race conditions@web

現在的系統上線前，多半會用資安軟體掃描過，以確定程式碼都符合安全規範，底下是個容易忽略的例子:

public void setUploadFolder(String upload_folder) {
    if(!StringUtils.isEmpty(upload_folder)) {
        destinationFolder = new File(upload_folder);
        destinationFolder.createNewFile();
    }
}

這是當使用者上傳檔案後，開啟一個檔案然後準備存檔，為什麼這段程式有問題? 因為，web 程式是多人使用的系統，每個人登入會產生自己的 thread，如果兩個人同時執行到上述的程式，就會產生 race condition，解決的辦法就是加上同步機制，以確保這段程式碼 thread-safe。






【每日一字】
to have no choice but to: to be forced to do something; to have no other option but ...; to have no choice to do anything except ... (除了…外別無選擇,只好,不得不)
* We were lost in the forest, very hungry and tired, but we had no choice but to continue walking to try to get home.
(資料來源: ESL Podcast 287)