Unix是否对单个文件进行原子序列化读写?

I'd like to know if the writes upon a single file get done atomically such that write("bla bla") and a subsequent write("herp derp") to the same file never results in interleaving, e.g. "bla herp bla derp". Assuming these writes happen in different processes or threads, what governs which gets done first?I'd like to know if the writes upon a single fi