fix(profiling): guard against invalid access on exit

Co-authored-by: KowalskiThomas <14239160+KowalskiThomas@users.noreply.github.com>

Author: datadog-datadog-prod-us1-2[bot]

ddtrace/internal/datadog/profiling/stack/include/sampler.hpp

@@ -38,6 +38,7 @@ class Sampler
 
     // This is a singleton, so no public constructor
     Sampler();
+    ~Sampler();
 
     // One-time setup of echion
     void one_time_setup();

ddtrace/internal/datadog/profiling/stack/src/sampler.cpp

@@ -258,6 +258,18 @@ Sampler::Sampler()
 {
 }
 
+Sampler::~Sampler()
+{
+    stop();
+    if (thread_running.load()) {
+        // The sampling thread is still alive after the timeout in stop().
+        // Leak the EchionSampler so the thread does not access destroyed
+        // data structures (StringTable, FrameCache, etc.) — this prevents
+        // a SIGSEGV in the hash-table code during process exit.
+        (void)echion.release();
+    }
+}
+
 Sampler&
 Sampler::get()
 {

releasenotes/notes/profiling-fix-segv-sampling-thread-exit-e909f07be050246c.yaml

@@ -0,0 +1,9 @@
+---
+fixes:
+  - |
+    profiling: This fix resolves a SIGSEGV crash (in ``StringTable::key``) that occurred when the
+    profiling sampling thread was still running during process exit. The Sampler singleton's
+    default destructor destroyed the ``EchionSampler`` (and its hash tables) while the detached
+    sampling thread was still accessing them. The fix adds an explicit destructor that calls
+    ``stop()`` and, if the thread does not exit in time, leaks the ``EchionSampler`` to prevent
+    use-after-free.