lib/Twig/lib/Twig/Environment.php
public function addGlobal($name, $value)
    {
        if ($this->extensionInitialized || $this->runtimeInitialized) {
            if (null === $this->globals) {
                $this->globals = $this->initGlobals();
            }

            if (!array_key_exists($name, $this->globals)) {
                // The deprecation notice must be turned into the following exception in Twig 2.0
                @trigger_error(sprintf('Registering global variable "%s" at runtime or when the extensions have already been initialized is deprecated since version 1.21.', $name), E_USER_DEPRECATED);
                //throw new LogicException(sprintf('Unable to add global "%s" as the runtime or the extensions have already been initialized.', $name));
            }
        }

        if ($this->extensionInitialized || $this->runtimeInitialized) {
            // update the value
            $this->globals[$name] = $value;
        } else {
            $this->staging->addGlobal($name, $value);
        }
    }
public function addGlobal($name, $value)
    {
        if ($this->extensionInitialized || $this->runtimeInitialized) {
            if (null === $this->globals) {
                $this->globals = $this->initGlobals();
            }

            if (!array_key_exists($name, $this->globals)) {
                // The deprecation notice must be turned into the following exception in Twig 2.0
                @trigger_error(sprintf('Registering global variable "%s" at runtime or when the extensions have already been initialized is deprecated since version 1.21.', $name), E_USER_DEPRECATED);
                //throw new LogicException(sprintf('Unable to add global "%s" as the runtime or the extensions have already been initialized.', $name));
            }
        }

        if ($this->extensionInitialized || $this->runtimeInitialized) {
            // update the value
            $this->globals[$name] = $value;
        } else {
            $this->staging->addGlobal($name, $value);
        }
    }
Registers a Global.

New globals can be added before compiling or rendering a template;
but after, you can only update existing globals.

@param string $name  The global name
@param mixed  $value The global value