7/9/08

Multi-threading basics

By multi threading many things can be done at once. One can divide a single task into multiple parts and execute simultaneously. More than one thread running simultaneously. On single processor systems its usually utilities the IO operation time with other concorruntly running thread to utilize CPU at its fullest strength. but on multiple processor systems, its truly executes the threads concoruntly.

Windows Operating system time slices the cpu time and allocates to each thread.
on expiring the time slice, thread is paused.

Context Switching
the state( CPU Registers and other data) of the thread is saved.
Another threading waiting for its slice will started. paused as above.
when it comes to the first threads time its is reloaded and resumed.

Can have base and dynamic priorities. base can be changed but not more than parent.
dynamic is same as base except can be raised or lowered by windows.
OS(win) chooses which thread to run next based on dynamic priority.

Every program has a primary thread can be used to create other thread.
These objects are created by windows object manager.

WaitForSingleObject() waits for a thread(object) to return.
if provided time out waits till lapse of time period.
if it is INFINITE wait till thread returns.

WaitforMultipleObject() waits for no. of object
can wait for all object or can wait to return single object rest same as WaitForSingleObejct.


Mutex
can be owned by a single thread at a time. all other will wait till that thread owns.
once released others can own and access the resources owned by first thread.


Semaphores:

Allows only a limited no. of threads to access protected resources.
Multiple threads can own it at a time.
Can have initial count and max count.
Initially initial count is equal to max. as owns by a thread it is decremented,
once it is zero, no more threads are allowed to access resources.

Critical Sections:
same as Mutex, can be owned by one thread at a time. can work withing process.
while mutex can work across process.


Events:
if one wants to alert, threads of some action is occuring.
SetEvent is called to signal a state to all the threads waiting for it.
PulseEvent used to quickly set-reset signals.
These can be autoreset or manual reset events.
if manualreset =fasle( auto) will created and call setevent and changed to non signaled state.
if initialstate =true created and sets to signaled state

1 comment:

Anonymous said...

Horrible grammar throughout the article