use same logic for all platforms for locking and unlocking the file

CHANGELOG.md

@@ -3,7 +3,7 @@
 ### Enhancements
 * <New feature description> (PR [#????](https://github.com/realm/realm-core/pull/????))
 * Add a distinct error code for timeouts (SyncConnectTimeout) rather than using the same one as for less transient failures ([PR #6932](https://github.com/realm/realm-core/pull/6932)).
-* Throw an exception if `File::unlock` has failed, in order to inform the SDK that we are likely hitting some limitation on the OS filesystem, instead of crashing  the application.([PR #6926](https://github.com/realm/realm-core/pull/6926))
+* Throw an exception if `File::unlock` has failed, in order to inform the SDK that we are likely hitting some limitation on the OS filesystem, instead of crashing  the application and use the same file locking logic for all the platforms.([PR #6926](https://github.com/realm/realm-core/pull/6926))
 
 
 ### Fixed

src/realm/util/file.cpp

@@ -507,6 +507,7 @@ void File::open_internal(const std::string& path, AccessMode a, CreateMode c, in
     int fd = ::open(path.c_str(), flags2, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
     if (0 <= fd) {
         m_fd = fd;
+        m_have_lock = false;
         if (success)
             *success = true;
         return;
@@ -562,7 +563,8 @@ void File::close() noexcept
 
     if (m_fd < 0)
         return;
-    unlock();
+    if (m_have_lock)
+        unlock();
     int r = ::close(m_fd);
     REALM_ASSERT_RELEASE(r == 0);
     m_fd = -1;
@@ -1212,9 +1214,9 @@ bool File::rw_lock(bool exclusive, bool non_blocking)
 bool File::lock(bool exclusive, bool non_blocking)
 {
     REALM_ASSERT_RELEASE(is_attached());
+    REALM_ASSERT_RELEASE(!m_have_lock);
 
 #ifdef _WIN32 // Windows version
-    REALM_ASSERT_RELEASE(!m_have_lock);
 
     // Under Windows a file lock must be explicitely released before
     // the file is closed. It will eventually be released by the
@@ -1259,8 +1261,10 @@ bool File::lock(bool exclusive, bool non_blocking)
     if (non_blocking)
         operation |= LOCK_NB;
     do {
-        if (flock(m_fd, operation) == 0)
+        if (flock(m_fd, operation) == 0) {
+            m_have_lock = true;
             return true;
+        }
     } while (errno == EINTR);
     int err = errno; // Eliminate any risk of clobbering
     if (err == EWOULDBLOCK)
@@ -1271,10 +1275,10 @@ bool File::lock(bool exclusive, bool non_blocking)
 
 void File::unlock() noexcept
 {
-#ifdef _WIN32 // Windows version
     if (!m_have_lock)
         return;
 
+#ifdef _WIN32 // Windows version
     OVERLAPPED overlapped;
     overlapped.hEvent = 0;
     overlapped.OffsetHigh = 0;
@@ -1285,11 +1289,8 @@ void File::unlock() noexcept
     REALM_ASSERT_RELEASE(r);
     m_have_lock = false;
 #else
-    // The Linux man page for flock() does not state explicitely that
-    // unlocking is idempotent, however, we will assume it since there
-    // is no mention of the error that would be reported if a
-    // non-locked file were unlocked.
     _unlock(m_fd);
+    m_have_lock = false;
 #endif
 }
 

src/realm/util/file.hpp

@@ -627,9 +627,9 @@ class File {
     class Streambuf;
 
 private:
+    bool m_have_lock = false; // Only valid when m_fd is not null
 #ifdef _WIN32
     HANDLE m_fd = nullptr;
-    bool m_have_lock = false; // Only valid when m_fd is not null
 #else
     int m_fd = -1;
 #ifdef REALM_FILELOCK_EMULATION
@@ -983,9 +983,12 @@ inline File::File(File&& f) noexcept
 #ifdef _WIN32
     m_fd = f.m_fd;
     m_have_lock = f.m_have_lock;
+    f.m_have_lock = false;
     f.m_fd = nullptr;
 #else
     m_fd = f.m_fd;
+    m_have_lock = f.m_have_lock;
+    f.m_have_lock = false;
 #ifdef REALM_FILELOCK_EMULATION
     m_pipe_fd = f.m_pipe_fd;
     m_has_exclusive_lock = f.m_has_exclusive_lock;
@@ -1003,10 +1006,13 @@ inline File& File::operator=(File&& f) noexcept
 #ifdef _WIN32
     m_fd = f.m_fd;
     m_have_lock = f.m_have_lock;
+    f.m_have_lock = false;
     f.m_fd = nullptr;
 #else
     m_fd = f.m_fd;
     f.m_fd = -1;
+    m_have_lock = f.m_have_lock;
+    f.m_have_lock = false;
 #ifdef REALM_FILELOCK_EMULATION
     m_pipe_fd = f.m_pipe_fd;
     f.m_pipe_fd = -1;