diff options
| -rw-r--r-- | ghc/docs/libraries/Concurrent.sgml | 15 |
1 files changed, 12 insertions, 3 deletions
diff --git a/ghc/docs/libraries/Concurrent.sgml b/ghc/docs/libraries/Concurrent.sgml index 118178c631..087baf68d6 100644 --- a/ghc/docs/libraries/Concurrent.sgml +++ b/ghc/docs/libraries/Concurrent.sgml @@ -3,7 +3,8 @@ <p> This library provides the Concurrent Haskell extensions as described -in <url name="Concurrent Haskell" url="http://research.microsoft.com/Users/simonpj/Papers/concurrent-haskell.ps.gz">. +in <url name="Concurrent Haskell" + url="http://research.microsoft.com/Users/simonpj/Papers/concurrent-haskell.ps.gz">. <tscreen><verb> module Concurrent where @@ -15,6 +16,7 @@ instance Ord ThreadId forkIO :: IO () -> IO ThreadId myThreadId :: IO ThreadId killThread :: ThreadId -> IO () +yield :: IO () data MVar a -- Synchronisation variables newEmptyMVar :: IO (MVar a) @@ -71,8 +73,7 @@ Notes: Hugs uses cooperative multitasking: Context switches only occur when you use one of the primitives defined in this module. This means that programs such as: -s not been implemented yet on -Hugs + <tscreen><verb> main = forkIO (write 'a') >> write 'b' where write c = putChar c >> write c @@ -85,6 +86,12 @@ main = forkIO (write 'a') >> write 'b' simple graphical user interfaces. <item> +The <tt>yield</tt> action forces a context-switch to any other +currently runnable threads (if any), and is occasionally useful when +implementing concurrency abstractions (especially so if the +implementation of Concurrent Haskell uses cooperative multitasking). + +<item> Hugs does not provide the functions <tt/mergeIO/ or <tt/nmergeIO/ since these require preemptive multitasking. @@ -118,4 +125,6 @@ status of the variable. The same proviso applies to <tt/isEmptyChan/. +These two predicates are currently only supported by GHC. + </itemize> |