On Wed, Sep 16, 2026 at 5:09 PM Jonathan Wakely <[email protected]> wrote:
> Port the testsuite's simple semaphore type to use POSIX semaphores when
> System V semaphores are not supported, as the latter are part of the XSI
> option and not mandated by POSIX. For the POSIX semaphore path we need
> to use mmap to create the semaphore in shared memory and also need to
> handle older systems without MAP_ANONYMOUS support. We need to use
> unnamed semaphores because using sem_open to create a named semaphore
> requires creating two or more unique names per test that work even when
> the tests are run in parallel.
>
> Although it might make sense to prefer the new path and use POSIX
> semaphores by default, but macOS defines _POSIX_SEMAPHORES to a positive
> value but its sem_init always returns ENOSYS at runtime. Instead of
> trying that and then switching to shmget as a runtime fallback, we might
> as well just continue using the code that we know works fine - i.e. the
> SysV semaphore implementation.
>
> For the case where neither SysV nor POSIX semaphores are available, make
> the __gnu_test::semaphore constructor abort, so the tests FAIL instead
> of silently PASS.
>
> Move the definition of the semaphore to a new header, so that it's only
> defined in the handful of tests that actually use it, and the
> definitions of the member functions to a new file.
>
> Also add a dejagnu dg-require-sysv-or-posix-semaphore directive so that
> tests which don't support either type of semaphore will be UNSUPPORTED
> instead of PASS (or FAIL with the new aborting constructor). This test
> uses _XOPEN_UNIX rather than the three autoconf macros that are checked
> in testsuite_semaphore.cc but that is a reasonable proxy for SysV
> semaphore support. It might mean that some very old systems mark those
> tests as UNSUPPORTED when they do actually support the SysV semaphores
> without defining the _XOPEN_UNIX macro. I can live with that.
>
> libstdc++-v3/ChangeLog:
>
> PR libstdc++/127425
> * doc/xml/manual/test.xml: Document new testsuite header.
> * doc/html/manual/test.html: Regenerate.
> * testsuite/27_io/basic_filebuf/close/char/4879.cc: Use new
> dg-require-sysv-or-posix-semaphore directive.
> * testsuite/27_io/basic_filebuf/close/char/9964.cc: Likewise.
> * testsuite/27_io/basic_filebuf/imbue/char/13171-2.cc: Likewise.
> * testsuite/27_io/basic_filebuf/imbue/wchar_t/14975-2.cc:
> Likewise.
> * testsuite/27_io/basic_filebuf/seekoff/char/26777.cc: Likewise.
> * testsuite/27_io/basic_filebuf/underflow/char/10097.cc:
> Likewise.
> * testsuite/27_io/objects/char/7.cc: Likewise.
> * testsuite/27_io/objects/char/9661-1.cc: Likewise.
> * testsuite/27_io/objects/wchar_t/7.cc: Likewise.
> * testsuite/27_io/objects/wchar_t/9661-1.cc: Likewise.
> * testsuite/lib/dg-options.exp
> (dg-require-sysv-or-posix-semaphore): New proc.
> * testsuite/lib/libstdc++.exp (v3-build_support): Add new file
> to list of testsuite source files.
> (check_v3_target_posix_or_sysv_semaphore): New proc.
> * testsuite/util/testsuite_hooks.cc (semaphore): Move to new
> file.
> * testsuite/util/testsuite_hooks.h (semaphore): Likewise.
> * testsuite/util/testsuite_semaphore.cc: Move definition of
> semaphore member functions here. Fix resource leak in
> constructor if semctl fails. Prefer to use mmap+sem_init instead
> of semget+semctl.
> * testsuite/util/testsuite_semaphore.h: Move definition of
> semaphore to here.
> ---
>
> Tested 27_io/* on x86_64-linux and the rest of the testsuite is running
> now.
>
One comment regarding a missing unmap in the error path, and an update to
the comment.
Otherwise LGTM.
>
> libstdc++-v3/doc/html/manual/test.html | 6 +-
> libstdc++-v3/doc/xml/manual/test.xml | 8 +
> .../27_io/basic_filebuf/close/char/4879.cc | 2 +
> .../27_io/basic_filebuf/close/char/9964.cc | 2 +
> .../27_io/basic_filebuf/imbue/char/13171-2.cc | 2 +
> .../basic_filebuf/imbue/wchar_t/14975-2.cc | 2 +
> .../27_io/basic_filebuf/seekoff/char/26777.cc | 2 +
> .../basic_filebuf/underflow/char/10097.cc | 2 +
> .../testsuite/27_io/objects/char/7.cc | 2 +
> .../testsuite/27_io/objects/char/9661-1.cc | 2 +
> .../testsuite/27_io/objects/wchar_t/7.cc | 2 +
> .../testsuite/27_io/objects/wchar_t/9661-1.cc | 2 +
> libstdc++-v3/testsuite/lib/dg-options.exp | 9 ++
> libstdc++-v3/testsuite/lib/libstdc++.exp | 11 ++
> .../testsuite/util/testsuite_hooks.cc | 96 -----------
> libstdc++-v3/testsuite/util/testsuite_hooks.h | 24 ---
> .../testsuite/util/testsuite_semaphore.cc | 153 ++++++++++++++++++
> .../testsuite/util/testsuite_semaphore.h | 62 +++++++
> 18 files changed, 268 insertions(+), 121 deletions(-)
> create mode 100644 libstdc++-v3/testsuite/util/testsuite_semaphore.cc
> create mode 100644 libstdc++-v3/testsuite/util/testsuite_semaphore.h
>
> diff --git a/libstdc++-v3/doc/html/manual/test.html
> b/libstdc++-v3/doc/html/manual/test.html
> index 404d7ddbf879..1db7dd5bcae7 100644
> --- a/libstdc++-v3/doc/html/manual/test.html
> +++ b/libstdc++-v3/doc/html/manual/test.html
> @@ -647,7 +647,11 @@ only default variables.
> </p><p>
> A number of class abstractions for performance counters, and
> reporting functions including:
> - </p><div class="itemizedlist"><ul class="itemizedlist"
> style="list-style-type: circle; "><li
> class="listitem"><p>time_counter</p></li><li
> class="listitem"><p>resource_counter</p></li><li
> class="listitem"><p>report_performance</p></li></ul></div></li></ul></div></div></div><div
> class="section"><div class="titlepage"><div><div><h3 class="title"><a
> id="test.special"></a>Special Topics</h3></div></div></div><div
> class="section"><div class="titlepage"><div><div><h4 class="title"><a
> id="test.exception.safety"></a>
> + </p><div class="itemizedlist"><ul class="itemizedlist"
> style="list-style-type: circle; "><li
> class="listitem"><p>time_counter</p></li><li
> class="listitem"><p>resource_counter</p></li><li
> class="listitem"><p>report_performance</p></li></ul></div></li><li
> class="listitem"><p>
> + <span class="emphasis"><em>testsuite_semaphore.h</em></span>
> + </p><p>
> + A simple binary semaphore used for some multi-process I/O tests.
> + </p></li></ul></div></div></div><div class="section"><div
> class="titlepage"><div><div><h3 class="title"><a
> id="test.special"></a>Special Topics</h3></div></div></div><div
> class="section"><div class="titlepage"><div><div><h4 class="title"><a
> id="test.exception.safety"></a>
> Qualifying Exception Safety Guarantees
> <a id="id-1.3.6.3.5.7.2.1.1.1" class="indexterm"></a>
> </h4></div></div></div><div class="section"><div
> class="titlepage"><div><div><h5 class="title"><a
> id="test.exception.safety.overview"></a>Overview</h5></div></div></div><p>
> diff --git a/libstdc++-v3/doc/xml/manual/test.xml
> b/libstdc++-v3/doc/xml/manual/test.xml
> index 68b5f8aedb41..f5c441bd9413 100644
> --- a/libstdc++-v3/doc/xml/manual/test.xml
> +++ b/libstdc++-v3/doc/xml/manual/test.xml
> @@ -1081,6 +1081,14 @@ only default variables.
> <listitem><para>report_performance</para></listitem>
> </itemizedlist>
> </listitem>
> + <listitem>
> + <para>
> + <emphasis>testsuite_semaphore.h</emphasis>
> + </para>
> + <para>
> + A simple binary semaphore used for some multi-process I/O tests.
> + </para>
> + </listitem>
> </itemizedlist>
> </section>
>
> diff --git a/libstdc++-v3/testsuite/27_io/basic_filebuf/close/char/4879.cc
> b/libstdc++-v3/testsuite/27_io/basic_filebuf/close/char/4879.cc
> index 3e0b134edb95..5246a33e8493 100644
> --- a/libstdc++-v3/testsuite/27_io/basic_filebuf/close/char/4879.cc
> +++ b/libstdc++-v3/testsuite/27_io/basic_filebuf/close/char/4879.cc
> @@ -1,5 +1,6 @@
> // { dg-require-fork "" }
> // { dg-require-mkfifo "" }
> +// { dg-require-sysv-or-posix-semaphore "" }
>
> // Copyright (C) 2001-2026 Free Software Foundation, Inc.
> //
> @@ -33,6 +34,7 @@
> #include <sys/stat.h>
>
> #include <testsuite_hooks.h>
> +#include <testsuite_semaphore.h>
>
> // libstdc++/2913, libstdc++/4879
> // John Fardo <[email protected]>, Brad Garcia <[email protected]>
> diff --git a/libstdc++-v3/testsuite/27_io/basic_filebuf/close/char/9964.cc
> b/libstdc++-v3/testsuite/27_io/basic_filebuf/close/char/9964.cc
> index ba864fa7e9e8..84b406ac0727 100644
> --- a/libstdc++-v3/testsuite/27_io/basic_filebuf/close/char/9964.cc
> +++ b/libstdc++-v3/testsuite/27_io/basic_filebuf/close/char/9964.cc
> @@ -1,5 +1,6 @@
> // { dg-require-fork "" }
> // { dg-require-mkfifo "" }
> +// { dg-require-sysv-or-posix-semaphore "" }
>
> // Copyright (C) 2001-2026 Free Software Foundation, Inc.
> //
> @@ -32,6 +33,7 @@
> #include <sys/stat.h>
>
> #include <testsuite_hooks.h>
> +#include <testsuite_semaphore.h>
>
> // libstdc++/9964
> bool test_07()
> diff --git
> a/libstdc++-v3/testsuite/27_io/basic_filebuf/imbue/char/13171-2.cc
> b/libstdc++-v3/testsuite/27_io/basic_filebuf/imbue/char/13171-2.cc
> index 5a42e18834b0..210efae9a98a 100644
> --- a/libstdc++-v3/testsuite/27_io/basic_filebuf/imbue/char/13171-2.cc
> +++ b/libstdc++-v3/testsuite/27_io/basic_filebuf/imbue/char/13171-2.cc
> @@ -2,6 +2,7 @@
> // { dg-require-namedlocale "en_US.ISO8859-1" }
> // { dg-require-fork "" }
> // { dg-require-mkfifo "" }
> +// { dg-require-sysv-or-posix-semaphore "" }
>
> // Copyright (C) 2003-2026 Free Software Foundation, Inc.
> //
> @@ -30,6 +31,7 @@
> #include <sys/stat.h>
>
> #include <testsuite_hooks.h>
> +#include <testsuite_semaphore.h>
>
> // libstdc++/13171
> bool test01()
> diff --git
> a/libstdc++-v3/testsuite/27_io/basic_filebuf/imbue/wchar_t/14975-2.cc
> b/libstdc++-v3/testsuite/27_io/basic_filebuf/imbue/wchar_t/14975-2.cc
> index f4dadd917ee9..886b7d66053b 100644
> --- a/libstdc++-v3/testsuite/27_io/basic_filebuf/imbue/wchar_t/14975-2.cc
> +++ b/libstdc++-v3/testsuite/27_io/basic_filebuf/imbue/wchar_t/14975-2.cc
> @@ -1,6 +1,7 @@
> // { dg-require-namedlocale "en_US.ISO8859-1" }
> // { dg-require-fork "" }
> // { dg-require-mkfifo "" }
> +// { dg-require-sysv-or-posix-semaphore "" }
>
> // 2004-04-16 Petur Runolfsson <[email protected]>
>
> @@ -31,6 +32,7 @@
> #include <sys/stat.h>
>
> #include <testsuite_hooks.h>
> +#include <testsuite_semaphore.h>
>
> // libstdc++/14975
> bool test01()
> diff --git
> a/libstdc++-v3/testsuite/27_io/basic_filebuf/seekoff/char/26777.cc
> b/libstdc++-v3/testsuite/27_io/basic_filebuf/seekoff/char/26777.cc
> index b003090f920c..1931db09ad04 100644
> --- a/libstdc++-v3/testsuite/27_io/basic_filebuf/seekoff/char/26777.cc
> +++ b/libstdc++-v3/testsuite/27_io/basic_filebuf/seekoff/char/26777.cc
> @@ -1,5 +1,6 @@
> // { dg-require-fork "" }
> // { dg-require-mkfifo "" }
> +// { dg-require-sysv-or-posix-semaphore "" }
>
> // 2006-03-22 Paolo Carlini <[email protected]>
>
> @@ -21,6 +22,7 @@
> // <http://www.gnu.org/licenses/>.
>
> #include <testsuite_hooks.h>
> +#include <testsuite_semaphore.h>
> #include <fstream>
> #include <sstream>
> #include <cstdlib>
> diff --git
> a/libstdc++-v3/testsuite/27_io/basic_filebuf/underflow/char/10097.cc
> b/libstdc++-v3/testsuite/27_io/basic_filebuf/underflow/char/10097.cc
> index e7c9a91aca04..c320b99920bd 100644
> --- a/libstdc++-v3/testsuite/27_io/basic_filebuf/underflow/char/10097.cc
> +++ b/libstdc++-v3/testsuite/27_io/basic_filebuf/underflow/char/10097.cc
> @@ -1,5 +1,6 @@
> // { dg-require-fork "" }
> // { dg-require-mkfifo "" }
> +// { dg-require-sysv-or-posix-semaphore "" }
>
> // 2001-05-21 Benjamin Kosnik <[email protected]>
>
> @@ -31,6 +32,7 @@
> #include <sys/stat.h>
>
> #include <testsuite_hooks.h>
> +#include <testsuite_semaphore.h>
>
> class UnderBuf : public std::filebuf
> {
> diff --git a/libstdc++-v3/testsuite/27_io/objects/char/7.cc
> b/libstdc++-v3/testsuite/27_io/objects/char/7.cc
> index b5e6fe5b6d7b..2edcf56f7889 100644
> --- a/libstdc++-v3/testsuite/27_io/objects/char/7.cc
> +++ b/libstdc++-v3/testsuite/27_io/objects/char/7.cc
> @@ -1,5 +1,6 @@
> // { dg-require-fork "" }
> // { dg-require-mkfifo "" }
> +// { dg-require-sysv-or-posix-semaphore "" }
>
> // 2003-04-26 Petur Runolfsson <[email protected]>
>
> @@ -31,6 +32,7 @@
> #include <sys/types.h>
> #include <sys/stat.h>
> #include <testsuite_hooks.h>
> +#include <testsuite_semaphore.h>
>
> // Check that cout.flush() is called when last ios_base::Init is
> destroyed.
> bool test07()
> diff --git a/libstdc++-v3/testsuite/27_io/objects/char/9661-1.cc
> b/libstdc++-v3/testsuite/27_io/objects/char/9661-1.cc
> index d9e39cd80c83..9374685969db 100644
> --- a/libstdc++-v3/testsuite/27_io/objects/char/9661-1.cc
> +++ b/libstdc++-v3/testsuite/27_io/objects/char/9661-1.cc
> @@ -1,5 +1,6 @@
> // { dg-require-fork "" }
> // { dg-require-mkfifo "" }
> +// { dg-require-sysv-or-posix-semaphore "" }
>
> // 2003-04-30 Petur Runolfsson <[email protected]>
>
> @@ -21,6 +22,7 @@
> // <http://www.gnu.org/licenses/>.
>
> #include <testsuite_hooks.h>
> +#include <testsuite_semaphore.h>
> #include <cstdio>
> #include <cstdlib>
> #include <iostream>
> diff --git a/libstdc++-v3/testsuite/27_io/objects/wchar_t/7.cc
> b/libstdc++-v3/testsuite/27_io/objects/wchar_t/7.cc
> index 2c03fa1791b9..cc6a2fa3e7d0 100644
> --- a/libstdc++-v3/testsuite/27_io/objects/wchar_t/7.cc
> +++ b/libstdc++-v3/testsuite/27_io/objects/wchar_t/7.cc
> @@ -1,5 +1,6 @@
> // { dg-require-fork "" }
> // { dg-require-mkfifo "" }
> +// { dg-require-sysv-or-posix-semaphore "" }
>
> // 2003-05-01 Petur Runolfsson <[email protected]>
>
> @@ -32,6 +33,7 @@
> #include <sys/stat.h>
>
> #include <testsuite_hooks.h>
> +#include <testsuite_semaphore.h>
>
> // Check that wcout.flush() is called when last ios_base::Init is
> destroyed.
> bool test07()
> diff --git a/libstdc++-v3/testsuite/27_io/objects/wchar_t/9661-1.cc
> b/libstdc++-v3/testsuite/27_io/objects/wchar_t/9661-1.cc
> index f49d010fbf91..f8194aef3eec 100644
> --- a/libstdc++-v3/testsuite/27_io/objects/wchar_t/9661-1.cc
> +++ b/libstdc++-v3/testsuite/27_io/objects/wchar_t/9661-1.cc
> @@ -1,5 +1,6 @@
> // { dg-require-fork "" }
> // { dg-require-mkfifo "" }
> +// { dg-require-sysv-or-posix-semaphore "" }
>
> // 2003-04-30 Petur Runolfsson <[email protected]>
>
> @@ -21,6 +22,7 @@
> // <http://www.gnu.org/licenses/>.
>
> #include <testsuite_hooks.h>
> +#include <testsuite_semaphore.h>
> #include <cstdio>
> #include <cstdlib>
> #include <iostream>
> diff --git a/libstdc++-v3/testsuite/lib/dg-options.exp
> b/libstdc++-v3/testsuite/lib/dg-options.exp
> index 615a57992602..d8f31aae7387 100644
> --- a/libstdc++-v3/testsuite/lib/dg-options.exp
> +++ b/libstdc++-v3/testsuite/lib/dg-options.exp
> @@ -286,6 +286,15 @@ proc dg-require-cpp-feature-test { n args } {
> return
> }
>
> +proc dg-require-sysv-or-posix-semaphore { n args } {
> + if { ![ check_v3_target_posix_or_sysv_semaphore $args ] } {
> + upvar dg-do-what dg-do-what
> + set dg-do-what [list [lindex ${dg-do-what} 0] "N" "P"]
> + return
> + }
> + return
> +}
> +
> proc add_options_for_no_pch { flags } {
> # Remove any inclusion of bits/stdc++.h from the options.
> regsub -all -- "-include bits/stdc...h" $flags "" flags
> diff --git a/libstdc++-v3/testsuite/lib/libstdc++.exp
> b/libstdc++-v3/testsuite/lib/libstdc++.exp
> index cda231246cb0..4a11c9b47dd3 100644
> --- a/libstdc++-v3/testsuite/lib/libstdc++.exp
> +++ b/libstdc++-v3/testsuite/lib/libstdc++.exp
> @@ -835,6 +835,7 @@ proc v3-build_support { } {
> # Build the support objects.
> set source_files [list testsuite_abi.cc testsuite_allocator.cc \
> testsuite_character.cc testsuite_hooks.cc \
> + testsuite_semaphore.cc \
> io/verified_cmd_line_input.cc \
> io/prog_bar.cc performance/time/elapsed_timer.cc
> ]
> foreach f $source_files {
> @@ -1440,6 +1441,16 @@ proc check_v3_target_nprocs { } {
> }]
> }
>
> +# Return 1 if the POSIX REALTIME option or the XSI option is supported
> +# for the current target, 0 otherwise.
> +proc check_v3_target_posix_or_sysv_semaphore { cond } {
> + set name "posix_or_sysv_semaphore"
> + set inc "#include <unistd.h>"
> + set cond "_POSIX_SEMAPHORES > 0 || _XOPEN_UNIX > 0"
> + set result [v3_check_preprocessor_condition $name $cond $inc]
> + return $result
> +}
> +
> # Return 1 if linking with -static-libstdc++ works, 0 otherwise.
> proc check_v3_target_static_libstdcxx { } {
> return [check_v3_target_prop_cached et_static_libstdcxx {
> diff --git a/libstdc++-v3/testsuite/util/testsuite_hooks.cc
> b/libstdc++-v3/testsuite/util/testsuite_hooks.cc
> index 946bd4a3847a..33ce7112701a 100644
> --- a/libstdc++-v3/testsuite/util/testsuite_hooks.cc
> +++ b/libstdc++-v3/testsuite/util/testsuite_hooks.cc
> @@ -36,20 +36,6 @@
> #include <locale>
> #include <cxxabi.h>
>
> -// If we have <sys/types.h>, <sys/ipc.h>, and <sys/sem.h>, then assume
> -// that System V semaphores are available.
> -#if defined(_GLIBCXX_HAVE_SYS_TYPES_H) \
> - && defined(_GLIBCXX_HAVE_SYS_IPC_H) \
> - && defined(_GLIBCXX_HAVE_SYS_SEM_H)
> -#define _GLIBCXX_SYSV_SEM
> -#endif
> -
> -#ifdef _GLIBCXX_SYSV_SEM
> -#include <sys/types.h>
> -#include <sys/ipc.h>
> -#include <sys/sem.h>
> -#endif
> -
> namespace __gnu_test
> {
> #ifdef _GLIBCXX_RES_LIMITS
> @@ -227,88 +213,6 @@ namespace __gnu_test
> unsigned int destructor::_M_count = 0;
> int copy_tracker::next_id_ = 0;
>
> -#ifdef _GLIBCXX_SYSV_SEM
> - // This union is not declared in system headers. Instead, it must
> - // be defined by user programs.
> - union semun
> - {
> - int val;
> - struct semid_ds *buf;
> - unsigned short *array;
> - };
> -#endif
> -
> - semaphore::semaphore()
> - {
> -#ifdef _GLIBCXX_SYSV_SEM
> - // Remember the PID for the process that created the semaphore set
> - // so that only one process will destroy the set.
> - pid_ = getpid();
> -
> - // GLIBC does not define SEM_R and SEM_A.
> -#ifndef SEM_R
> -#define SEM_R 0400
> -#endif
> -
> -#ifndef SEM_A
> -#define SEM_A 0200
> -#endif
> -
> - // Get a semaphore set with one semaphore.
> - sem_set_ = semget(IPC_PRIVATE, 1, SEM_R | SEM_A);
> - if (sem_set_ == -1)
> - std::__throw_runtime_error("could not obtain semaphore set");
> -
> - // Initialize the semaphore.
> - union semun val;
> - val.val = 0;
> - if (semctl(sem_set_, 0, SETVAL, val) == -1)
> - std::__throw_runtime_error("could not initialize semaphore");
> -#else
> - // There are no semaphores on this system. We have no way to mark
> - // a test as "unsupported" at runtime, so we just exit, pretending
> - // that the test passed.
> - exit(0);
> -#endif
> - }
> -
> - semaphore::~semaphore()
> - {
> -#ifdef _GLIBCXX_SYSV_SEM
> - union semun val;
> - val.val = 0; // Avoid uninitialized variable warning.
> - // Destroy the semaphore set only in the process that created it.
> - if (pid_ == getpid())
> - semctl(sem_set_, 0, IPC_RMID, val);
> -#endif
> - }
> -
> - void
> - semaphore::signal()
> - {
> -#ifdef _GLIBCXX_SYSV_SEM
> - struct sembuf op[1] =
> - {
> - { 0, 1, 0 }
> - };
> - if (semop(sem_set_, op, 1) == -1)
> - std::__throw_runtime_error("could not signal semaphore");
> -#endif
> - }
> -
> - void
> - semaphore::wait()
> - {
> -#ifdef _GLIBCXX_SYSV_SEM
> - struct sembuf op[1] =
> - {
> - { 0, -1, SEM_UNDO }
> - };
> - if (semop(sem_set_, op, 1) == -1)
> - std::__throw_runtime_error("could not wait for semaphore");
> -#endif
> - }
> -
> // For use in 22_locale/time_get and time_put.
> std::tm
> test_tm(int sec, int min, int hour, int mday, int mon,
> diff --git a/libstdc++-v3/testsuite/util/testsuite_hooks.h
> b/libstdc++-v3/testsuite/util/testsuite_hooks.h
> index 49e8f0fe30bf..9d7bec18aa6f 100644
> --- a/libstdc++-v3/testsuite/util/testsuite_hooks.h
> +++ b/libstdc++-v3/testsuite/util/testsuite_hooks.h
> @@ -335,30 +335,6 @@ namespace __gnu_test
> }
> };
>
> - // A binary semaphore for use across multiple processes.
> - class semaphore
> - {
> - public:
> - // Creates a binary semaphore. The semaphore is initially in the
> - // unsignaled state.
> - semaphore();
> -
> - // Destroy the semaphore.
> - ~semaphore();
> -
> - // Signal the semaphore. If there are processes blocked in
> - // "wait", exactly one will be permitted to proceed.
> - void signal();
> -
> - // Wait until the semaphore is signaled.
> - void wait();
> -
> - private:
> - int sem_set_;
> -
> - pid_t pid_;
> - };
> -
> // For use in 22_locale/time_get and time_put.
> std::tm test_tm(int sec, int min, int hour, int mday, int mon,
> int year, int wday, int yday, int isdst);
> diff --git a/libstdc++-v3/testsuite/util/testsuite_semaphore.cc
> b/libstdc++-v3/testsuite/util/testsuite_semaphore.cc
> new file mode 100644
> index 000000000000..23bfba8af4cd
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/util/testsuite_semaphore.cc
> @@ -0,0 +1,153 @@
> +// -*- C++ -*-
> +
> +// Semaphore type for the C++ library testsuite.
> +//
> +// Copyright (C) 2005-2026 Free Software Foundation, Inc.
> +//
> +// This file is part of the GNU ISO C++ Library. This library is free
> +// software; you can redistribute it and/or modify it under the
> +// terms of the GNU General Public License as published by the
> +// Free Software Foundation; either version 3, or (at your option)
> +// any later version.
> +//
> +// This library is distributed in the hope that it will be useful,
> +// but WITHOUT ANY WARRANTY; without even the implied warranty of
> +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> +// GNU General Public License for more details.
> +//
> +// You should have received a copy of the GNU General Public License along
> +// with this library; see the file COPYING3. If not see
> +// <http://www.gnu.org/licenses/>.
> +//
> +
> +#include "testsuite_semaphore.h"
> +#include <bits/stdexcept_throw.h>
> +
> +#if defined(_GLIBCXX_HAVE_SYS_TYPES_H) \
> + && defined(_GLIBCXX_HAVE_SYS_IPC_H) \
> + && defined(_GLIBCXX_HAVE_SYS_SEM_H)
> +// If we have <sys/types.h>, <sys/ipc.h>, and <sys/sem.h>, then assume
> +// that System V semaphores are available.
> +# include <sys/types.h>
> +# include <sys/ipc.h>
> +# include <sys/sem.h>
> +# define _GLIBCXX_SYSV_SEM
> +#elif defined(_POSIX_SEMAPHORES) && _POSIX_SEMAPHORES > 0
> +# include <semaphore.h> // sem_init, sem_post etc.
> +# include <sys/mman.h> // mmap, MAP_SHARED etc.
> +# include <errno.h> // EINTR
> +# include <fcntl.h> // open, O_RDWR
> +# if !defined(MAP_ANONYMOUS) && defined(MAP_ANON)
> +# define MAP_ANONYMOUS MAP_ANON
> +# endif
> +# define _GLIBCXX_POSIX_SEM
> +#else
> +# include <stdlib.h> // abort
> +#endif
> +
> +namespace __gnu_test
> +{
> +#ifdef _GLIBCXX_SYSV_SEM
> + // This union is not declared in system headers. Instead, it must
> + // be defined by user programs.
> + union semun
> + {
> + int val = 0;
> + struct semid_ds *buf;
> + unsigned short *array;
> + };
> +
> + static void
> + destroy_semset(int set)
> + {
> + semctl(set, 0, IPC_RMID, semun{});
> + }
> +#endif
> +
> + semaphore::semaphore()
> + {
> +#ifdef _GLIBCXX_SYSV_SEM
> + // Get a semaphore set with one semaphore.
> + sem_set_ = semget(IPC_PRIVATE, 1, 0600);
> + if (sem_set_ == -1)
> + std::__throw_runtime_error("could not obtain semaphore set");
> +
> + // Initialize the semaphore.
> + if (semctl(sem_set_, 0, SETVAL, semun{}) == -1)
> + {
> + destroy_semset(sem_set_);
> + std::__throw_runtime_error("could not initialize semaphore");
> + }
> +#elif defined _GLIBCXX_POSIX_SEM
> +#ifdef MAP_ANONYMOUS
> + sem_ = mmap(nullptr, sizeof(sem_t), PROT_READ | PROT_WRITE,
> + MAP_SHARED | MAP_ANONYMOUS, -1, 0);
> +#else
> + int fd = open("/dev/zero", O_RDWR);
> + if (fd == -1)
> + std::__throw_runtime_error("could not open /dev/zero");
> + sem_ = mmap(nullptr, sizeof(sem_t), PROT_READ | PROT_WRITE,
> + MAP_SHARED, fd, 0);
> + close(fd);
> +#endif
> + if (sem_ == MAP_FAILED || sem_init((sem_t*)sem_, 1, 0))
I think we need to separate this two cases, and call munmap(sem_,
sizeof(sem_t)),
if mmap was successfull but sem_init failed.
> + std::__throw_runtime_error("could not create mmap'd semaphore");
> +#else
> + // There are no semaphores on this system. We have no way to mark
> + // a test as "unsupported" at runtime, so we just fail the test.
>
The comment above is no longer correct, as we have a way to mark a test as
unsupported.
// There are no semaphores on this system, so fail the test, to
signal that it
// should be marked as UNSUPPORTED.
> + // Use { dg-require-sysv-or-posix-semaphore "" } to make tests
> UNSUPPORTED.
> + abort();
> +#endif
> +
> + // Remember the PID for the process that created the semaphore
> + // so that only one process will destroy it.
> + pid_ = getpid();
> + }
> +
> + semaphore::~semaphore()
> + {
> + // Destroy the semaphore set only in the process that created it.
> +#ifdef _GLIBCXX_SYSV_SEM
> + if (pid_ == getpid())
> + destroy_semset(sem_set_);
> +#elif defined _GLIBCXX_POSIX_SEM
> + if (pid_ == getpid())
> + sem_destroy((sem_t*)sem_);
> + munmap(sem_, sizeof(sem_t));
> +#endif
> + }
> +
> + void
> + semaphore::signal()
> + {
> +#ifdef _GLIBCXX_SYSV_SEM
> + struct sembuf op[1] = { };
> + op[0].sem_op = 1;
> + if (semop(sem_set_, op, 1) == -1)
> + std::__throw_runtime_error("could not signal semaphore");
> +#elif defined _GLIBCXX_POSIX_SEM
> + if (sem_post((sem_t*)sem_))
> + std::__throw_runtime_error("could not signal semaphore");
> +#endif
> + }
> +
> + void
> + semaphore::wait()
> + {
> +#ifdef _GLIBCXX_SYSV_SEM
> + struct sembuf op[1] = { };
> + op[0].sem_op = -1;
> + op[0].sem_flg = SEM_UNDO;
> + if (semop(sem_set_, op, 1) == -1)
> + std::__throw_runtime_error("could not wait for semaphore");
> +#elif defined _GLIBCXX_POSIX_SEM
> + while (true)
> + {
> + if (sem_wait((sem_t*)sem_) == 0)
> + return;
> + if (errno != EINTR)
> + std::__throw_runtime_error("could not wait for semaphore");
> + }
> +#endif
> + }
> +} // namespace __gnu_test
> diff --git a/libstdc++-v3/testsuite/util/testsuite_semaphore.h
> b/libstdc++-v3/testsuite/util/testsuite_semaphore.h
> new file mode 100644
> index 000000000000..99e2e453668b
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/util/testsuite_semaphore.h
> @@ -0,0 +1,62 @@
> +// -*- C++ -*-
> +// Semaphore type for the C++ library testsuite.
> +//
> +// Copyright (C) 2005-2026 Free Software Foundation, Inc.
> +//
> +// This file is part of the GNU ISO C++ Library. This library is free
> +// software; you can redistribute it and/or modify it under the
> +// terms of the GNU General Public License as published by the
> +// Free Software Foundation; either version 3, or (at your option)
> +// any later version.
> +//
> +// This library is distributed in the hope that it will be useful,
> +// but WITHOUT ANY WARRANTY; without even the implied warranty of
> +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> +// GNU General Public License for more details.
> +//
> +// You should have received a copy of the GNU General Public License along
> +// with this library; see the file COPYING3. If not see
> +// <http://www.gnu.org/licenses/>.
> +//
> +
> +#ifndef _GLIBCXX_TESTSUITE_SEMAPHORE_H
> +#define _GLIBCXX_TESTSUITE_SEMAPHORE_H
> +
> +#include <bits/c++config.h>
> +
> +#ifdef _GLIBCXX_HAVE_UNISTD_H
> +# include <unistd.h>
> +#endif
> +
> +namespace __gnu_test
> +{
> + // A binary semaphore for use across multiple processes.
> + class semaphore
> + {
> + public:
> + // Creates a binary semaphore. The semaphore is initially in the
> + // unsignaled state.
> + semaphore();
> +
> + // Destroy the semaphore.
> + ~semaphore();
> +
> + // Signal the semaphore. If there are processes blocked in
> + // "wait", exactly one will be permitted to proceed.
> + void signal();
> +
> + // Wait until the semaphore is signaled.
> + void wait();
> +
> + private:
> + union {
> + int sem_set_;
> + void* sem_;
> + };
> + pid_t pid_;
> + };
> +
> +} // namespace __gnu_test
> +
> +#endif // _GLIBCXX_TESTSUITE_SEMAPHORE_H
> +
> --
> 2.55.0
>
>
