[gcc r16-1271] libstdc++: Add more tests for semaphores

[Jonathan Wakely via Libstdc++-cvs]

https://gcc.gnu.org/g:37fe7e7069c2bb999c95a9807a8f895f38b9cacf

commit r16-1271-g37fe7e7069c2bb999c95a9807a8f895f38b9cacf
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Fri Jun 6 17:18:40 2025 +0100

    libstdc++: Add more tests for semaphores
    
    libstdc++-v3/ChangeLog:
    
            * testsuite/30_threads/semaphore/1.cc: Check type properties and
            max() values.
            * testsuite/30_threads/semaphore/3.cc: New test.
            * testsuite/30_threads/semaphore/cons_neg.cc: New test.

Diff:
---
 libstdc++-v3/testsuite/30_threads/semaphore/1.cc   | 22 ++++++++++++++++++++++
 libstdc++-v3/testsuite/30_threads/semaphore/3.cc   | 19 +++++++++++++++++++
 .../testsuite/30_threads/semaphore/cons_neg.cc     | 12 ++++++++++++
 3 files changed, 53 insertions(+)

diff --git a/libstdc++-v3/testsuite/30_threads/semaphore/1.cc 
b/libstdc++-v3/testsuite/30_threads/semaphore/1.cc
index cc6befcc1a50..9472def4cba1 100644
--- a/libstdc++-v3/testsuite/30_threads/semaphore/1.cc
+++ b/libstdc++-v3/testsuite/30_threads/semaphore/1.cc
@@ -27,3 +27,25 @@
 #elif __cpp_lib_semaphore != 201907L
 # error "Feature-test macro for semaphore has wrong value in <semaphore>"
 #endif
+
+static_assert(std::is_same_v<std::counting_semaphore<1>,
+                            std::binary_semaphore>);
+
+static_assert(! std::is_same_v<std::counting_semaphore<2>,
+                              std::binary_semaphore>);
+
+static_assert(! std::is_same_v<std::counting_semaphore<>,
+                              std::binary_semaphore>);
+
+// The standard permits max() to be greater than the template argument,
+// but for the current libstdc++ implementation it's always equal to it.
+static_assert(std::binary_semaphore::max() == 1);
+static_assert(std::counting_semaphore<0>::max() == 0);
+static_assert(std::counting_semaphore<2>::max() == 2);
+
+#include <limits.h>
+
+static_assert(std::counting_semaphore<INT_MAX>::max() == INT_MAX);
+static_assert(std::counting_semaphore<INT_MAX-1>::max() == INT_MAX-1);
+static_assert(std::counting_semaphore<PTRDIFF_MAX>::max() == PTRDIFF_MAX);
+static_assert(std::counting_semaphore<PTRDIFF_MAX-3>::max() == PTRDIFF_MAX-3);
diff --git a/libstdc++-v3/testsuite/30_threads/semaphore/3.cc 
b/libstdc++-v3/testsuite/30_threads/semaphore/3.cc
new file mode 100644
index 000000000000..51b9fbb0e4bd
--- /dev/null
+++ b/libstdc++-v3/testsuite/30_threads/semaphore/3.cc
@@ -0,0 +1,19 @@
+// { dg-do compile { target *-*-*linux* } }
+// { dg-require-effective-target c++20 }
+// { dg-require-effective-target hosted }
+
+#include <semaphore>
+#include <limits.h>
+
+// on Linux these specializations all use a futex:
+static_assert(sizeof(std::counting_semaphore<0>) == sizeof(int));
+static_assert(sizeof(std::counting_semaphore<1>) == sizeof(int));
+static_assert(sizeof(std::counting_semaphore<INT_MAX>) == sizeof(int));
+static_assert(sizeof(std::counting_semaphore<>) == sizeof(int));
+
+// This will use a futex iff ptrdiff_t has 32 bits:
+static_assert(sizeof(std::counting_semaphore<PTRDIFF_MAX>) == 
sizeof(std::ptrdiff_t));
+
+#if PTRDIFF_MAX > INT_MAX
+static_assert(sizeof(std::counting_semaphore<INT_MAX+1LL>) == 
sizeof(std::ptrdiff_t));
+#endif
diff --git a/libstdc++-v3/testsuite/30_threads/semaphore/cons_neg.cc 
b/libstdc++-v3/testsuite/30_threads/semaphore/cons_neg.cc
new file mode 100644
index 000000000000..56e27d7ddc4c
--- /dev/null
+++ b/libstdc++-v3/testsuite/30_threads/semaphore/cons_neg.cc
@@ -0,0 +1,12 @@
+// { dg-options "-D_GLIBCXX_ASSERTIONS" }
+// { dg-do run { target c++20 xfail *-*-* } }
+// { dg-require-effective-target hosted }
+// { dg-add-options libatomic }
+
+#include <semaphore>
+
+int main()
+{
+  // Preconditions: desired >= 0 is true, and desired <= max() is true.
+  std::binary_semaphore b(2);
+}