Blocking I/O: What is That? (“Everything is a file”)

Examples/Live Demos

• Blocking I/O (On A File): What is That?

• Blocking I/O: On A Network Socket

• Blocking I/O: On A Timer? WTF?

Problem

Communication with hardware is rarely synchronous

• Initiate an action: “Hey, disk: move heads to position such-and-such”

• Do something else (?) until action is complete ⟶ interrupt

• React; for example: setup DMA to receive data from disk heads

• Do something else (?) until DMA is complete ⟶ interrupt

Danger

Nobody wants to do this in day-to-day code!

Solution: This Is What An Operating System Is There For

Say what you want:

• Open a file, for example, such as /etc/passwd. Do not bother me with asynchronicity, like …

  • I don’t have anything else to do in the meantime, so I don’t want to be notified. Me stupid!

  • I just want to sit there until everything is complete (don’t want to think about what “Everything” is)

  • When all is fine, I want a handle to that open file

  • When nothing’s fine, I want an error

• Read me n bytes into a buffer I supply. Again, no asynchronicity, please!

• ⟶ Simplicity rules!

• ⟶ The “File” Abstraction!

• Question: who’s me? ⟶ a process