adding a tryGetAllocator

Author: kab163

docs/sphinx/tutorial/resources.rst

@@ -35,6 +35,21 @@ example:
    :end-before: _sphinx_tag_tut_get_allocator_end
    :language: C++
 
+If you would prefer to avoid exceptions when an allocator is not available,
+you can instead use :func:`umpire::ResourceManager::tryGetAllocator`, which
+returns a ``std::optional<umpire::Allocator>`` that is empty when the
+requested allocator cannot be found:
+
+.. code-block:: cpp
+
+  auto& rm = umpire::ResourceManager::getInstance();
+  auto maybe_allocator = rm.tryGetAllocator("HOST");
+
+  if (maybe_allocator) {
+    auto allocator = *maybe_allocator;
+    // use allocator
+  }
+
 Note that since every allocator supports the same calls, no matter which resource 
 it is for, this means we can run the same code for all the resources available in
 the system.

src/umpire/ResourceManager.cpp

@@ -209,6 +209,29 @@ strategy::AllocationStrategy* ResourceManager::getAllocationStrategy(const std::
   return m_allocators_by_name[name];
 }
 
+std::optional<Allocator> ResourceManager::tryGetAllocator(const std::string& name)
+{
+  UMPIRE_LOG(Debug, "(\"" << name << "\")");
+
+  resource::MemoryResourceRegistry& registry{resource::MemoryResourceRegistry::getInstance()};
+  auto resource_names = registry.getResourceNames();
+
+  auto allocator = m_allocators_by_name.find(name);
+  if (allocator == m_allocators_by_name.end()) {
+    auto resource_name = std::find(resource_names.begin(), resource_names.end(), name);
+    if (resource_name != std::end(resource_names)) {
+      makeResource(name);
+      allocator = m_allocators_by_name.find(name);
+    }
+  }
+
+  if (allocator == m_allocators_by_name.end()) {
+    return std::nullopt;
+  }
+
+  return Allocator{allocator->second};
+}
+
 Allocator ResourceManager::getAllocator(const std::string& name)
 {
   UMPIRE_LOG(Debug, "(\"" << name << "\")");

src/umpire/ResourceManager.hpp

@@ -10,6 +10,7 @@
 #include <list>
 #include <memory>
 #include <mutex>
+#include <optional>
 #include <string>
 #include <unordered_map>
 #include <vector>
@@ -67,6 +68,14 @@ class ResourceManager {
    */
   Allocator getAllocator(const std::string& name);
 
+  /*!
+   * \brief Try to get the Allocator with the given name.
+   *
+   * This function returns an empty optional if the allocator does not exist
+   * or cannot be created, instead of throwing an exception.
+   */
+  std::optional<Allocator> tryGetAllocator(const std::string& name);
+
   Allocator getAllocator(const char* name);
 
   /*!

tests/integration/allocator_integration_tests.cpp

@@ -230,6 +230,18 @@ TEST(Allocator, registerAllocator)
   ASSERT_FALSE(rm.isAllocator("BANANAS"));
 }
 
+TEST(Allocator, TryGetAllocator)
+{
+  auto& rm = umpire::ResourceManager::getInstance();
+
+  auto host_allocator = rm.tryGetAllocator("HOST");
+  ASSERT_TRUE(host_allocator.has_value());
+  EXPECT_EQ(std::string{"HOST"}, host_allocator->getName());
+
+  auto bad_allocator = rm.tryGetAllocator("BANANAS");
+  EXPECT_FALSE(bad_allocator.has_value());
+}
+
 TEST(Allocator, GetSetDefault)
 {
   auto& rm = umpire::ResourceManager::getInstance();