Allow the thread limit to be set globally via an environment variable.

docs/source/tutorials/misc.rst

@@ -118,6 +118,14 @@ However, with multi-threading enabled, it is expected that the results can be no
 
         to reset the number of threads to the default.
 
+        The thread limit can also be controlled by setting the ``TBB_NUM_THREADS`` environment variable before importing ``ipctk``. This is useful in production environments where you want to enforce a global thread limit without modifying every script that uses the IPC Toolkit:
+
+        .. code-block:: bash
+
+            export TBB_NUM_THREADS=1
+
+        If set, this takes effect as soon as ``ipctk`` is imported (equivalent to calling ``ipctk.set_num_threads`` with the given value), and can still be overridden later in the script by calling ``ipctk.set_num_threads`` directly. If the variable is unset or invalid, it is ignored and the default thread count is used.
+
 You can also get the current maximum number of threads as follows:
 
 .. md-tab-set::

python/src/utils/thread_limiter.cpp

@@ -41,5 +41,17 @@ void define_thread_limiter(py::module_& m)
         "set_num_threads", &set_num_threads,
         "set maximum number of threads to use", "nthreads"_a);
 
+    // Allow the thread limit to be set globally via an environment variable
+    // (e.g., in production) rather than requiring every script to call
+    // set_num_threads() itself.
+    const char* env_val = std::getenv("TBB_NUM_THREADS");
+    if (env_val != nullptr) {
+        try {
+            set_num_threads(std::stoi(env_val));
+        } catch (const std::exception& e) {
+            logger().error("Invalid value for TBB_NUM_THREADS: {}", env_val);
+        }
+    }
+
     std::atexit([]() { thread_limiter.reset(); });
 }