From 778fbfa82d33ae21efdb48d2dc7bce08db51f140 Mon Sep 17 00:00:00 2001
From: Tom Rebbert <109624508+trebbert-lutron@users.noreply.github.com>
Date: Mon, 17 Oct 2022 19:57:50 -0600
Subject: [PATCH] [heap] move static heap construction to singleton accessor
 (#8242)

Move static heap construction to singleton accessor to avoid
non-trivial construction at global scope, which has an unpredictable
ordering.
---
 src/core/common/instance.cpp | 15 ++++++++++++++-
 src/core/common/instance.hpp |  4 ++--
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/src/core/common/instance.cpp b/src/core/common/instance.cpp
index c93a510f5..f066da81c 100644
--- a/src/core/common/instance.cpp
+++ b/src/core/common/instance.cpp
@@ -50,7 +50,8 @@ OT_DEFINE_ALIGNED_VAR(gInstanceRaw, sizeof(Instance), uint64_t);
 
 #if OPENTHREAD_MTD || OPENTHREAD_FTD
 #if !OPENTHREAD_CONFIG_HEAP_EXTERNAL_ENABLE
-Utils::Heap Instance::sHeap;
+OT_DEFINE_ALIGNED_VAR(sHeapRaw, sizeof(Utils::Heap), uint64_t);
+Utils::Heap *Instance::sHeap{nullptr};
 #endif
 #if OPENTHREAD_CONFIG_REFERENCE_DEVICE_ENABLE
 bool Instance::sDnsNameCompressionEnabled = true;
@@ -240,6 +241,18 @@ Instance::Instance(void)
 {
 }
 
+#if (OPENTHREAD_MTD || OPENTHREAD_FTD) && !OPENTHREAD_CONFIG_HEAP_EXTERNAL_ENABLE
+Utils::Heap &Instance::GetHeap(void)
+{
+    if (nullptr == sHeap)
+    {
+        sHeap = new (&sHeapRaw) Utils::Heap();
+    }
+
+    return *sHeap;
+}
+#endif
+
 #if !OPENTHREAD_CONFIG_MULTIPLE_INSTANCE_ENABLE
 
 Instance &Instance::InitSingle(void)
diff --git a/src/core/common/instance.hpp b/src/core/common/instance.hpp
index 78e6d45e9..f03e8bee5 100644
--- a/src/core/common/instance.hpp
+++ b/src/core/common/instance.hpp
@@ -290,7 +290,7 @@ public:
      * @returns A reference to the Heap object.
      *
      */
-    static Utils::Heap &GetHeap(void) { return sHeap; }
+    static Utils::Heap &GetHeap(void);
 #endif
 
 #if OPENTHREAD_CONFIG_COAP_API_ENABLE
@@ -381,7 +381,7 @@ private:
     // Random::Manager is initialized before other objects. Note that it
     // requires MbedTls which itself may use Heap.
 #if !OPENTHREAD_CONFIG_HEAP_EXTERNAL_ENABLE
-    static Utils::Heap sHeap;
+    static Utils::Heap *sHeap;
 #endif
     Crypto::MbedTls mMbedTls;
 #endif // OPENTHREAD_MTD || OPENTHREAD_FTD