#8684: hWaitForInput cannot be interrupted by async exceptions on unix -------------------------------------+------------------------------------- Reporter: nh2 | Owner: snoyberg Type: bug | Status: patch Priority: normal | Milestone: Component: Core Libraries | Version: 7.6.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D42 Wiki Page: | -------------------------------------+------------------------------------- Description changed by nh2: Old description:
http://hackage.haskell.org/package/base-4.6.0.1/docs/System-Timeout.html
claims that {{{timeout}}} can interrupt {{{hWaitForInput}}}, but in fact that's false (e.g. mentioned in https://ghc.haskell.org/trac/ghc/ticket/7353#comment:4).
{{{ -- import Control.Concurrent import System.IO import System.Timeout
main = timeout (1 * 1000000) $ hWaitForInput stdin (5 * 1000) }}}
will not be killed after 1 second, but instead wait for the full 5 seconds timeout passed to {{{hWaitForInput}}}.
The implementation is {{{ready}}} at http://www.haskell.org/ghc/docs/latest/html/libraries/base/src/GHC-IO- FD.html, where we have two foreign calls: {{{safe fdReady}}} and {{{unsafe unsafe_fdReady}}}.
The actual C implementation is at https://github.com/haskell- suite/base/blob/master/cbits/inputReady.c#L16. It uses {{{select}}} on Unix, and does check for {{{EINTR}}}, so I believe that according to http://www.haskell.org/ghc/docs/7.6.3/html/users_guide/ffi.html#ffi- interruptible both foreign calls can be replaced by a single {{{interruptible}}} one.
Is that true?
If not, it's a documentation bug in {{{timeout}}} at least.
Also, does {{{interruptible}}}, apart from allowing the function to be interrupted, behave more like {{{safe}}} or {{{unsafe}}}?
New description: http://hackage.haskell.org/package/base-4.6.0.1/docs/System-Timeout.html claims that {{{timeout}}} can interrupt {{{hWaitForInput}}}, but in fact that's false (e.g. mentioned in https://ghc.haskell.org/trac/ghc/ticket/7353#comment:4). {{{ -- import Control.Concurrent import System.IO import System.Timeout main = timeout (1 * 1000000) $ hWaitForInput stdin (5 * 1000) }}} will not be killed after 1 second, but instead wait for the full 5 seconds timeout passed to {{{hWaitForInput}}}. The implementation is {{{ready}}} at https://downloads.haskell.org/~ghc/7.6.3/docs/html/libraries/base/src/GHC- IO-FD.html, where we have two foreign calls: {{{safe fdReady}}} and {{{unsafe unsafe_fdReady}}}. The actual C implementation is at https://github.com/ghc/packages- base/blob/52c0b09036c36f1ed928663abb2f295fd36a88bb/cbits/inputReady.c#L16. It uses {{{select}}} on Unix, and does check for {{{EINTR}}}, so I believe that according to http://www.haskell.org/ghc/docs/7.6.3/html/users_guide/ffi.html#ffi- interruptible both foreign calls can be replaced by a single {{{interruptible}}} one. Is that true? If not, it's a documentation bug in {{{timeout}}} at least. Also, does {{{interruptible}}}, apart from allowing the function to be interrupted, behave more like {{{safe}}} or {{{unsafe}}}? -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8684#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler