CI: fix lint copyright + tsan races on PR #374

Three CI failures on feature/v2.0 PR #374 run 26183259463:

1. cpplint: examples/hello_world.cpp was missing the copyright line.
   Added single-line copyright header (the file is the deliberately
   minimal lambda-form example, so the full LGPL block would defeat
   its purpose).

2. tsan ws_start_stop: webserver::stop() and is_running() read
   impl_->running with no lock while start() writes it from the
   blocking-server thread. Made the field std::atomic<bool> — fixes
   the genuine race without changing the mutex/cond_var discipline
   that gates the blocking wait.

3. tsan route_table_concurrency + threadsafety_stress: libstdc++'s
   std::ctype<char>::narrow lazily fills a 256-byte cache; the guard
   flag is not atomic so concurrent std::regex compiles inside
   http_endpoint::http_endpoint look like a race even though every
   initialiser computes the same bytes. Added test/tsan.supp scoped
   to that one libstdc++ symbol pair, plumbed via TSAN_OPTIONS only
   on the tsan matrix lane, and shipped via test/Makefile.am
   EXTRA_DIST. Libhttpserver-internal races stay fatal.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: etr

.github/workflows/verify-build.yml

@@ -777,6 +777,11 @@ jobs:
     - name: Run tests
       run: |
         cd build ;
+        # tsan: suppress libstdc++'s benign std::ctype<char> narrow-cache race
+        # (see test/tsan.supp). All libhttpserver-internal races stay fatal.
+        if [ "$BUILD_TYPE" = "tsan" ]; then
+          export TSAN_OPTIONS="suppressions=$(pwd)/../test/tsan.supp" ;
+        fi
         make check;
       # TASK-037: flag-invariance-{on,off} are compile/link-only gates, so
       # skip the full `make check` (which spins up real servers and would

examples/hello_world.cpp

@@ -1,3 +1,4 @@
+// Copyright 2026 Sebastiano Merlino
 // libhttpserver hello-world example — the lambda form (PRD §3.4).
 // Compiles in ten lines including main(), with no http_resource subclass
 // and no raw-pointer ownership. Production code typically qualifies names

src/httpserver/detail/webserver_impl.hpp

@@ -42,6 +42,7 @@
 #include <stdarg.h>
 
 #include <array>
+#include <atomic>
 #include <cstddef>
 #include <cstring>
 #include <list>
@@ -183,7 +184,10 @@ class webserver_impl {
     pthread_mutex_t mutexwait;
     pthread_cond_t  mutexcond;
 
-    bool running = false;
+    // Atomic to allow lock-free reads in stop()/is_running() concurrent
+    // with the mutex-guarded writes in start()/stop(). TSan-flagged in the
+    // ws_start_stop integ test (start on worker thread, stop on main).
+    std::atomic<bool> running{false};
 
     // TASK-023: route-table entries hold shared_ptr<http_resource>.
     // The two public register_resource overloads (unique_ptr / shared_ptr)

test/Makefile.am

@@ -344,6 +344,7 @@ TESTS = $(check_PROGRAMS)
 @VALGRIND_CHECK_RULES@
 VALGRIND_SUPPRESSIONS_FILES = libhttpserver.supp
 EXTRA_DIST = libhttpserver.supp \
+             tsan.supp \
              PERFORMANCE.md \
              v1_baseline/README.md \
              v1_baseline/v1_constants.hpp \

test/tsan.supp

@@ -0,0 +1,14 @@
+# ThreadSanitizer suppressions for libhttpserver tests.
+#
+# Each entry below is a documented libstdc++ benign race; suppress at the
+# library boundary only — never inside libhttpserver code. New races in
+# libhttpserver itself MUST be fixed, not suppressed.
+
+# libstdc++ lazily fills std::ctype<char>::_M_narrow_ok / _M_narrow on the
+# first call to narrow() (commonly the first std::regex compile). The cache
+# write is idempotent — every initialiser computes the same 256-byte table —
+# but the guard flag is not declared atomic, so TSan flags concurrent writers
+# even though the resulting state is identical. Reported as a libstdc++ bug
+# upstream (gcc bug #58938 and related); benign in practice.
+race:std::ctype<char>::narrow
+race:std::ctype<char>::_M_narrow_init