1.7 Supporting Interactions Across Time

Storage

OS provides long-term storage for computation results
Results can be retrieved for future computations

File system

Named persistent storage
Typically organized in a hierarchy

File access

Accessed via OS APIs (read, write)
May be mapped to memory space and accessed directly with load and store

Databases

Provide persistent storage
Allows related data to be access easily

What if the system goes down during a write?

Crashes

Any operation should be immediately interruptable without leaving persistent storage in a degraded state
Atomic transactions and journaling may be a solution to this

1.8 Supporting Interactions Across Space

Networking

Provides a means for separate systems to interact
Network stack organized into layers

Sockets

Provides a standard and consistent API for applications to use for networking
Supports streaming and packet-based communication

Socket types

Stream - provides a virtual circuit
Datagram - delivers individual packets

Socket Implementation

Independent of network type
Most typically used with TCP/IP and UDP/IP

Socket States

if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
  return 1;
}

if( connect(sockfd, &serv_addr, sizeof(serv_addr)) < 0) {
  return 1;
}

if (n = read(sockfd, recvBuff, sizeof(recvBuff)-1)) <= 0) {
  return 1;
}

printf("%s\n", recvBuff);