CS 452/652 Winter 2020 - Lecture 9

SRR for Producer/Consumer

• single producer, single consumer (SPSC)
  • producer sends, consumer responds with ack: "push" communication
  • consumer sends/requests, producer responds with element: "pull" communication
• multiple producers, single consumer (MPSC)
  • push communication works ⇒ producers are senders
  • pull communication: slow producer might block consumer (and thus other producers)
• single producer, multiple consumers (SPMC)
  • push communication: slow consumer might block produce (and thus other consumers)
  • pull communication works ⇒ consumers are senders
• multiple producers, multiple consumers (MPMC)
  • need intermediary: buffer ("distributor", "warehouse")
  • buffer: acts as single consumer to producers, single producer to consumers
  • buffer full or empty: block respective producer(s)/consumer(s)?
    • design decision: blocking vs. non-blocking (return error) operation
  • buffer receives requests, processes request, (delayed?) response
  • buffer never sends, only receives ⇒ server pattern

Name Resolution

• pervasive topic in computer science
• examples:
  • systems: memory address - name for circuit, name for device register
  • programming: variable - name for memory location or register
  • operating system: file - name for data on disk
  • Internet: DNS - name for IP address
  • Internet: URL - name for remote file/service and access protocol
• name resolution always starts in a default context with a default starting point!
  • file system: / (slash) & kernel
  • Internet domain names: . (dot) & local resolver
• this is called closure mechanism
• here: default name server
  • implicit/default starting point: tid of name server
  • use hack: global, hard-coded, other?
• tid-based communication facilitated by kernel (see 'Communication' earlier)

Name Server

• names are null-terminated character arrays
• maximum length? error? truncate?
• WhoIs()for non-existing name? error? block?
• RegisterAs() overwrites previous registration for same name
• design of name server (data structure and operation):
  • how many names?
  • how often is name server used? when?
  • latency-critical?

Memory Isolation

• visibility: routine, file, global → limited protection
• use visibility as much as possible to protect memory
• software protection
  • programming languages (compiler & runtime): Go, Java, Rust
• location: stack, data, heap
  • hardware protection via MMU (not mandatory)