uucidl

On the emergence of interfaces

Interfaces naturally emerge as software gets broken down into parts communicating with one another. The larger and more deliberate structures emerge from a deliberate attempt to organize the development process itself. [fn:Liskov2008] Structure often emerge directly from division of labor: as teams take on independent tasks, interfaces are established betweeen domains they become responsible for. (Conway’s Law)

Software developers are responsible for systems built out of very small atoms while ultimately performing tasks for their users of a much greater magnitude. Dijkstra showed this by computing the ratio between grains of time at the lowest and largest atoms of the system (from say, CPU instructions to a human interaction with the system) The span was already quite large by Dijkstra’s time, of about 10^9. Today this ratio would be at least above 10^12 (see grain ratios)

This large span has to be manage

jboner

Latency Comparison Numbers (~2012)
----------------------------------
L1 cache reference                           0.5 ns
Branch mispredict                            5   ns
L2 cache reference                           7   ns                      14x L1 cache
Mutex lock/unlock                           25   ns
Main memory reference                      100   ns                      20x L2 cache, 200x L1 cache
Compress 1K bytes with Zippy             3,000   ns        3 us
Send 1K bytes over 1 Gbps network       10,000   ns       10 us
Read 4K randomly from SSD*             150,000   ns      150 us          ~1GB/sec SSD