feat: Implemented [SIM] Support Windows-native file locking for SourceMapCache

internal/sourcemap/cache_lock_windows.go

@@ -8,6 +8,19 @@
 import (
 	"fmt"
 	"os"
+
+	"golang.org/x/sys/windows"
+)
+
+const (
+	// LockFileEx flags
+	LOCKFILE_EXCLUSIVE_LOCK   = 0x00000002
+	LOCKFILE_FAIL_IMMEDIATELY = 0x00000001
+)
+
+// Error codes from Windows
+const (
+	ERROR_LOCK_VIOLATION = 0x21
 )
 
 func (sc *SourceCache) acquireLock(entryPath string, exclusive bool) (*os.File, error) {
@@ -16,9 +29,50 @@
 	if err != nil {
 		return nil, fmt.Errorf("failed to open lock file %q: %w", lp, err)
 	}
-	return lf, nil
+
+	// Set the file to not inherit by child processes (Windows best practice for locks)
+	if err := windows.SetHandleInformation(windows.Handle(lf.Fd()), windows.HANDLE_FLAG_INHERIT, 0); err != nil {
+		// Non-fatal, but log warning in production
+	}
+
+	var flags uint32 = 0
+	if exclusive {
+		flags |= LOCKFILE_EXCLUSIVE_LOCK
+	}
+
+	// Lock the entire file (offset 0, length 0 means entire file)
+	// Retry with exponential backoff to handle contention
+	var attempts int
+	for {
+		err := windows.LockFileEx(windows.Handle(lf.Fd()), flags, 0, 1, 0, &windows.Overlapped{})
+		if err == nil {
+			return lf, nil
+		}
+
+		// Check if it's a lock violation (another process holds the lock)
+		if err == windows.ErrLockViolation || err.(windows.Errno) == ERROR_LOCK_VIOLATION {
+			attempts++
+			if attempts >= 10 {
+				_ = lf.Close()
+				return nil, fmt.Errorf("timeout waiting for lock on %q: %w", lp, err)
+			}
+			// Exponential backoff: 1ms, 2ms, 4ms, 8ms, 16ms...
+			sleepMs := 1 << (attempts - 1)
+			if sleepMs > 100 {
+				sleepMs = 100
+			}
+			windows.Sleep(uint32(sleepMs))
+			continue
+		}
+
+		// Other error - fail
+		_ = lf.Close()
+		return nil, fmt.Errorf("LockFileEx failed on %q: %w", lp, err)
+	}
 }
 
 func (sc *SourceCache) releaseLock(lf *os.File) {
+	// Unlock the entire file
+	windows.UnlockFile(windows.Handle(lf.Fd()), 0, 0, 1, 0)
 	_ = lf.Close()
 }