Re: [GHC] #11836: Hello World Bug - silent stdout errors

2 Feb 2017

      #11836: Hello World Bug - silent stdout errors
-------------------------------------+-------------------------------------
        Reporter:  bit               |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  7.10.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #11180            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by siddhanathan):

 The first case is interesting.

 The following should fail as intended:

 {{{#!hs
 import System.IO

 main = do
   hSetBuffering stdout (BlockBuffering (Just 14))
   putStrLn "Hello, World!"
 }}}

 {{{
 $ ghc hello.hs
 [1 of 1] Compiling Main             ( hello.hs, hello.o )
 Linking hello ...

 $ ./hello > /dev/full ; echo $?
 hello: <stdout>: commitBuffer: resource exhausted (No space left on
 device)
 1
 }}}

 But one small change can make it silently succeed:

 {{{#!hs
 import System.IO

 main = do
   hSetBuffering stdout (BlockBuffering (Just 15))
   putStrLn "Hello, World!"
 }}}

 {{{
 $ ghc hello.hs
 [1 of 1] Compiling Main             ( hello.hs, hello.o )
 Linking hello ...

 $ ./hello > /dev/full ; echo $?
 0
 }}}

 In the absence of an explicit statement for setting the buffering mode,
 the code might be similar to this:

 {{{#!hs
 import System.IO

 main = do
   hSetBuffering stdout (BlockBuffering Nothing)
   putStrLn "Hello, World!"
 }}}

 in which case, GHC may resort to using a fairly large number like
 `dEFAULT_CHAR_BUFFER_SIZE`. To verify that this is the case, you could try
 the following:

 {{{#!hs
 main = putStrLn $ replicate (1024*8) '.'
 }}}

 and now things are consistent again:

 {{{
 $ ghc hello.hs
 [1 of 1] Compiling Main             ( hello.hs, hello.o )
 Linking hello ...

 $ ./hello > /dev/full ; echo $?
 hello: <stdout>: commitBuffer: resource exhausted (No space left on
 device)
 1
 }}}

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11836#comment:6
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