Make sure Scheduler::GetCurrent() cannot return a nullptr (#2887)

include/mbgl/actor/scheduler.hpp

@@ -80,7 +80,8 @@ public:
     virtual void waitForEmpty(const util::SimpleIdentity = util::SimpleIdentity::Empty) = 0;
 
     /// Set/Get the current Scheduler for this thread
-    static Scheduler* GetCurrent();
+    /// @param init initialize if missing
+    static Scheduler* GetCurrent(bool init = true);
     static void SetCurrent(Scheduler*);
 
     /// Get the scheduler for asynchronous tasks. This method

platform/android/MapLibreAndroid/src/cpp/jni_native.cpp

@@ -68,8 +68,6 @@ void registerNatives(JavaVM* vm) {
 
     jni::JNIEnv& env = jni::GetEnv(*vm, jni::jni_version_1_6);
 
-    // For the FileSource
-    static mbgl::util::RunLoop mainRunLoop;
     FileSource::registerNative(env);
 
     // Basic types

platform/darwin/src/run_loop.cpp

@@ -21,7 +21,7 @@ RunLoop* RunLoop::Get() {
 
 RunLoop::RunLoop(Type)
     : impl(std::make_unique<Impl>()) {
-    assert(!Scheduler::GetCurrent());
+    assert(!Scheduler::GetCurrent(false));
     Scheduler::SetCurrent(this);
     impl->async = std::make_unique<AsyncTask>(std::bind(&RunLoop::process, this));
 }

platform/windows/windows.cmake

@@ -266,6 +266,12 @@ target_link_libraries(
         $<IF:$<TARGET_EXISTS:libuv::uv_a>,libuv::uv_a,libuv::uv>
 )
 
+target_link_libraries(
+    mbgl-expression-test
+    PRIVATE
+        $<IF:$<TARGET_EXISTS:libuv::uv_a>,libuv::uv_a,libuv::uv>
+)
+
 # Disable benchmarks in CI as they run in VM environment
 if(NOT DEFINED ENV{CI})
     add_test(NAME mbgl-benchmark-runner COMMAND mbgl-benchmark-runner WORKING_DIRECTORY ${PROJECT_SOURCE_DIR})

src/mbgl/actor/scheduler.cpp

@@ -1,6 +1,7 @@
 #include <mbgl/actor/scheduler.hpp>
 #include <mbgl/util/thread_local.hpp>
 #include <mbgl/util/thread_pool.hpp>
+#include <mbgl/util/run_loop.hpp>
 
 namespace mbgl {
 
@@ -22,7 +23,11 @@ void Scheduler::SetCurrent(Scheduler* scheduler) {
     localScheduler = scheduler;
 }
 
-Scheduler* Scheduler::GetCurrent() {
+Scheduler* Scheduler::GetCurrent(bool init) {
+    if (!localScheduler && init) {
+        thread_local util::RunLoop runLoop;
+        SetCurrent(&runLoop);
+    }
     return localScheduler;
 }