https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101037
Bug ID: 101037
Summary: std::atomic_flag deadlock on Windows
Product: gcc
Version: 11.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: bjornsundin02 at gmail dot com
Target Milestone: ---
The attached preprocessed file is a "ping-pong" example where two threads take
turns to wait for the other thread using a C++20 std::atomic_flag. I am fairly
certain that the code is correct and should not hang. I tested the program on
Linux (Ubuntu 21.04), where it works as expected every time. On Windows, with a
build from https://winlibs.com/, it more often than not hangs. The program on
Windows is compiled in exactly the same way as on Linux.
The expected behavior is: the program exits within less than a second.
The observed behavior is: sometimes the program exits within less than a
second, but often it hangs without ever returning.
Below is the complete compiler command and output:
> g++ -v -save-temps -std=c++20 -pthread deadlock_debugging.cpp
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=c:/mingw64/bin/../libexec/gcc/x86_64-w64-mingw32/11.1.1/lto-wrapper.exe
OFFLOAD_TARGET_NAMES=nvptx-none
Target: x86_64-w64-mingw32
Configured with: ../configure
--prefix=/R/winlibs64_stage/inst_gcc-11-20210605/share/gcc
--build=x86_64-w64-mingw32 --host=x86_64-w64-mingw32
--enable-offload-targets=nvptx-none --with-pkgversion='MinGW-W64
x86_64-posix-seh, built by Brecht Sanders' --with-tune=generic
--enable-checking=release --enable-threads=posix --disable-sjlj-exceptions
--disable-libunwind-exceptions
--disable-serial-configure --disable-bootstrap --enable-host-shared
--enable-plugin --disable-default-ssp --disable-rpath --enable-libstdcxx-pch
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--enable-libstdcxx --enable-lto --enable-fully-dynamic-string --enable-libgomp
--enable-graphite --enable-mingw-wildcard
--with-mpc=/d/Prog/winlibs64_stage/custombuilt
--with-mpfr=/d/Prog/winlibs64_stage/custombuilt
--with-gmp=/d/Prog/winlibs64_stage/custombuilt
--with-isl=/d/Prog/winlibs64_stage/custombuilt --enable-install-libiberty
--enable-__cxa_atexit --without-included-gettext --with-diagnostics-color=auto
--enable-clocale=generic --with-libiconv --with-system-zlib
--with-build-sysroot=/R/winlibs64_stage/gcc-11-20210605/build_mingw/mingw-w64
CFLAGS=-I/d/Prog/winlibs64_stage/custombuilt/include/libdl-win32
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 11.1.1 20210605 (MinGW-W64 x86_64-posix-seh, built by Brecht
Sanders)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-std=c++20' '-pthread' '-shared-libgcc'
'-mtune=generic' '-march=x86-64' '-dumpdir' 'a-'
c:/mingw64/bin/../libexec/gcc/x86_64-w64-mingw32/11.1.1/cc1plus.exe -E -quiet
-v -iprefix c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/11.1.1/ -D_REENTRANT
-U_REENTRANT deadlock_debugging.cpp -mtune=generic -march=x86-64 -std=c++20
-fpch-preprocess -o a-deadlock_debugging.ii
ignoring duplicate directory
"c:/mingw64/lib/gcc/../../lib/gcc/x86_64-w64-mingw32/11.1.1/../../../../include/c++/11.1.1"
ignoring duplicate directory
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ignoring duplicate directory
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ignoring duplicate directory
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ignoring nonexistent directory
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ignoring nonexistent directory
"/R/winlibs64_stage/inst_gcc-11-20210605/share/gcc/include"
ignoring duplicate directory
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ignoring duplicate directory
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ignoring nonexistent directory "/mingw/include"
#include "..." search starts here:
#include <...> search starts here:
c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/11.1.1/../../../../include/c++/11.1.1
c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/11.1.1/../../../../include/c++/11.1.1/x86_64-w64-mingw32
c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/11.1.1/../../../../include/c++/11.1.1/backward
c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/11.1.1/include
c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/11.1.1/../../../../include
c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/11.1.1/include-fixed
c:\mingw64\bin\../lib/gcc/x86_64-w64-mingw32/11.1.1/../../../../x86_64-w64-mingw32/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-std=c++20' '-pthread' '-shared-libgcc'
'-mtune=generic' '-march=x86-64' '-dumpdir' 'a-'
c:/mingw64/bin/../libexec/gcc/x86_64-w64-mingw32/11.1.1/cc1plus.exe
-fpreprocessed a-deadlock_debugging.ii -quiet -dumpdir a- -dumpbase
deadlock_debugging.cpp -dumpbase-ext .cpp -mtune=generic -march=x86-64
-std=c++20 -version -o a-deadlock_debugging.s
GNU C++20 (MinGW-W64 x86_64-posix-seh, built by Brecht Sanders) version 11.1.1
20210605 (x86_64-w64-mingw32)
compiled by GNU C version 11.1.1 20210605, GMP version 6.2.1, MPFR
version 4.1.0, MPC version 1.2.1, isl version isl-0.24-GMP
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
GNU C++20 (MinGW-W64 x86_64-posix-seh, built by Brecht Sanders) version 11.1.1
20210605 (x86_64-w64-mingw32)
compiled by GNU C version 11.1.1 20210605, GMP version 6.2.1, MPFR
version 4.1.0, MPC version 1.2.1, isl version isl-0.24-GMP
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 15f4039a47217655d2f44ccd07e6db0b
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-std=c++20' '-pthread' '-shared-libgcc'
'-mtune=generic' '-march=x86-64' '-dumpdir' 'a-'
c:/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/11.1.1/../../../../x86_64-w64-mingw32/bin/as.exe
-v -o a-deadlock_debugging.o a-deadlock_debugging.s
GNU assembler version 2.36.1 (x86_64-w64-mingw32) using BFD version (Binutils
for MinGW-W64 x86_64, built by Brecht Sanders) 2.36.1
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LIBRARY_PATH=c:/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/11.1.1/;c:/mingw64/bin/../lib/gcc/;c:/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/11.1.1/../../../../x86_64-w64-mingw32/lib/../lib/;c:/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/11.1.1/../../../../lib/;c:/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/11.1.1/../../../../x86_64-w64-mingw32/lib/;c:/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/11.1.1/../../../
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c:/mingw64/bin/../lib/gcc/x86_64-w64-mingw32/11.1.1/crtend.o
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-std=c++20' '-pthread' '-shared-libgcc'
'-mtune=generic' '-march=x86-64' '-dumpdir' 'a.'
