[DllImport("libclient.so", EntryPoint = "readFifo")]

    private static extern int readFifo(int clientFd);

If you have control over the library name, keep the above naming conventions in mind and don’t use a platform-specific library name in the DllImport statement. Instead, just use the library name itself, without any prefixes or suffixes, and rely on the runtime to find the appropriate library at runtime. For example:

 [DllImport ("MyLibrary")]

 private static extern void Frobnicate ();

Then, you just need to provide MyLibrary.dll for Windows platforms, libMyLibrary.so for Unix platforms, and libMyLibrary.dylib for Mac OS X platforms.

[DllImport("client", EntryPoint = "readFifo")]

    private static extern int readFifo(int clientFd);