BLI: new basic CacheMutex

This patch introduces a new `CacheMutex` which makes it easy to implement
lazily computed caches in e.g. `Curves`. For more details see `BLI_cache_mutex.hh`.

Differential Revision: https://developer.blender.org/D16419

1 files changed, 25 insertions, 0 deletions

diff --git a/source/blender/blenlib/intern/cache_mutex.cc b/source/blender/blenlib/intern/cache_mutex.cc
new file mode 100644
index 00000000000..db474b1ef87
--- /dev/null
+++ b/source/blender/blenlib/intern/cache_mutex.cc
@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#include "BLI_cache_mutex.hh"
+#include "BLI_task.hh"
+
+namespace blender {
+
+void CacheMutex::ensure(const FunctionRef<void()> compute_cache)
+{
+  if (cache_valid_.load(std::memory_order_acquire)) {
+    return;
+  }
+  std::scoped_lock lock{mutex_};
+  /* Double checked lock. */
+  if (cache_valid_.load(std::memory_order_relaxed)) {
+    return;
+  }
+  /* Use task isolation because a mutex is locked and the cache computation might use
+   * multi-threading. */
+  threading::isolate_task(compute_cache);
+
+  cache_valid_.store(true, std::memory_order_release);
+}
+
+}  // namespace blender