The document discusses the fundamentals of threads and processes, including their definitions, types, and characteristics, such as resource sharing and communication methods. It highlights the advantages and features of multithreading, user-defined and daemon threads, as well as kernel versus user-level thread management. Additionally, it covers thread lifecycle, system calls for creation and management, and differences between lightweight processes and traditional processes.

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Threads
Basic
SOUMEN SANTRA
MCA, M.Tech, SCJP, MCP
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Single vs. Multithreaded Processes
THREADS : Basic
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Thread Usage: Multitasking
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Thread : Features
Block for long waits.
Use many more CPU cycles.
Respond to asynchronous events.
Parallel performance.
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User-define Threads &
Daemon Threads
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Processes vs. Threads
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Threads vs. Processes
• Each thread executes separately
• Threads in the same process share resources
• No protection among threads!!
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Property
Processes created
with fork
Threads of a process Ordinary function calls
variables
get copies of all
variables
share global variables share global variables
IDs get new process IDs
share the same process ID
but have unique thread ID
share the same
process ID (and thread
ID)
Communicatio
n
Must explicitly
communicate,
e.g.pipes
or use small integer
return value
May communicate with return
value
or shared variables
if done carefully
May communicate with
return value
or shared variables
(don't have to be
careful)
Parallelism
(one CPU)
Concurrent Concurrent Sequential
Parallelism
(multiple
CPUs)
May be executed
simultaneously
Kernel threads may be
executed simultaneously
Sequential
Threads vs Processes
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 Resource Sharing
 Reacting fast.
 Economic Feasible.
 Utilization of Architectures or Platform.
THREADS : Benefits
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User Define Threads
 Thread management done by user-level threads library maps to kernel thread.
Examples
- Windows 95/98/NT/2000
- Linux
- POSIX Pthreads
- Mach C-threads
- Solaris threads
THREADS : Types
Daemon Threads
 Many user-level threads mapped to single kernel thread.
Examples:
 Solaris Green Threads
 GNU Portable Threads
- Windows 95/98/NT/2000
- Tru64 UNIX
- BeOS
- Linux
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Daemon Threads vs. User Threads
 Kernel/Daemon Thread
 Make blocking I/O calls without blocking the entire process.
 Perform concurrently on multiple processors
 User-level Thread
 Fast context switch
 Customized scheduling & synchronizing
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12. Kernel Threads
 kernel_thread(): to create a kernel thread.
 Example of kernel process:
 Process 0 (swapper), the ancestor of all processes.
 Process 1 (init) for initialization.
 Others: keventd, kswapd, kflushd (also bdflush), kupdated…
Here ends with ‘d’ which means daemon and ‘k’
means kernel.
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Multithreading Concept
One-to-One
Many-to-One
Many-to-Many
THREADS : Mapping
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System calls
 fork() : Used to create Child Threads.
 exec() : Used to execute Child Threads.
Thread cancellation
 Terminating a thread before job finished.
 Two general approaches:
 Asynchronous cancellation terminates the target thread
immediately. Not always follow due to creation of orphan or
zombie process.
 Deferred cancellation allows the target thread periodically
from its child.
THREADS : Issues
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 It is used in UNIX systems to notify a process has performed.
 Generated by specific event.
 Delivered to a process.
 Options:
 Delivers the signal to the thread to which the signal applies.
 Delivers the signal to every threads.
 Delivers the signal to certain threads.
 Assign a particular thread to receive all signals.
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THREADS : Signal handling

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 Generate a number of threads in a pool where they wait to yield a work.
 Advantages:
 Faster to service a request with an existing thread than create a new
thread.
 Allows the number of threads in the process within the size of the pool.
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THREADS : pools

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Pthreads
 A POSIX Application Programming Interface.
 It is used to creation and synchronization of thread.
 Standardized as IEEE 1003.1c.
 API specifies behavior of the thread library, implementation is up to
development of the library.
 Use in UNIX operating systems (Solaris, Linux, Mac OS X).
Windows Threads
 Use as one-to-one mapping.
 Each thread context contains
 A thread id (TID)
 Set of Register
 Use Separate user and kernel stacks.
 Private data store
THREADS : Implementations
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Threads in Linux
 Refers as tasks.
 call clone() system to creation of thread.
 It allows a child task to share the address space with the parent task.
Threads in Java
 Created by:
 Inherited Thread class.
 Implements the Runnable interface.
 It managed by the JVM.
THREADS : Lifecycle
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19. Processes : Lightweight
 Process: It is an instance of a program in execution.
 Lightweight process (LWP): used for multithreaded applications.
 Share resources: address space, open files, etc
 Associate with each other.
 Examples of LWP: Linux Threads, IBM’s Next Generation
Posix Threading Package (NGPT)
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20. Process : Identification
 Process descriptor pointers: 32-bit
 Process ID (PID): 16-bit
In Linux each process (LWP) has different PID.
Programmers think threads in the same group
having common PID.
Thread group: Collection of LWPs.
The PID of the first LWP is PID of the group.
TGID (Thread Group ID) is acting as process
descriptor using getpid() system call.
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21. Processes : Creation
 Resources are duplicated for parent process.
 Slow and inefficient process.
 Mechanisms to solve this problem
Copy on Write: Both read the same physical
pages.
Lightweight process: Both share per-process
kernel data structures..
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22. System Calls
 clone(func, args, flags, child_stack,parent_tid,
child_tid): creating lightweight process
A wrapper function in C library
Uses clone() system call
 fork(): discuss earlier
 vfork(): share the memory address space
 do_fork() function
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23. System calls : Organized of Processes
 TASK_RUNNING
 TASK_STOPPED,
 EXIT_ZOMBIE,
 EXIT_DEAD
 TASK_INTERRUPTABLE,
 TASK_UNINTERRUPTABLE
 Two kinds of sleeping processes
Exclusive process
Nonexclusive process
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24. THANK YOU
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