软件需求通常描述已经存在的或是未来的软件系统，并且应该与业务需求同步。
Software requirements are usually documented for existing or future software systems and should be in-sync with business requirements.
当资源与文件系统同步时，Eclipse将传递给插件一个delta，即上一次同步之后的变动列表。
When resources are synchronized with the file system, Eclipse passes the plug-in a delta, the list of changes since the last synchronization.
msync()：用来让共享内存段与文件系统同步 — 当把文件映射到内存时，这种技术有用。
msync(): Used to synchronize a shared memory segment with the file system—a technique useful when mapping a file into memory.
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