Merge pull request #28984 from vespa-engine/balder/make-cached-size-atomic

Since the cached size can be updated by many threads, it must be an a…

2 files changed, 17 insertions, 13 deletions

diff --git a/vespalib/src/vespa/fastos/linux_file.cpp b/vespalib/src/vespa/fastos/linux_file.cpp
index b6094a050d9..0f32aa953a8 100644
--- a/vespalib/src/vespa/fastos/linux_file.cpp
+++ b/vespalib/src/vespa/fastos/linux_file.cpp
@@ -202,7 +202,7 @@ FastOS_Linux_File::Write2(const void *buffer, size_t length)
         if (writtenNow > 0) {
             written += writtenNow;
         } else {
-            return (written > 0) ? written : writtenNow;;
+            return (written > 0) ? written : writtenNow;
         }
     }
     return written;
@@ -239,8 +239,8 @@ FastOS_Linux_File::internalWrite2(const void *buffer, size_t length)
         }
         if (writeRes > 0) {
             _filePointer += writeRes;
-            if (_filePointer > _cachedSize) {
-                _cachedSize = _filePointer;
+            if (_filePointer > _cachedSize.load(std::memory_order_relaxed)) {
+                _cachedSize.store(_filePointer, std::memory_order_relaxed);
             }
         }
     } else {
@@ -277,7 +277,7 @@ FastOS_Linux_File::SetSize(int64_t newSize)
     bool rc = FastOS_UNIX_File::SetSize(newSize);
 
     if (rc) {
-        _cachedSize = newSize;
+        _cachedSize.store(newSize, std::memory_order_relaxed);
     }
     return rc;
 }
@@ -334,19 +334,21 @@ FastOS_Linux_File::DirectIOPadding (int64_t offset, size_t length, size_t &padBe
         if (padAfter == _directIOFileAlign) {
             padAfter = 0;
         }
-        if (int64_t(offset+length+padAfter) > _cachedSize) {
+        int64_t fileSize = _cachedSize.load(std::memory_order_relaxed);
+        if (int64_t(offset+length+padAfter) > fileSize) {
             // _cachedSize is not really trustworthy, so if we suspect it is not correct, we correct it.
             // The main reason is that it will not reflect the file being extended by another filedescriptor.
-            _cachedSize = getSize();
+            fileSize = getSize();
+            _cachedSize.store(fileSize, std::memory_order_relaxed);
         }
         if ((padAfter != 0) &&
-            (static_cast<int64_t>(offset + length + padAfter) > _cachedSize) &&
-            (static_cast<int64_t>(offset + length) <= _cachedSize))
+            (static_cast<int64_t>(offset + length + padAfter) > fileSize) &&
+            (static_cast<int64_t>(offset + length) <= fileSize))
         {
-            padAfter = _cachedSize - (offset + length);
+            padAfter = fileSize - (offset + length);
         }
 
-        if (static_cast<uint64_t>(offset + length + padAfter) <= static_cast<uint64_t>(_cachedSize)) {
+        if (static_cast<uint64_t>(offset + length + padAfter) <= static_cast<uint64_t>(fileSize)) {
             return true;
         }
     }
diff --git a/vespalib/src/vespa/fastos/linux_file.h b/vespalib/src/vespa/fastos/linux_file.h
index 1295ce38316..af6e6af51af 100644
--- a/vespalib/src/vespa/fastos/linux_file.h
+++ b/vespalib/src/vespa/fastos/linux_file.h
@@ -10,21 +10,23 @@
 #pragma once
 
 #include "unix_file.h"
+#include <atomic>
 
 /**
  * This is the Linux implementation of @ref FastOS_File. Most
  * methods are inherited from @ref FastOS_UNIX_File.
  */
-class FastOS_Linux_File : public FastOS_UNIX_File
+class FastOS_Linux_File final : public FastOS_UNIX_File
 {
 public:
     using FastOS_UNIX_File::ReadBuf;
 protected:
-    int64_t _cachedSize;
+    std::atomic<int64_t> _cachedSize;
     int64_t _filePointer;   // Only maintained/used in directio mode
 
 public:
-    FastOS_Linux_File (const char *filename = nullptr);
+    FastOS_Linux_File() : FastOS_Linux_File(nullptr) {}
+    explicit FastOS_Linux_File(const char *filename);
     ~FastOS_Linux_File () override;
     bool GetDirectIORestrictions(size_t &memoryAlignment, size_t &transferGranularity, size_t &transferMaximum) override;
     bool DirectIOPadding(int64_t offset, size_t length, size_t &padBefore, size_t &padAfter) override;