1. Concurrency and Threading: Introduction
CSCE 410/611 : Operating Systems
Concurrency and Threading: Introduction
Concurrency: “Why?”
Concurrency: ”How?”
Serial, Collaborative, and Preemptive Task Management
Concurrent Tasks and Shared Global State
Preemptive Task Management: Threads
Example: POSIX pthreads
Concurrency and Threading: Introduction

2. CSCE 410/611 : Operating Systems
Concurrency: “Why?”
1. Latency Reduction:
Apply parallel algorithm.
Concurrency in trivially parallelizable problems.
client
server
task
task
task
Concurrency and Threading: Introduction

3. CSCE 410/611 : Operating Systems
Concurrency: “Why?”
1. Latency Reduction:
Apply parallel algorithm.
Concurrency in trivially parallelizable problems.
2. Latency Hiding:
Use concurrency to perform useful work while another operation is pending. (multiprogramming)
Latency of operation is not affected, but hidden.
client
client
client
server
server
server
task
task
task
Concurrency and Threading: Introduction

4. CSCE 410/611 : Operating Systems
Concurrency: “Why?”
1. Latency Reduction:
Apply parallel algorithm.
Concurrency in trivially parallelizable problems.
2. Latency Hiding:
Use concurrency to perform useful work while another operation is pending. (multiprogramming)
Latency of operation is not affected, but hidden.
3. Throughput Increase:
Employ multiple concurrent executions of sequential threads to accommodate more simultaneous work.
Concurrency is then handled by specialized subsystems (OS, database, etc.)
client
client
server
task
task
Concurrency and Threading: Introduction

5. CSCE 410/611 : Operating Systems
Concurrency: “How?”
Definition [Task]: Control flow.
client
client
Serial Task Management:
Execute each task to completion before starting new task.
server
task
Concurrency and Threading: Introduction

6. CSCE 410/611 : Operating Systems
Concurrency: “How?”
Definition [Task]: Control flow.
client
client
Serial Task Management:
Execute each task to completion before starting new task.
server
task
Concurrency and Threading: Introduction

7. CSCE 410/611 : Operating Systems
Concurrency: “How?”
Definition [Task]: Control flow.
client
client
Serial Task Management:
Execute each task to completion before starting new task.
Cooperative Task Management:
(Voluntarily) yield CPU at well-defined points in execution.
server
task
task
task
Concurrency and Threading: Introduction

8. CSCE 410/611 : Operating Systems
Concurrency: “How?”
Definition [Task]: Control flow.
client
client
Serial Task Management:
Execute each task to completion before starting new task.
Cooperative Task Management:
(Voluntarily) yield CPU at well-defined points in execution.
server
task
task
task
you go!
Concurrency and Threading: Introduction

9. CSCE 410/611 : Operating Systems
Concurrency: “How?”
Definition [Task]: Control flow.
client
client
Serial Task Management:
Execute each task to completion before starting new task.
Cooperative Task Management:
(Voluntarily) yield CPU at well-defined points in execution.
server
task
task
task
thanks!
Concurrency and Threading: Introduction

10. CSCE 410/611 : Operating Systems
Concurrency: “How?”
Definition [Task]: Control flow.
client
client
Serial Task Management:
Execute each task to completion before starting new task.
Cooperative Task Management:
(Voluntarily) yield CPU at well-defined points in execution.
Preemptive Task Management:
Execution of tasks can interleave.
server
scheduler
task
task
Concurrency and Threading: Introduction

11. CSCE 410/611 : Operating Systems
Concurrency: “How?”
Definition [Task]: Control flow. Tasks have access to shared global state.
client
client
Serial Task Management:
Execute each task to completion before starting new task.
Cooperative Task Management:
(Voluntarily) yield CPU at well-defined points in execution.
Preemptive Task Management:
Execution of tasks can interleave.
server
scheduler
task
task
task
task
shared global state
Concurrency and Threading: Introduction

12. CSCE 410/611 : Operating Systems
Shared Global State
Example – Invariant: credits - debits == balance
credits = 120
debits = 120
balance = 0
credits
debits
balance
invariant holds
Definition [Invariant]: Predicate that “has to be true at all times”.
Concurrency and Threading: Introduction

13. CSCE 410/611 : Operating Systems
Shared Global State
Example – Invariant: credits - debits == balance
credits = 120
debits = 80
balance = 0
credits
debits
balance
credits = 120
debits = 120
balance = 0
invariant violated!
Definition [Invariant]: Predicate that “has to be true at all times”.
Concurrency and Threading: Introduction

14. CSCE 410/611 : Operating Systems
Concurrency: “How?”
Definition [Task]: Control flow. Tasks have access to shared global state.
client
client
Serial Task Management:
Execute each task to completion before starting new task.
Cooperative Task Management:
(Voluntarily) yield CPU at well-defined points in execution.
Preemptive Task Management:
Execution of tasks can interleave.
server
task
task
shared global state
Concurrency and Threading: Introduction

15. Serial Task Management
CSCE 410/611 : Operating Systems
Serial Task Management
Pros:
Only one task is running at a given time.
No potential for conflict in accessing shared state.
We can define so-called “inter-task invariants”; while one task is running, no other task can violate these invariants.
client
client
server
Cons:
Only one task is running at a given time!
No multiprogramming.
No multiprocessor parallelism.
task
task
Concurrency and Threading: Introduction

16. Cooperative Task Management
CSCE 410/611 : Operating Systems
Cooperative Task Management
Pros:
Allows for some controlled multiprogramming.
client
client
server
task
task
task
task
Concurrency and Threading: Introduction

17. Cooperative Task Management
CSCE 410/611 : Operating Systems
Cooperative Task Management
Pros:
Allows for some controlled multiprogramming.
client
client
server
task
task
task
task
Concurrency and Threading: Introduction

18. Cooperative Task Management
CSCE 410/611 : Operating Systems
Cooperative Task Management
Pros:
Allows for some controlled multiprogramming.
Invariants must be ensured at yielding points only.
client
client
server
you go!
task
task
task
task
Concurrency and Threading: Introduction

19. Cooperative Task Management
CSCE 410/611 : Operating Systems
Cooperative Task Management
Pros:
Allows for some controlled multiprogramming.
Invariants must be ensured at yielding points only.
client
client
server
thanks!
Cons:
Invariants are not automatically enforced.
task
task
Concurrency and Threading: Introduction

20. Preemptive Task Management
CSCE 410/611 : Operating Systems
Preemptive Task Management
Pros:
Allows for high level of multiprogramming.
Parallelism
client
client
scheduler
server
task
task
Concurrency and Threading: Introduction

21. Preemptive Task Management
CSCE 410/611 : Operating Systems
Preemptive Task Management
Pros:
Allows for high level of multiprogramming.
Parallelism
client
client
scheduler
server
task
task
Concurrency and Threading: Introduction

22. Preemptive Task Management
CSCE 410/611 : Operating Systems
Preemptive Task Management
Pros:
Allows for high level of multiprogramming.
Parallelism
client
client
scheduler
server
next!
huh?!
task
task
Concurrency and Threading: Introduction

23. Preemptive Task Management
CSCE 410/611 : Operating Systems
Preemptive Task Management
Pros:
Allows for high level of multiprogramming.
Parallelism
client
client
scheduler
server
huh?!
task
task
Concurrency and Threading: Introduction

24. Preemptive Task Management
CSCE 410/611 : Operating Systems
Preemptive Task Management
Pros:
Allows for high level of multiprogramming.
Parallelism
client
client
scheduler
server
Cons:
Invariants are must hold at all times (!?)
Mechanism: synchronization
task
task ?!
Concurrency and Threading: Introduction

25. Preemptive Task Management: “How?”
CSCE 410/611 : Operating Systems
Preemptive Task Management: “How?”
Scheduler manages threads
Process
executable
data segment
file descr.
registers
stack
scheduler
thread of control
Concurrency and Threading: Introduction

26. Preemptive Task Management: “How?”
CSCE 410/611 : Operating Systems
Preemptive Task Management: “How?”
Scheduler manages threads
Process
executable
data segment
file descr.
Thread 1
registers
registers
stack
Thread 2
registers
stack
stack
scheduler
Concurrency and Threading: Introduction

27. Example: POSIX pthreads
CSCE 410/611 : Operating Systems
Example: POSIX pthreads
pthread_create (create a thread)
pthread_cancel (terminate another thread)
pthread_detach (have thread release res’s)
pthread_equal (two thread id’s equal?)
pthread_exit (exit a thread)
pthread_kill (send a signal to a thread)
pthread_join (wait for a thread)
pthread_self (what is my id?)
Concurrency and Threading: Introduction

28. Example: POSIX pthreads
CSCE 410/611 : Operating Systems
Example: POSIX pthreads
pthread_create (create a thread)
pthread_cancel (terminate another thread)
pthread_detach (have thread release res’s)
pthread_equal (two thread id’s equal?)
pthread_exit (exit a thread)
pthread_kill (send a signal to a thread)
pthread_join (wait for a thread)
pthread_self (what is my id?)
int pthread_create(pthread_t * thread,
const pthread_attr_t * attr,
void *(*start_routine)(void *),
void * arg)
fd = open(“my.dat”, O_RDONLY);
if (error = pthread_create(&t_id, NULL, processfd, &fd))
fprintf(stderr, “Failed create thread: %s\n”, strerror(error));
Concurrency and Threading: Introduction

29. pthreads: Thread Attributes
CSCE 410/611 : Operating Systems
pthreads: Thread Attributes
attribute objects
pthread_attr_destroy
pthread_attr_init
state
pthread_attr_getdetachstate
pthread_attr_setdetachstate
stack
pthread_attr_getguardsize
pthread_attr_setguardsize
pthread_attr_getstack
pthread_attr_setstack
scheduling
pthread_attr_getinheritedsched
pthread_attr_setinheritedsched
pthread_attr_getschedparam
pthread_attr_setschedparam
pthread_attr_getschedpolicy
pthread_attr_setschedpolicy
pthread_attr_getscope
pthread_attr_setscope
Concurrency and Threading: Introduction

30. pthreads: Thread Attributes – State
CSCE 410/611 : Operating Systems
pthreads: Thread Attributes – State
attribute objects
pthread_attr_destroy
pthread_attr_init
state
pthread_attr_getdetachstate
pthread_attr_setdetachstate
stack
pthread_attr_getguardsize
pthread_attr_setguardsize
pthread_attr_getstack
pthread_attr_setstack
scheduling
pthread_attr_getinheritedsched
pthread_attr_setinheritedsched
pthread_attr_getschedparam
pthread_attr_setschedparam
pthread_attr_getschedpolicy
pthread_attr_setschedpolicy
pthread_attr_getscope
pthread_attr_setscope
Detached threads release resources when terminate.
Attached states hold on to resources until parent thread calls pthread_join.
Concurrency and Threading: Introduction

31. pthreads: Thread Attributes – Stack
CSCE 410/611 : Operating Systems
pthreads: Thread Attributes – Stack
attribute objects
pthread_attr_destroy
pthread_attr_init
state
pthread_attr_getdetachstate
pthread_attr_setdetachstate
stack
pthread_attr_getguardsize
pthread_attr_setguardsize
pthread_attr_getstack
pthread_attr_setstack
scheduling
pthread_attr_getinheritedsched
pthread_attr_setinheritedsched
pthread_attr_getschedparam
pthread_attr_setschedparam
pthread_attr_getschedpolicy
pthread_attr_setschedpolicy
pthread_attr_getscope
pthread_attr_setscope
setstack defines location and size of stack.
setguardsize allocates additional memory. If the thread overflows into this extra memory, an error is generated.
Concurrency and Threading: Introduction

32. pthreads: Thread Attributes – Scheduling
CSCE 410/611 : Operating Systems
pthreads: Thread Attributes – Scheduling
attribute objects
pthread_attr_destroy
pthread_attr_init
state
pthread_attr_getdetachstate
pthread_attr_setdetachstate
stack
pthread_attr_getguardsize
pthread_attr_setguardsize
pthread_attr_getstack
pthread_attr_setstack
scheduling
pthread_attr_getinheritedsched
pthread_attr_setinheritedsched
pthread_attr_getschedparam
pthread_attr_setschedparam
pthread_attr_getschedpolicy
pthread_attr_setschedpolicy
pthread_attr_getscope
pthread_attr_setscope
PTHREAD_INHERIT_SCHED defines that scheduling parameters are inherited from parent thread. (as opposed to PTHREAD_EXPLICIT_SCHED).
Scheduling policies: SCHED_FIFO, SCHED_RR, SCHED_SPORADIC, SCHED_OTHER, …
contention scope defines whether process competes at process level or at system level for resources.
Concurrency and Threading: Introduction

33. Concurrency and Threading: Introduction
CSCE 410/611 : Operating Systems
Concurrency and Threading: Introduction
Concurrency: “Why?”
Concurrency: ”How?”
Serial Task Management
Collaborative Task Management
Preemptive Task Management
Concurrent Tasks and Shared Global State
Preemptive Task Management: Threads
Example: POSIX pthreads
Concurrency and Threading: Introduction