October 2018 - ghc-tickets

[GHC] #14510: GHC.ExecutionStack.showStackTrace broken
by GHC 03 Mar '19

03 Mar '19

#14510: GHC.ExecutionStack.showStackTrace broken -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- When compiled with the dwarf bindist of 8.2.2 with {{{ ghc --make -g testdwarf.hs }}} The following is output: {{{ testdwarf: Failed to get stack frames of current process: no matching address range: Success }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14510> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14999: unwinding info for stg_catch_frame is wrong
by GHC 03 Mar '19

03 Mar '19

#14999: unwinding info for stg_catch_frame is wrong -------------------------------------+------------------------------------- Reporter: niteria | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.4.3 Component: Compiler | Version: Keywords: | Operating System: Linux Architecture: x86_64 | Type of failure: Debugging (amd64) | information is incorrect Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Minimized `stg_catch_frame` (`Small.cmm`): {{{ #define CATCH_FRAME 34 #define SIZEOF_StgCatchFrame (SIZEOF_StgHeader+16) INFO_TABLE_RET(stg_catch_frame, CATCH_FRAME, bits64 info_ptr, bits64 exceptions_blocked, gcptr handler) return (gcptr ret) { unwind Sp = Sp + SIZEOF_StgCatchFrame; return (ret); } }}} Compile `"inplace/bin/ghc-stage2" -O2 -g -c Small.cmm` using GHC HEAD. `objdump -D` for `stg_catch_frame_info`: {{{ 0000000000000010 <stg_catch_frame_info>: 10: 48 83 c5 18 add $0x18,%rbp 14: ff 65 00 jmpq *0x0(%rbp) }}} `readelf --debug-dump=frames-interp Small.o`: {{{ Contents of the .debug_frame section: 00000000 0000000000000014 ffffffff CIE "" cf=1 df=-8 ra=16 LOC CFA rbp rsp ra 0000000000000000 rbp+0 v+0 s c+0 00000018 000000000000002c 00000000 FDE cie=00000000 pc=000000000000000f..0000000000000017 LOC CFA rbp rsp ra 000000000000000f rbp+0 v+0 s c+0 000000000000000f rbp+24 v+0 s c+0 0000000000000010 rbp+0 v+0 s c+0 }}} **How do I know this is wrong?** http://www.dwarfstd.org/doc/dwarf-2.0.0.pdf has a nice example in Appendix 5 (page 101 of the pdf). The question that I had was if the CFA value at LOC is after or before the instruction at LOC executes. Appendix 5 clearly shows that it's **before**. Hence for LOC = 0x10 here CFA shouldn't have changed. It can and should change at LOC = 0x14. For comparison this is what `8.0.2` produced (and it worked more often): {{{ 0000000000000010 <stg_catch_frame_info>: 10: 48 83 c5 18 add $0x18,%rbp 14: ff 65 00 jmpq *0x0(%rbp) }}} {{{ Contents of the .debug_frame section: 00000000 0000000000000014 ffffffff CIE "" cf=1 df=-8 ra=16 LOC CFA rbp rsp ra 0000000000000000 rbp+0 v+0 s c+0 00000018 0000000000000024 00000000 FDE cie=00000000 pc=000000000000000f..0000000000000017 LOC CFA rbp rsp ra 000000000000000f rbp+0 v+0 s c+0 000000000000000f rbp+24 v+0 s c+0 }}} Debugging follows in the comments. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14999> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14894: HEAD fails to build with -g1
by GHC 03 Mar '19

03 Mar '19

#14894: HEAD fails to build with -g1 -------------------------------------+------------------------------------- Reporter: niteria | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.5 Keywords: | Operating System: Unknown/Multiple Architecture: x86_64 | Type of failure: Debugging (amd64) | information is incorrect Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I wanted to see how `-g1` vs `-g2` impact compile speed. Unfortunately I get linking errors trying to build GHC with `-g`. Steps: 1) Add {{{ GhcLibHcOpts += -g1 GhcRtsHcOpts += -g1 }}} to `mk/build.mk`. I used devel2 flavor. 2) `./boot && ./configure && make -j` 3) Observe failure The failure (trimmed): {{{ /data/users/bnitka/ghc-HEAD-dwarf-lint-fixes-g/libraries/base/dist- install/build/libHSbase-4.11.0.0.a(Internals.o)(.debug_info+0x1c94): error: undefined refe rence to '.LcbG2_info_die' /data/users/bnitka/ghc-HEAD-dwarf-lint-fixes-g/libraries/base/dist- install/build/libHSbase-4.11.0.0.a(Internals.o)(.debug_info+0x1cc7): error: undefined refe rence to '.LcbGL_die' /data/users/bnitka/ghc-HEAD-dwarf-lint-fixes-g/libraries/base/dist- install/build/libHSbase-4.11.0.0.a(Internals.o)(.debug_info+0x1cfa): error: undefined refe rence to '.LcbI0_die' /data/users/bnitka/ghc-HEAD-dwarf-lint-fixes-g/libraries/base/dist- install/build/libHSbase-4.11.0.0.a(Internals.o)(.debug_info+0x1d2d): error: undefined refe rence to '.LcbIh_die' /data/users/bnitka/ghc-HEAD-dwarf-lint-fixes-g/libraries/base/dist- install/build/libHSbase-4.11.0.0.a(Internals.o)(.debug_info+0x21a4): error: undefined refe rence to '.LcbSn_info_die' /data/users/bnitka/ghc-HEAD-dwarf-lint-fixes-g/libraries/base/dist- install/build/libHSbase-4.11.0.0.a(Internals.o)(.debug_info+0x21d1): error: undefined refe rence to '.LcbTc_die' /data/users/bnitka/ghc-HEAD-dwarf-lint-fixes-g/libraries/base/dist- install/build/libHSbase-4.11.0.0.a(Internals.o)(.debug_info+0x234f): error: undefined refe rence to '.Lcc18_die' /data/users/bnitka/ghc-HEAD-dwarf-lint-fixes-g/libraries/base/dist- install/build/libHSbase-4.11.0.0.a(Internals.o)(.debug_info+0x2c76): error: undefined refe rence to '.Lccmj_info_die' /data/users/bnitka/ghc-HEAD-dwarf-lint-fixes-g/libraries/base/dist- install/build/libHSbase-4.11.0.0.a(Internals.o)(.debug_info+0x2dff): error: undefined refe rence to '.LccsV_die' /data/users/bnitka/ghc-HEAD-dwarf-lint-fixes-g/libraries/base/dist- install/build/libHSbase-4.11.0.0.a(Internals.o)(.debug_info+0x2e2f): error: undefined refe rence to '.Lcct6_info_die' /data/users/bnitka/ghc-HEAD-dwarf-lint-fixes-g/libraries/base/dist- install/build/libHSbase-4.11.0.0.a(Internals.o)(.debug_info+0x2f38): error: undefined refe rence to '.Lccv1_info_die' /data/users/bnitka/ghc-HEAD-dwarf-lint-fixes-g/libraries/base/dist- install/build/libHSbase-4.11.0.0.a(Internals.o)(.debug_info+0x2f66): error: undefined refe rence to '.Lccve_die' }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14894> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14834: Executable have problems with DWARF debug information
by GHC 03 Mar '19

03 Mar '19

#14834: Executable have problems with DWARF debug information -------------------------------------+------------------------------------- Reporter: varosi | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 (Debugging) | Keywords: | Operating System: Windows Architecture: x86_64 | Type of failure: Debugging (amd64) | information is incorrect Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- We're compiling production code with GHC 8.2.2 under Windows 10 (i.e. Mingw64). A crash occured during one of our FFI bindings and we wanted to use latest GHC debugging functionallity to find the problem faster. We used a tool cv2pdb to convert DWARF information into PDB, but we hit a crash with the tool - [https://github.com/rainers/cv2pdb/issues/23] In response, the tool author brought us back a output of a problem in objdump tool over our executable: {{{ c:\tmp\cv\crash>C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe -W crash.exe >objdump C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: Encoded value extends past end of section C:\l\d\GDC-2.068\bin\x86_64-unknown-linux-gnu-objdump.exe: Warning: There is a hole [0x682a - 0x6867] in .debug_loc section. }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14834> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15117: Add linting checks for DWARF unwind information
by GHC 03 Mar '19

03 Mar '19

#15117: Add linting checks for DWARF unwind information -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.2.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- DWARF unwind information is rather subtle and needs to be manually specified in some cases. Having at least some basic sanity checks would hep prevent against things like #14999. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15117> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15179: Unwinding info for stg_ap_v_info is wrong
by GHC 03 Mar '19

03 Mar '19

#15179: Unwinding info for stg_ap_v_info is wrong -------------------------------------+------------------------------------- Reporter: niteria | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.5 (Debugging) | Keywords: | Operating System: Linux Architecture: | Type of failure: Debugging Unknown/Multiple | information is incorrect Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The `readelf --debug-dump=frames-interp` output for `stg_ap_v_info` is: {{{ 00000018 0000000000000034 00000000 FDE cie=00000000 pc=000000000000000f..000000000000021d LOC CFA rbp rsp ra 000000000000000f rbp+0 v+0 u c+0 0000000000000037 rbp+0 v+0 vexp c+0 0000000000000047 rbp+0 v+0 s c+0 }}} It's wrong because it unwinds to the same frame, see `cfa = rbp + 0`. I know the reason, I will put it in the comments below. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15179> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15207: bad dwarf frame in stgRun.c when compiled with with gcc on mac and assembled by as/gcc/clang (aka apple clang assembler)
by GHC 03 Mar '19

03 Mar '19

#15207: bad dwarf frame in stgRun.c when compiled with with gcc on mac and assembled by as/gcc/clang (aka apple clang assembler) ----------------------------------------+--------------------------------- Reporter: carter | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Runtime System | Version: 8.4.3 Keywords: | Operating System: MacOS X Architecture: Unknown/Multiple | Type of failure: None/Unknown Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: ----------------------------------------+--------------------------------- for current master, if i build on a mac / OSX high sierra environment with CC set as any flavor of recent GCC rather than apple clang, i get a failure "no open frame" when as (aka apple clang / apple llvm acting as the assembler) is run on the .s file produced by stgRun.c (rts/StgCRun.c to be exact) this error message seems to come from https://github.com/llvm- mirror/llvm/blob/da4a2839d80ac52958be0129b871beedfe90136e/lib/MC/MCStreamer.cpp#L221 https://gist.github.com/cartazio/8cbfb3305e1daa4f7ffc3f6bb90a2891 has the gcc and clang style assembly for /usr/local/bin/gcc-8 -fno-stack-protector -DTABLES_NEXT_TO_CODE -Iincludes -Iincludes/dist -Iincludes/dist-derivedconstants/header -Iincludes/dist- ghcconstants/header -Irts -Irts/dist/build -Irts/dist/build -Irts/dist/build/./autogen -fno-common -U__PIC__ -D__PIC__ -x assembler -c /var/folders/py/wgp_hj9d2rl3cx48yym_ynj00000gn/T/ghc22029_0/ghc_1.s -o rts/dist/build/StgCRun.debug_o this is example asm for the the debug way -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15207> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #15461: Machine accessible interface to GHCi
by GHC 03 Mar '19

03 Mar '19

#15461: Machine accessible interface to GHCi -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: 8.6.1 Component: GHCi | Version: 8.4.3 Keywords: newcomer | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- For a long time tooling users (e.g. `haskell-mode`) have been treating GHCi as a language server. As one would expect this leads to a frustrating situation for both GHC developers (who feel constrained in their ability to change output) and users (who occasionally suffer breakage, e.g. [[https://github.com/haskell/haskell- mode/issues/1553#issuecomment-409267399]]). Ultimately the solution seems fairly clear: 1. allow GHCi to expose multiple REPL interfaces (e.g. such that a user could have multiple textual REPLs open, all served by the same GHCi session) 2. add a machine-readable request protocol to GHCi, giving tooling users a way to use GHCi's functionality without parsing human-readable output (1) should be fairly straightforward to implement. (2) on the other hand requires some design work (e.g. what does the wire protocol look like?) and a fair bit of refactoring (to expose the existing commands in a machine-readable manner). -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15461> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14494: TBQueue leaks space under certain workloads
by GHC 03 Mar '19

03 Mar '19

#14494: TBQueue leaks space under certain workloads -------------------------------------+------------------------------------- Reporter: arybczak | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: libraries | Version: 8.2.1 (other) | Keywords: stm | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I'm using TBQueue and I noticed suspiciously high memory usage, so I decided to profile and it turned out that readTBQueue leaks space (see attached before.png). After closer inspection it turned out it's the `writeTVar rsize (r + 1)` in readTBQueue definition that's the problem - after substitution it for `writeTVar rsize $! r + 1` the leak is gone (see attached after.png) Here are -s outputs: Before: {{{ 366,535,518,024 bytes allocated in the heap 115,643,281,224 bytes copied during GC 241,356,416 bytes maximum residency (1182 sample(s)) 1,516,944 bytes maximum slop 392 MB total memory in use (0 MB lost due to fragmentation) Tot time (elapsed) Avg pause Max pause Gen 0 247273 colls, 247273 par 128.854s 28.654s 0.0001s 0.0182s Gen 1 1182 colls, 1181 par 352.162s 87.812s 0.0743s 0.1322s Parallel GC work balance: 78.17% (serial 0%, perfect 100%) TASKS: 24 (1 bound, 16 peak workers (23 total), using -N4) SPARKS: 0 (0 converted, 0 overflowed, 0 dud, 0 GC'd, 0 fizzled) INIT time 0.003s ( 0.003s elapsed) MUT time 581.754s (226.191s elapsed) GC time 317.130s ( 75.533s elapsed) RP time 0.000s ( 0.000s elapsed) PROF time 163.885s ( 40.933s elapsed) EXIT time 0.013s ( 0.011s elapsed) Total time 1062.789s (301.738s elapsed) Alloc rate 630,052,684 bytes per MUT second Productivity 54.7% of total user, 61.4% of total elapsed gc_alloc_block_sync: 8998531 whitehole_spin: 96 gen[0].sync: 180553 gen[1].sync: 31648044 }}} After: {{{ 431,671,260,464 bytes allocated in the heap 86,540,207,400 bytes copied during GC 170,338,336 bytes maximum residency (1381 sample(s)) 1,159,472 bytes maximum slop 260 MB total memory in use (0 MB lost due to fragmentation) Tot time (elapsed) Avg pause Max pause Gen 0 290179 colls, 290179 par 148.921s 33.097s 0.0001s 0.0217s Gen 1 1381 colls, 1380 par 206.679s 51.492s 0.0373s 0.0528s Parallel GC work balance: 75.51% (serial 0%, perfect 100%) TASKS: 23 (1 bound, 17 peak workers (22 total), using -N4) SPARKS: 0 (0 converted, 0 overflowed, 0 dud, 0 GC'd, 0 fizzled) INIT time 0.005s ( 0.004s elapsed) MUT time 681.718s (241.009s elapsed) GC time 258.643s ( 60.370s elapsed) RP time 0.000s ( 0.000s elapsed) PROF time 96.957s ( 24.219s elapsed) EXIT time 0.009s ( 0.007s elapsed) Total time 1037.335s (301.390s elapsed) Alloc rate 633,210,748 bytes per MUT second Productivity 65.7% of total user, 71.9% of total elapsed gc_alloc_block_sync: 5494680 whitehole_spin: 184 gen[0].sync: 184109 gen[1].sync: 24223953 }}} Attached patch fixes the problem (I made all Int increments/decrements in the module strict as there is no need for them to be lazy). -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14494> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10841: Run handler on STM retry
by GHC 03 Mar '19

03 Mar '19

#10841: Run handler on STM retry -------------------------------------+------------------------------------- Reporter: shlevy | Owner: Type: feature | Status: new request | Priority: normal | Milestone: Component: libraries | Version: 7.10.2 (other) | Keywords: stm | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- It would be nice to have a function like: {{{#!hs -- | Perform a series of STM actions atomically. -- -- Whenever the transaction retries, run the handler. If it doesn't return 'Nothing', -- stop the retrying and return the value given by the handler. atomicallyWithRetryHandler :: STM a -> IO (Maybe a) -> IO a }}} This would allow tracking retry statistics, printing debug messages on each retry, etc. without resorting to unsafeIOToSTM which can't safely do things like printing. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10841> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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