.The `glibc` `getenv` function provides a limited form of thread safety   The `glibc` `getenv` function is not thread safe. Previously, if an application still called the functions `getenv`, `setenv`, `unsetenv`, `putenv`, and `clearenv` at the same time, the application they could terminate unexpectedly or `getenv` could return incorrect values. With this bug fix, the `getenv` function provides a limited form of thread safety. As a result, applications no longer crash if they call the functions concurrently. Additionally, `getenv` returns only environment values that have been using `setenv` or which were present at the start of the program, and reports previously-set environment variables as unset only if there has been a potentially unordered `unsetenv` call. This fix is not applicable if you directly modify the `environ` array.