cse threads review

Multithreads Benefits:

Many-to-One:
- Solaris Green Threads
- GUN Portable Threads
One-to-One:
- Windows NT/XP/2000
- Linux
- Solaris 0 and later
Many-to-Many:
- Windows NT/2000 with the ThreadFiber package
- Solaris prior to version 9
Two-level Model:
- IRIX
- HP-UX

Pthreads
- May be provided either as user-level or kernel-level
- A POSIX standard API for thread creation and synchronization
- API specifies behavior of the thread library, implementation is up to development of the library
- Common in UNIX operating systems
Java Threads
- Java threads are managed by the JVM
- Typically implemented using the threads model provided by underlying OS
- Java threads may be created by
  - Extending Thread class
  - Implementing the Runnable interface

Semantics of fork() and exec() system calls
Thread cancellation of target thread (Asynchronous or deferred)
Signal handling (Synchronous and asynchronous)
- process signals:
  - Signal is generated by particular event
  - Signal is delivered to a process
  - Signal is handled
- Options:
  - Deliver the signal to the thread to which the signal applies
  - Deliver the signal to every thread in the process
  - Deliver the signal to certain threads in the process
  - Assign a specific thread to receive all signals for the process
Thread pools
- Advantages:
  - Usually slightly after to service a request with an existing thread than create a new thread
  - Allows the number of threads in the application be bound to the size of the pool
Thread-specific data
- Allows each thread to have its own copy of data
- Useful when do not have control over the thread creation process(i.e when using a thread pool)
Scheduler activations
- Both M:M and Two-level models require communication to maintain the appropriate number of kernel threads allocated to the application
- Scheduler activations provide upcalls - a communication mechanism from the kernel to the thread library
- This communication allows an application to maintain the correct number kernel threads

one-to-one mapping, kernel-level
Each thread contains
- A thread id
- Register set
- Separate user and kernel stacks
- Private data storage area
context of the threads
- register set
- stacks
- private storage area
primary data structures of a thread include
- ETHREAD (executive thread block)
- KTHREAD (kernel thread block)
- TEB (thread environment block)

Linux refers to them as tasks rather than threads
Thread creation is done through clone() system call
clone() allows a child task to share the address space of the parent task (process)
struct task_struct points to process data structures (shared or unique)