flush OS write buffers before saving control file

This ensures that pieces are physically written to disk before
marking them as finished in the control file.

This should prevent data loss and corruption when resuming downloads
after a system crash.

Signed-off-by: Ali MJ Al-Nasrawy <alimjalnasrawy@gmail.com>

src/AbstractDiskWriter.cc

@@ -590,4 +590,16 @@ void AbstractDiskWriter::dropCache(int64_t len, int64_t offset)
 #endif // HAVE_POSIX_FADVISE
 }
 
+void AbstractDiskWriter::flushOSBuffers()
+{
+  if (fd_ == A2_BAD_FD) {
+    return;
+  }
+#ifdef __MINGW32__
+  FlushFileBuffers(fd_);
+#else // !__MINGW32__
+  fsync(fd_);
+#endif // __MINGW32__
+}
+
 } // namespace aria2

src/AbstractDiskWriter.h

@@ -100,6 +100,8 @@ public:
   virtual void enableMmap() CXX11_OVERRIDE;
 
   virtual void dropCache(int64_t len, int64_t offset) CXX11_OVERRIDE;
+
+  virtual void flushOSBuffers() CXX11_OVERRIDE;
 };
 
 } // namespace aria2

src/AbstractSingleDiskAdaptor.cc

@@ -103,6 +103,11 @@ void AbstractSingleDiskAdaptor::writeCache(const WrDiskCacheEntry* entry)
   }
 }
 
+void AbstractSingleDiskAdaptor::flushOSBuffers()
+{
+  diskWriter_->flushOSBuffers();
+}
+
 bool AbstractSingleDiskAdaptor::fileExists()
 {
   return File(getFilePath()).exists();

src/AbstractSingleDiskAdaptor.h

@@ -72,6 +72,8 @@ public:
 
   virtual void writeCache(const WrDiskCacheEntry* entry) CXX11_OVERRIDE;
 
+  virtual void flushOSBuffers() CXX11_OVERRIDE;
+
   virtual bool fileExists() CXX11_OVERRIDE;
 
   virtual int64_t size() CXX11_OVERRIDE;

src/DiskAdaptor.h

@@ -114,6 +114,9 @@ public:
   // Writes cached data to the underlying disk.
   virtual void writeCache(const WrDiskCacheEntry* entry) = 0;
 
+  // Force physical write of data from OS buffer cache.
+  virtual void flushOSBuffers() {};
+
   void setFileAllocationMethod(FileAllocationMethod method)
   {
     fileAllocationMethod_ = method;

src/DiskWriter.h

@@ -85,6 +85,9 @@ public:
 
   // Drops cache in range [offset, offset + len)
   virtual void dropCache(int64_t len, int64_t offset) {}
+
+  // Force physical write of data from OS buffer cache.
+  virtual void flushOSBuffers() {}
 };
 
 } // namespace aria2

src/MultiDiskAdaptor.cc

@@ -419,6 +419,17 @@ void MultiDiskAdaptor::writeCache(const WrDiskCacheEntry* entry)
   }
 }
 
+void MultiDiskAdaptor::flushOSBuffers()
+{
+  for (auto& dwent : openedDiskWriterEntries_) {
+    auto& dw = dwent->getDiskWriter();
+    if (!dw) {
+      continue;
+    }
+    dw->flushOSBuffers();
+  }
+}
+
 bool MultiDiskAdaptor::fileExists()
 {
   return std::find_if(std::begin(getFileEntries()), std::end(getFileEntries()),

src/MultiDiskAdaptor.h

@@ -135,6 +135,8 @@ public:
 
   virtual void writeCache(const WrDiskCacheEntry* entry) CXX11_OVERRIDE;
 
+  virtual void flushOSBuffers() CXX11_OVERRIDE;
+
   virtual bool fileExists() CXX11_OVERRIDE;
 
   virtual int64_t size() CXX11_OVERRIDE;

src/RequestGroup.cc

@@ -211,6 +211,7 @@ void RequestGroup::closeFile()
 {
   if (pieceStorage_) {
     pieceStorage_->flushWrDiskCacheEntry(true);
+    pieceStorage_->getDiskAdaptor()->flushOSBuffers();
     pieceStorage_->getDiskAdaptor()->closeFile();
   }
 }
@@ -1292,6 +1293,7 @@ void RequestGroup::saveControlFile() const
   if (saveControlFile_) {
     if (pieceStorage_) {
       pieceStorage_->flushWrDiskCacheEntry(false);
+      pieceStorage_->getDiskAdaptor()->flushOSBuffers();
     }
     progressInfoFile_->save();
   }