SERVER-7378 Prevent WRITETODATAFILES and FlushViewOfFile from running at the same time

Prevent errors on Azure Storage drives that occur when a memory-mapped
data file is modified in memory while it is being flushed to disk with
FlushViewOfFile.  Use a SimpleMutex (Critical Section on Windows) to
prevent these two routines from running at the same time.

2 files changed, 16 insertions, 4 deletions

diff --git a/src/mongo/db/dur_writetodatafiles.cpp b/src/mongo/db/dur_writetodatafiles.cpp
index a8cda0e6506..f6978920e14 100644
--- a/src/mongo/db/dur_writetodatafiles.cpp
+++ b/src/mongo/db/dur_writetodatafiles.cpp
@@ -17,12 +17,17 @@
 */
 
 #include "pch.h"
-#include "dur_commitjob.h"
-#include "dur_stats.h"
-#include "dur_recover.h"
-#include "../util/timer.h"
+
+#include "mongo/db/dur_commitjob.h"
+#include "mongo/db/dur_recover.h"
+#include "mongo/db/dur_stats.h"
+#include "mongo/util/concurrency/mutex.h"
+#include "mongo/util/timer.h"
 
 namespace mongo {
+#ifdef _WIN32
+    extern SimpleMutex globalFlushMutex; // defined in mongo/util/mmap_win.cpp
+#endif
     namespace dur {
 
         void debugValidateAllMapsMatch();
@@ -82,6 +87,9 @@ namespace mongo {
         */
 
         void WRITETODATAFILES(const JSectHeader& h, AlignedBuilder& uncompressed) {
+#ifdef _WIN32
+            SimpleMutex::scoped_lock _globalFlushMutex(globalFlushMutex);
+#endif
             Timer t;
             WRITETODATAFILES_Impl1(h, uncompressed);
             unsigned long long m = t.micros();
diff --git a/src/mongo/util/mmap_win.cpp b/src/mongo/util/mmap_win.cpp
index 50936f637de..27a0911cc54 100644
--- a/src/mongo/util/mmap_win.cpp
+++ b/src/mongo/util/mmap_win.cpp
@@ -326,6 +326,9 @@ namespace mongo {
         return newPrivateView;
     }
 
+    // prevent WRITETODATAFILES() from running at the same time as FlushViewOfFile()
+    SimpleMutex globalFlushMutex("globalFlushMutex");
+
     class WindowsFlushable : public MemoryMappedFile::Flushable {
     public:
         WindowsFlushable( void * view,
@@ -339,6 +342,7 @@ namespace mongo {
             if (!_view || !_fd)
                 return;
 
+            SimpleMutex::scoped_lock _globalFlushMutex(globalFlushMutex);
             scoped_lock lk(*_flushMutex);
 
             int loopCount = 0;