Threads and Processes

JMU

Threads and Processes
A Comparison

Prof. David Bernstein
James Madison University

Computer Science Department

bernstdh@jmu.edu

Review

Multi-Processing:
- Concurrent programs can involve multiple processes
Multi-Threading:
- Concurrent programs can involve multiple threads

Advantages of Threads

Data Sharing:
- Threads can share data using variables with file scope (processes need to use an IPC mechanism like a file, pipe/FIFO, shared memory segment, message queue, etc..)
Speed:
- Threads can be created more quickly than processes
- Context switches may be faster for threads than processes

Advantages of Processes

Safety:
- Functions called by multiple threads must be "thread safe"
- A defect in one thread can damage all of the threads in a process (since they share the same address space and other attributes)
Resources:
- Threads share the resources (e.g., address space) of a single process
Signals:
- Are very hard to use in multi-threaded programs

Advantage or Disadvantage?

Text/Code Segment:
- All threads must run the same program
- Different processes can run different programs
Shared Information:
- Threads share file descriptors, the working directory, and various IDs
- Processes "inherit" file descriptors, can have a different working directory, and have different IDs