSize = (flags & MDBX_RDONLY) ? size : limit;
   status = NtMapViewOfSection(