Serial-Server Strategy

1
Serial-Server Strategy
Server
Client
Client Request
Two-Way Communication

• Two way channel is for additional interaction
  between client and server
• Initial client request serves to establish two
  way communication channel
• Communication channel is private not accessable
  to other processes
• A busy server handling long-lived requests cannot
  use serial server strategy

2
Serial-Server Pseudocode
for () listen for client request
create private two-way communication channel
while (no error on communication channel)
read client request handle request and
respond to client close communication
channel
3
Parent-Server Strategy
Server
Client
Client Request
fork
Server Child
Two-Way Communication

• Server resumes listing for more requests
• Server forks a child to handle actual service
• Similar to switchboard at hotel
• Server can accept multiple client requests

4
Parent-Server Pseudocode
for () listen for client request
create a private two-way communication channel
fork a child to handle the request close the
communication channel clean up zombies
5
Thread-Server Strategy
Server Threads
Client
Client Request
Two-Way Communication

• Low overhead alternative to parent-server
  strategy
• Create thread to handle request instead of
  forking child threads have less overhead
• Efficient if request is small or I/O intensive
• Possible interference among multiple requests due
  to shared address space
• For computationally intensive services,
  additional threads may reduce efficiency of or
  block the main server thread
• Requires good kernel-level parallelism

6
Call

• rcp cougar path1 path2
• argv0 rcp
• argv1 cougar
• argv2 path1
• argv3 path2

7
Client Send Path1

• Client Bundle up path1 and send to server using
  network communications
• write(commfd, argv2, sizeof(argv2))

8
Server Receive Path1

• for ( ) if ((bytesread
  read(commfd, p_buf, BLKSIZE)) lt 0)
  read error break else if
  (bytesread 0) break
• t_fd open(p_buf, O_RDONLY)

9
Server Read Path1 into s_buf and Send Contents to
Client

• for ( ) if ((bytesread read(t_fd,
  s_buf, BLKSIZE)) lt 0) file read error
• break else if (bytesread
  0) break else if (bytesread
  ! write(commfd, s_buf,
  (size_t)bytesread)) server write
  error break

10
Client Receive

• p2fd open(argv3, O_WRONLY)
• for ( )
• if ((bytes_read read(commfd, c_buf, BLKSIZE))
  lt 0) client read error break else
  if (bytes_read 0) break else /
  allow for interruption of write by signal /
  for (bufp c_buf, bytes_to_write bytes_read
  bytes_to_write gt 0 bufp
  bytes_written, bytes_to_write - bytes_written)
  bytes_written write(p2fd, bufp,
  bytes_to_write) if ((bytes_written)
  -1 (errno ! EINTR)) client
  write error break