January 23, 2006

---

Fork and Wait Exercises

---

• exercise 3.10 from [USP], p. 69
• exercise 3.18 from [USP], p. 74
• exercise 3.20 from [USP], p. 75
• exercise 3.21 from [USP], p. 76

---

Investigating Questions from Last Class

---

• why go through the overhead of copying process image if you are simply going to replace it with another image?
  • newer versions of fork (see 3.0BSD) do not copy the process image on a fork until a modification to address space is made
    • this is called a copy-on-write
  • does system address this?
    • investigate vfork
      • same as fork but suspends the parent until an exec or exit is called
      • does not copy the process image, instead it shares it
    • system calls vfork and exec then waitpid, blocks until child terminates
• can the l family of exec calls be used when the number of arguments are unknown until run-time?
  • build a string representing the call to execlp and then invoke it
    • trivial in an interpreted, functional language such as Scheme
    • how about in C?