Threads Two - Operating Systems - Lecture Slides, Slides of Computer Science

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Operating Systems

Lecture 08:

Threads

Processes vs. Threads

• A process viewed so far as units of:
  • Resource ownership
  • Scheduling/execution
• In multithreading OS:
  • Process stays the unit of resource ownership
  • Thread (or lightweight process ) is the unit of scheduling
• Multithreading: the ability of an OS to

support multiple, concurrent paths of

execution within a single process Docsity.com^2

One or More Threads

in a Process

Each thread in a process has:

• A thread execution state (Running, Ready, etc.)
• A saved thread context when not running; one way to view a thread is as an independent program counter operating within a process
• An execution stack
• Some per-thread static storage for local variables
• Access to the memory and resources of its process, shared with all other threads in that process

Threads vs. Processes

Thread Use in a

Single-User System

• Foreground and background work

• Asynchronous processing

• Speed of execution

• Modular program structure

Threads

• In an OS that supports threads, scheduling

and dispatching is done on a thread basis

• Most of the state information dealing with

execution is maintained in thread-level data

structures

• suspending a process involves suspending all threads of the process
• termination of a process terminates all threads within the process

2 RPCs with

single thread

and multi- threading

Multithreading on a Uniprocessor

User-Level Threads (ULTs)

• All thread management is done by the application
• The kernel is not aware of the existence of threads

Relationships Between ULT

States and Process States

Figure 4.6 Examples of the Relationships between User-Level Thread States and Process States

Disadvantages of ULTs

• In a typical OS many system calls are blocking

 as a result, when a ULT executes a system call, not only is that thread blocked, but all of the threads within the process are blocked

• In a pure ULT strategy, a multithreaded

application cannot take advantage of multiprocessing

Kernel-Level Threads (KLTs)

• Thread management is done by the kernel - no thread management is done by the application - Windows is an example of this approach

Disadvantage of KLTs

The transfer of control from one thread to

another within the same process

requires a mode switch to the kernel

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Combined Approaches

• Thread creation is done in the user space
• Bulk of scheduling and synchronization of threads is by the application
• Solaris is an example