Bulat Ziganshin wrote:
Hello Simon,
Monday, March 5, 2007, 3:59:17 PM, you wrote:
my Streams library [1] don't uses this thread
at all. for threads created with forkOS it provides excellent
overlapping of I/O and computations (thanks, Simon, situation was
*greatly* improved in 6.6). of course, it should be not so great for
forkIO'd threads
I don't understand why forkOS should be any different from forkIO in this
context. Could you explain?
There seems to be a common misconception that forkOS is necessary to get certain
kinds of concurrency, and forkIO won't do. I don't know where this comes from:
the documentation does seem to be quite clear to me. The only reason to use
forkOS is for interacting with foreign code that uses thread-local state;
everytyhing else can be done with forkIO (and it is usually better to use
forkIO).
it may be entirely due my ignorance :) my program anyway uses
-threaded and forkOS in order to run several C threads si,ultaneously
and i don't performed tests in any other conditions
so, one thread may read data from file, another thread write data and
one more make compression using C routine. in 6.4, these tasks was
overlapped only partially while in 6.6 they 100% overlap
don't forget that read/write calls are also foreign calls, so while
all C calls are marked as "safe", 6.4 doesn't overlap them good
enough (also, to make things harder, C compression routine makes calls
back to the Haskell routines). if haskell runtime will create new
threads for executing other Haskell threads while one thread performs
safe C call, then it should be ok. probably, i just mixed up forkOs
and -threaded mode :)
Ok, there was a complete rewrite of the scheduler between 6.4 and 6.6 so this
may account for the differences you see.
Beware of forkOS: it'll reduce performance on the Haskell side, because
essentially each context switch between a forkOS'd thread and another thread is
a complete OS-thread context switch, which is hundreds of times slower than
context switching between forkIO'd threads.
Cheers,
Simon
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