mutex example

[friend.blah@googlemail.com]

can any one give a simple example for implementing mutex.
I have 3 threads (taking different input files )enter into the same
function at different times...

The 3 threads need to exit/leave the function till all the input files
reached till end which are taken as input to the threds.


thanks to all

[Victor Bazarov]

Re: mutex example

friend.blah@goo glemail.com wrote:

can any one give a simple example for implementing mutex.
I have 3 threads (taking different input files )enter into the same
function at different times...
>
The 3 threads need to exit/leave the function till all the input files
reached till end which are taken as input to the threds.

At this point "mutex" or any other synchronisation object are platform-
specific. Consider asking your question in the newsgroup for your platform.

V
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[Pascal J. Bourguignon]

Re: mutex example

"friend.blah@go oglemail.com" <friend.blah@go oglemail.comwri tes:

can any one give a simple example for implementing mutex.
I have 3 threads (taking different input files )enter into the same
function at different times...
>
The 3 threads need to exit/leave the function till all the input files
reached till end which are taken as input to the threds.

So you want the three threads in the same function at the same time.
So you want absolutely no mutual exclusion, but exactly the opposite,
you want mutual INCLUSION!

You should try to express what you want more clearly. For example,
you could start with something more grammatically correct. I have
really a hard time parsing this sentence:

"The 3 threads need to exit/leave the function till all the input
files reached till end which are taken as input to the threds."


Let's assume what you want is:


thread 1
|
|
v
----- enter function
|
|
v
(go on reading file 1)
| thread 2
| |
| |
| v
| ----- enter function
| |
| |
| v
| (go on reading file 2)
| |
| |
| |
| | thread 3
| | |
| | |
| | v
| | ----- enter function
| | |
| | |
| | v
| | (go on reading file 3)
v | |
----- reach eof v |
| ----- reach eof |
| | v
| | ----- reach eof
| | |
v v v
---------------------------------------------------- exit function
| | |
| | |
v v v


The synchronization at the exit function could be implemented with a
condition.


initialize:
- a counter = 0
- a mutex m
- a condition c



synchronized_ex it(n)
mutext_lock(m)
increment counter
if (counter >= n) then
condition_broad cast(c)
counter=0
else
condition_wait( c,m)
endif
mutext_unlock(m )


All three threads shall call synchronized_ex it(3) after reaching their EOF.


man pthread_cond_in it pthread_cond_wa it pthread_cond_br oadcast
man pthread_mutex_i nit pthread_mutex_l ock pthread_mutex_u nlock


--
__Pascal Bourguignon__