用ajax单独上传文件，用php处理可能的竞争条件？

function uploadFile(file) {
    var formData = new FormData();
    formData.append('file', file);

    $.ajax({
        url: 'upload.php',
        type: 'POST',
        data: formData,
        processData: false,
        contentType: false,
        success: function(response) {
            console.log('File uploaded successfully:', response);
        },
        error: function(xhr, status, error) {
            console.error('File upload failed:', error);
        }
    });
}

<?php
$targetDir = 'uploads/';
$response = [];

if (isset($_FILES['file'])) {
    $file = $_FILES['file'];
    $fileName = uniqid() . '_' . basename($file['name']);
    $targetFile = $targetDir . $fileName;

    if (move_uploaded_file($file['tmp_name'], $targetFile)) {
        $response['message'] = 'File uploaded successfully';
        $response['fileName'] = $fileName;
    } else {
        $response['error'] = 'Failed to move uploaded file';
    }
} else {
    $response['error'] = 'No file uploaded';
}

echo json_encode($response);
?>