[Pkg-haskell-maintainers] Bug#678056: SIGALRM problem prevents using FFI to interface with FreeBSD kqueue()

[Joey Hess]

Package: ghc
Version: 7.4.1-4
Severity: normal

The attached tarball can be extracted on Debian kFreeBSD (or possibly
a real BSD system) and this bug demonstrated as follows:

(sid-kfreebsd-i386-dchroot)joeyh at fischer:~/git-annex/testcase$ make Utility/libkqueue.o
(sid-kfreebsd-i386-dchroot)joeyh at fischer:~/git-annex/testcase$ ghc --make foo Utility/libkqueue.o
(sid-kfreebsd-i386-dchroot)joeyh at fischer:~/git-annex/testcase$ gcc Utility/libkqueue.c -DSTANDALONE
(sid-kfreebsd-i386-dchroot)joeyh at fischer:~/git-annex/testcase$ ./foo &
[4] 23101
"detected a change in Nothing"
(sid-kfreebsd-i386-dchroot)joeyh at fischer:~/git-annex/testcase$ ./a.out  &
[5] 23103
(sid-kfreebsd-i386-dchroot)joeyh at fischer:~/git-annex/testcase$ touch test
change: 3

Utility/libkqueue.c is a small C library using the kqueue() interface
to tell when a directory's contents have changed. It can be built standalone
to the a.out shown above, which then behaves as shown, waiting for a change
to the current directory and printing something.

foo.hs uses this library, and should be making the same calls
to functions in it, using the FFI. However, as shown above, it fails
to wait for any changes, returning an error condition immediately.

Here's the relevant ktrace for a.out:

 24323 a.out    CALL  open(0x8048807,0<><invalid>0,<unused>0)
 24323 a.out    NAMI  "."
 24323 a.out    RET   open 3
 24323 a.out    CALL  kqueue
 24323 a.out    RET   kqueue 4
 24323 a.out    CALL  kevent(0x4,0xbfbfe638,0x1,0xbfbfe678,0x1,0xbfbfe6c4)
 24323 a.out    GIO   fd 4 wrote 20 bytes
       0x0000 0300 0000 fcff 2500 0200 0000 0000 0000  |......%.........|
       0x0010 0000 0000                                |....|

 24323 a.out    GIO   fd 4 read 0 bytes
       ""
 24323 a.out    RET   kevent 0
 24323 a.out    CALL  kevent(0x4,0xbfbfe658,0,0xbfbfe688,0x1,0)
 24323 a.out    GIO   fd 4 wrote 0 bytes
       ""
 24323 a.out    GIO   fd 4 read 20 bytes
       0x0000 0300 0000 fcff 2000 0200 0000 0000 0000  |...... .........|
       0x0010 0000 0000                                |....|

 24323 a.out    RET   kevent 1

And for foo:

 25140 foo      CALL  open(0x286fc040,0<><invalid>0,<unused>0)
 25140 foo      NAMI  "."
 25140 foo      RET   open 3
 25140 foo      CALL  kqueue
 25140 foo      RET   kqueue 4
 25140 foo      CALL  kevent(0x4,0xbfbfc598,0x1,0xbfbfc5d8,0x1,0xbfbfc624)
 25140 foo      GIO   fd 4 wrote 20 bytes
       0x0000 0300 0000 fcff 2500 0200 0000 0000 0000  |......%.........|
       0x0010 0000 0000                                |....|

 25140 foo      GIO   fd 4 read 0 bytes
       ""
 25140 foo      RET   kevent 0
 25140 foo      CALL  kevent(0x4,0xbfbfc5b8,0,0xbfbfc5e8,0x1,0)
 25140 foo      GIO   fd 4 wrote 0 bytes
       ""
 25140 foo      RET   kevent -1 errno 4 Interrupted system call
 25140 foo      PSIG  SIGALRM caught handler=0x285147b0 mask=0x80000000 code=0x0
 25140 foo      CALL  sigreturn(0xbfbfc290)
 25140 foo      RET   sigreturn JUSTRETURN

Apparently something in the GHC runtime is causing this SIGALARM, which
interrupts the kevent() call, rather than letting it wait for an event.
Other than that, the straces *seem* the same to me, leading me to believe
I've not gotten something wrong in my haskell code.

I wonder if this bug also exists on regular FreeBSD?

-- System Information:
Debian Release: wheezy/sid
  APT prefers unstable
  APT policy: (500, 'unstable')
Architecture: kfreebsd-i386

Kernel: GNU/kFreeBSD fischer 8.1-1-686-smp #0 Fri Oct 21 21:08:56 UTC 2011 i686 i386 QEMU Virtual CPU version 0.12.5 GNU/kFreeBSD

-- 
see shy jo
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