diff --git a/CMakeLists.txt b/CMakeLists.txt
index 37789cc..0589d0d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1549,6 +1549,25 @@
     target_link_libraries(llvm dl)
 endif()
 
+
+###########################################################
+# marl
+###########################################################
+if(BUILD_MARL)
+    set(MARL_THIRD_PARTY_DIR ${THIRD_PARTY_DIR})
+    add_subdirectory(third_party/marl)
+endif()
+
+
+###########################################################
+# cppdap
+###########################################################
+if(SWIFTSHADER_BUILD_CPPDAP)
+    set(CPPDAP_THIRD_PARTY_DIR ${THIRD_PARTY_DIR})
+    add_subdirectory(${CPPDAP_DIR})
+endif()
+
+
 ###########################################################
 # Subzero
 ###########################################################
@@ -1696,6 +1715,8 @@
     )
     target_link_libraries(ReactorSubzero SubzeroDependencies)
 
+    target_link_libraries(ReactorSubzero marl)
+
     if(WIN32)
         target_compile_definitions(ReactorSubzero PRIVATE SUBZERO_USE_MICROSOFT_ABI)
     endif()
@@ -2157,16 +2178,6 @@
     )
 endif(SWIFTSHADER_BUILD_GLES_CM)
 
-if(BUILD_MARL)
-    set(MARL_THIRD_PARTY_DIR ${THIRD_PARTY_DIR})
-    add_subdirectory(third_party/marl)
-endif()
-
-if(SWIFTSHADER_BUILD_CPPDAP)
-    set(CPPDAP_THIRD_PARTY_DIR ${THIRD_PARTY_DIR})
-    add_subdirectory(${CPPDAP_DIR})
-endif()
-
 if(SWIFTSHADER_BUILD_VULKAN)
     add_library(vk_swiftshader SHARED ${VULKAN_LIST})
 
@@ -2322,9 +2333,9 @@
     )
 
     if(NOT WIN32 AND ${REACTOR_BACKEND} STREQUAL "Subzero")
-        target_link_libraries(ReactorUnitTests ${Reactor} pthread dl)
+        target_link_libraries(ReactorUnitTests ${Reactor} marl pthread dl)
     else()
-        target_link_libraries(ReactorUnitTests ${Reactor})
+        target_link_libraries(ReactorUnitTests ${Reactor} marl)
     endif()
 
     set(GLES_UNITTESTS_LIST
@@ -2390,7 +2401,7 @@
     )
 
     add_executable(ReactorBenchmarks ${REACTOR_BENCHMARK_LIST})
-    target_link_libraries(ReactorBenchmarks benchmark::benchmark ${Reactor})
+    target_link_libraries(ReactorBenchmarks benchmark::benchmark marl ${Reactor})
 
     set_target_properties(ReactorBenchmarks PROPERTIES
         COMPILE_OPTIONS "${SWIFTSHADER_COMPILE_OPTIONS};${WARNINGS_AS_ERRORS}"
diff --git a/src/Reactor/ReactorUnitTests.cpp b/src/Reactor/ReactorUnitTests.cpp
index bcfd13d..7e38d93 100644
--- a/src/Reactor/ReactorUnitTests.cpp
+++ b/src/Reactor/ReactorUnitTests.cpp
@@ -18,6 +18,9 @@
 
 #include "gtest/gtest.h"
 
+#include "marl/defer.h"
+#include "marl/scheduler.h"
+
 #include <array>
 #include <cmath>
 #include <thread>
@@ -155,6 +158,38 @@
 	return result;
 }
 
+static const std::vector<int> fibonacci = {
+	0,
+	1,
+	1,
+	2,
+	3,
+	5,
+	8,
+	13,
+	21,
+	34,
+	55,
+	89,
+	144,
+	233,
+	377,
+	610,
+	987,
+	1597,
+	2584,
+	4181,
+	6765,
+	10946,
+	17711,
+	28657,
+	46368,
+	75025,
+	121393,
+	196418,
+	317811,
+};
+
 TEST(ReactorUnitTests, PrintPrimitiveTypes)
 {
 #if defined(ENABLE_RR_PRINT) && !defined(ENABLE_RR_EMIT_PRINT_LOCATION)
@@ -2070,6 +2105,30 @@
 	}
 }
 
+TEST(ReactorUnitTests, Fibonacci)
+{
+	FunctionT<int(int)> function;
+	{
+		Int n = function.Arg<0>();
+		Int current = 0;
+		Int next = 1;
+		For(Int i = 0, i < n, i++)
+		{
+			auto tmp = current + next;
+			current = next;
+			next = tmp;
+		}
+		Return(current);
+	}
+
+	auto routine = function("one");
+
+	for(size_t i = 0; i < fibonacci.size(); i++)
+	{
+		EXPECT_EQ(routine(i), fibonacci[i]);
+	}
+}
+
 TEST(ReactorUnitTests, Coroutines_Fibonacci)
 {
 	if(!rr::Caps.CoroutinesSupported)
@@ -2078,6 +2137,11 @@
 		return;
 	}
 
+	marl::Scheduler scheduler;
+	scheduler.setWorkerThreadCount(8);
+	scheduler.bind();
+	defer(scheduler.unbind());
+
 	Coroutine<int()> function;
 	{
 		Yield(Int(0));
@@ -2095,45 +2159,11 @@
 
 	auto coroutine = function();
 
-	int32_t expected[] = {
-		0,
-		1,
-		1,
-		2,
-		3,
-		5,
-		8,
-		13,
-		21,
-		34,
-		55,
-		89,
-		144,
-		233,
-		377,
-		610,
-		987,
-		1597,
-		2584,
-		4181,
-		6765,
-		10946,
-		17711,
-		28657,
-		46368,
-		75025,
-		121393,
-		196418,
-		317811,
-	};
-
-	auto count = sizeof(expected) / sizeof(expected[0]);
-
-	for(size_t i = 0; i < count; i++)
+	for(size_t i = 0; i < fibonacci.size(); i++)
 	{
 		int out = 0;
 		EXPECT_EQ(coroutine->await(out), true);
-		EXPECT_EQ(out, expected[i]);
+		EXPECT_EQ(out, fibonacci[i]);
 	}
 }
 
@@ -2145,6 +2175,11 @@
 		return;
 	}
 
+	marl::Scheduler scheduler;
+	scheduler.setWorkerThreadCount(8);
+	scheduler.bind();
+	defer(scheduler.unbind());
+
 	Coroutine<uint8_t(uint8_t * data, int count)> function;
 	{
 		Pointer<Byte> data = function.Arg<0>();
@@ -2186,6 +2221,11 @@
 		return;
 	}
 
+	marl::Scheduler scheduler;
+	scheduler.setWorkerThreadCount(8);
+	scheduler.bind();
+	defer(scheduler.unbind());
+
 	Coroutine<int()> function;
 	{
 		Int4 a{ 1, 2, 3, 4 };
@@ -2220,6 +2260,11 @@
 		return;
 	}
 
+	marl::Scheduler scheduler;
+	scheduler.setWorkerThreadCount(8);
+	scheduler.bind();
+	defer(scheduler.unbind());
+
 	for(int i = 0; i < 2; ++i)
 	{
 		Coroutine<int()> function;
@@ -2244,6 +2289,11 @@
 		return;
 	}
 
+	marl::Scheduler scheduler;
+	scheduler.setWorkerThreadCount(8);
+	//scheduler.bind();
+	//defer(scheduler.unbind());
+
 	Coroutine<int()> function;
 	{
 		Yield(Int(0));
@@ -2262,53 +2312,22 @@
 	// Must call on same thread that creates the coroutine
 	function.finalize();
 
-	constexpr int32_t expected[] = {
-		0,
-		1,
-		1,
-		2,
-		3,
-		5,
-		8,
-		13,
-		21,
-		34,
-		55,
-		89,
-		144,
-		233,
-		377,
-		610,
-		987,
-		1597,
-		2584,
-		4181,
-		6765,
-		10946,
-		17711,
-		28657,
-		46368,
-		75025,
-		121393,
-		196418,
-		317811,
-	};
-
-	constexpr auto count = sizeof(expected) / sizeof(expected[0]);
-
 	std::vector<std::thread> threads;
 	const size_t numThreads = 100;
 
 	for(size_t t = 0; t < numThreads; ++t)
 	{
 		threads.emplace_back([&] {
+			scheduler.bind();
+			defer(scheduler.unbind());
+
 			auto coroutine = function();
 
-			for(size_t i = 0; i < count; i++)
+			for(size_t i = 0; i < fibonacci.size(); i++)
 			{
 				int out = 0;
 				EXPECT_EQ(coroutine->await(out), true);
-				EXPECT_EQ(out, expected[i]);
+				EXPECT_EQ(out, fibonacci[i]);
 			}
 		});
 	}
diff --git a/src/Reactor/SubzeroReactor.cpp b/src/Reactor/SubzeroReactor.cpp
index 6602ddd..df12cb1 100644
--- a/src/Reactor/SubzeroReactor.cpp
+++ b/src/Reactor/SubzeroReactor.cpp
@@ -33,6 +33,8 @@
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/raw_os_ostream.h"
 
+#include "marl/event.h"
+
 #if __has_feature(memory_sanitizer)
 #	include <sanitizer/msan_interface.h>
 #endif
@@ -380,11 +382,7 @@
 }
 
 const Capabilities Caps = {
-#if defined(_WIN32)
 	true,  // CoroutinesSupported
-#else
-	false,  // CoroutinesSupported
-#endif
 };
 
 enum EmulatedType
@@ -4464,19 +4462,15 @@
 namespace {
 namespace coro {
 
-using FiberHandle = void *;
-
 // Instance data per generated coroutine
 // This is the "handle" type used for Coroutine functions
 // Lifetime: from yield to when CoroutineEntryDestroy generated function is called.
 struct CoroutineData
 {
-	FiberHandle mainFiber{};
-	FiberHandle routineFiber{};
-	bool convertedFiber = false;
-
-	// Variables used by coroutines
-	bool done = false;
+	marl::Event suspended;                                // the coroutine is suspended on a yield()
+	marl::Event resumed;                                  // the caller is suspended on an await()
+	marl::Event done{ marl::Event::Mode::Manual };        // the coroutine should stop at the next yield()
+	marl::Event terminated{ marl::Event::Mode::Manual };  // the coroutine has finished.
 	void *promisePtr = nullptr;
 };
 
@@ -4490,108 +4484,36 @@
 	delete coroData;
 }
 
-void convertThreadToMainFiber(Nucleus::CoroutineHandle handle)
+// suspend() pauses execution of the coroutine, and resumes execution from the
+// caller's call to await().
+// Returns true if await() is called again, or false if coroutine_destroy()
+// is called.
+bool suspend(Nucleus::CoroutineHandle handle)
 {
-#if defined(_WIN32)
-	auto *coroData = reinterpret_cast<CoroutineData *>(handle);
-
-	coroData->mainFiber = ::ConvertThreadToFiber(nullptr);
-
-	if(coroData->mainFiber)
-	{
-		coroData->convertedFiber = true;
-	}
-	else
-	{
-		// We're probably already on a fiber, so just grab it and remember that we didn't
-		// convert it, so not to convert back to thread.
-		coroData->mainFiber = GetCurrentFiber();
-		coroData->convertedFiber = false;
-	}
-	ASSERT(coroData->mainFiber);
-#else
-	UNIMPLEMENTED_NO_BUG("convertThreadToMainFiber not implemented for current platform");
-#endif
+	auto *data = reinterpret_cast<CoroutineData *>(handle);
+	data->suspended.signal();
+	data->resumed.wait();
+	return !data->done.test();
 }
 
-void convertMainFiberToThread(Nucleus::CoroutineHandle handle)
+// resume() is called by await(), blocking until the coroutine calls yield()
+// or the coroutine terminates.
+void resume(Nucleus::CoroutineHandle handle)
 {
-#if defined(_WIN32)
-	auto *coroData = reinterpret_cast<CoroutineData *>(handle);
-
-	ASSERT(coroData->mainFiber);
-
-	if(coroData->convertedFiber)
-	{
-		::ConvertFiberToThread();
-		coroData->mainFiber = nullptr;
-	}
-#else
-	UNIMPLEMENTED_NO_BUG("convertMainFiberToThread not implemented for current platform");
-#endif
-}
-using FiberFunc = std::function<void()>;
-
-void createRoutineFiber(Nucleus::CoroutineHandle handle, FiberFunc *fiberFunc)
-{
-#if defined(_WIN32)
-	struct Invoker
-	{
-		FiberFunc func;
-
-		static VOID __stdcall fiberEntry(LPVOID lpParameter)
-		{
-			auto *func = reinterpret_cast<FiberFunc *>(lpParameter);
-			(*func)();
-		}
-	};
-
-	auto *coroData = reinterpret_cast<CoroutineData *>(handle);
-
-	constexpr SIZE_T StackSize = 2 * 1024 * 1024;
-	coroData->routineFiber = ::CreateFiber(StackSize, &Invoker::fiberEntry, fiberFunc);
-	ASSERT(coroData->routineFiber);
-#else
-	UNIMPLEMENTED_NO_BUG("createRoutineFiber not implemented for current platform");
-#endif
+	auto *data = reinterpret_cast<CoroutineData *>(handle);
+	data->resumed.signal();
+	data->suspended.wait();
 }
 
-void deleteRoutineFiber(Nucleus::CoroutineHandle handle)
+// stop() is called by coroutine_destroy(), signalling that it's done, then blocks
+// until the coroutine ends, and deletes the coroutine data.
+void stop(Nucleus::CoroutineHandle handle)
 {
-#if defined(_WIN32)
 	auto *coroData = reinterpret_cast<CoroutineData *>(handle);
-	ASSERT(coroData->routineFiber);
-	::DeleteFiber(coroData->routineFiber);
-	coroData->routineFiber = nullptr;
-#else
-	UNIMPLEMENTED_NO_BUG("deleteRoutineFiber not implemented for current platform");
-#endif
-}
-
-void switchToMainFiber(Nucleus::CoroutineHandle handle)
-{
-#if defined(_WIN32)
-	auto *coroData = reinterpret_cast<CoroutineData *>(handle);
-
-	// Win32
-	ASSERT(coroData->mainFiber);
-	::SwitchToFiber(coroData->mainFiber);
-#else
-	UNIMPLEMENTED_NO_BUG("switchToMainFiber not implemented for current platform");
-#endif
-}
-
-void switchToRoutineFiber(Nucleus::CoroutineHandle handle)
-{
-#if defined(_WIN32)
-	auto *coroData = reinterpret_cast<CoroutineData *>(handle);
-
-	// Win32
-	ASSERT(coroData->routineFiber);
-	::SwitchToFiber(coroData->routineFiber);
-#else
-	UNIMPLEMENTED_NO_BUG("switchToRoutineFiber not implemented for current platform");
-#endif
+	coroData->done.signal();               // signal that the coroutine should stop at next (or current) yield.
+	coroData->resumed.signal();            // wake the coroutine if blocked on a yield.
+	coroData->terminated.wait();           // wait for the coroutine to return.
+	coro::destroyCoroutineData(coroData);  // free the coroutine data.
 }
 
 namespace detail {
@@ -4612,17 +4534,10 @@
 	return handle;
 }
 
-void setDone(Nucleus::CoroutineHandle handle)
-{
-	auto *coroData = reinterpret_cast<CoroutineData *>(handle);
-	ASSERT(!coroData->done);  // Should be called once
-	coroData->done = true;
-}
-
 bool isDone(Nucleus::CoroutineHandle handle)
 {
 	auto *coroData = reinterpret_cast<CoroutineData *>(handle);
-	return coroData->done;
+	return coroData->done.test();
 }
 
 void setPromisePtr(Nucleus::CoroutineHandle handle, void *promisePtr)
@@ -4697,30 +4612,27 @@
 		//        ... <REACTOR CODE> ...
 		//
 		//        promise = val;
-		//        coro::switchToMainFiber(handle);
+		//        if (!coro::suspend(handle)) {
+		//            return false; // coroutine has been stopped by the caller.
+		//        }
 		//
 		//        ... <REACTOR CODE> ...
 
+		//        promise = val;
 		Nucleus::createStore(val, V(this->promise), ::coroYieldType);
-		sz::Call(::function, ::basicBlock, coro::switchToMainFiber, this->handle);
-	}
 
-	// Adds instructions at the end of the current main coroutine function to end the coroutine.
-	void generateCoroutineEnd()
-	{
+		//        if (!coro::suspend(handle)) {
+		auto result = sz::Call(::function, ::basicBlock, coro::suspend, this->handle);
+		auto doneBlock = Nucleus::createBasicBlock();
+		auto resumeBlock = Nucleus::createBasicBlock();
+		Nucleus::createCondBr(V(result), resumeBlock, doneBlock);
+
+		//            return false; // coroutine has been stopped by the caller.
+		::basicBlock = doneBlock;
+		Nucleus::createRetVoid();  // coroutine return value is ignored.
+
 		//        ... <REACTOR CODE> ...
-		//
-		//        coro::setDone(handle);
-		//        coro::switchToMainFiber();
-		//        // Unreachable
-		//    }
-		//
-
-		sz::Call(::function, ::basicBlock, coro::setDone, this->handle);
-
-		// A Win32 Fiber function must not end, otherwise it tears down the thread it's running on.
-		// So we add code to switch back to the main thread.
-		sz::Call(::function, ::basicBlock, coro::switchToMainFiber, this->handle);
+		::basicBlock = resumeBlock;
 	}
 
 	using FunctionUniquePtr = std::unique_ptr<Ice::Cfg>;
@@ -4739,7 +4651,7 @@
 		//     {
 		//         YieldType* promise = coro::getPromisePtr(handle);
 		//         *out = *promise;
-		//         coro::switchToRoutineFiber(handle);
+		//         coro::resume(handle);
 		//         return true;
 		//     }
 		// }
@@ -4776,8 +4688,8 @@
 			auto store = Ice::InstStore::create(awaitFunc, promiseVal, outPtr);
 			resumeBlock->appendInst(store);
 
-			//         coro::switchToRoutineFiber(handle);
-			sz::Call(awaitFunc, resumeBlock, coro::switchToRoutineFiber, handle);
+			//         coro::resume(handle);
+			sz::Call(awaitFunc, resumeBlock, coro::resume, handle);
 
 			//         return true;
 			Ice::InstRet *ret = Ice::InstRet::create(awaitFunc, ::context->getConstantInt32(1));
@@ -4806,9 +4718,7 @@
 	{
 		// void coroutine_destroy(Nucleus::CoroutineHandle handle)
 		// {
-		//     coro::convertMainFiberToThread(coroData);
-		//     coro::deleteRoutineFiber(handle);
-		//     coro::destroyCoroutineData(handle);
+		//     coro::stop(handle); // signal and wait for coroutine to stop, and delete coroutine data
 		//     return;
 		// }
 
@@ -4822,14 +4732,8 @@
 
 		auto *bb = destroyFunc->getEntryNode();
 
-		//     coro::convertMainFiberToThread(coroData);
-		sz::Call(destroyFunc, bb, coro::convertMainFiberToThread, handle);
-
-		//     coro::deleteRoutineFiber(handle);
-		sz::Call(destroyFunc, bb, coro::deleteRoutineFiber, handle);
-
-		//     coro::destroyCoroutineData(handle);
-		sz::Call(destroyFunc, bb, coro::destroyCoroutineData, handle);
+		//     coro::stop(handle); // signal and wait for coroutine to stop, and delete coroutine data
+		sz::Call(destroyFunc, bb, coro::stop, handle);
 
 		//     return;
 		Ice::InstRet *ret = Ice::InstRet::create(destroyFunc);
@@ -4848,26 +4752,19 @@
 	// This doubles up as our coroutine handle
 	auto coroData = coro::createCoroutineData();
 
-	// Convert current thread to a fiber so we can create new fibers and switch to them
-	coro::convertThreadToMainFiber(coroData);
-
-	coro::FiberFunc fiberFunc = [&]() {
+	marl::schedule([=] {
 		// Store handle in TLS so that the coroutine can grab it right away, before
 		// any fiber switch occurs.
 		coro::setHandleParam(coroData);
 
-		// Invoke the begin function in the context of the routine fiber
 		beginFunc();
 
-		// Either it yielded, or finished. In either case, we switch back to the main fiber.
-		// We don't ever return from this function, or the current thread will be destroyed.
-		coro::switchToMainFiber(coroData);
-	};
+		coroData->done.signal();        // coroutine is done.
+		coroData->suspended.signal();   // resume any blocking await() call.
+		coroData->terminated.signal();  // signal that the coroutine data is ready for freeing.
+	});
 
-	coro::createRoutineFiber(coroData, &fiberFunc);
-
-	// Fiber will now start running, executing the saved beginFunc
-	coro::switchToRoutineFiber(coroData);
+	coroData->suspended.wait();  // block until the first yield or coroutine end
 
 	return coroData;
 }
@@ -4914,7 +4811,6 @@
 		// Finish generating coroutine functions
 		{
 			Ice::CfgLocalAllocatorScope scopedAlloc{ ::function };
-			::coroGen->generateCoroutineEnd();
 			createRetVoidIfNoRet();
 		}