[common] fix fibers by using older boost instead of minicoro (#2665)

Revert of a previous commit that added minicoro for a reason god knows why

Signed-off-by: lizzie <lizzie@eden-emu.dev>

Co-authored-by: Caio Oliveira <caiooliveirafarias0@gmail.com>
Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/2665
Reviewed-by: DraVee <dravee@eden-emu.dev>
Reviewed-by: Maufeat <sahyno1996@gmail.com>
Co-authored-by: lizzie <lizzie@eden-emu.dev>
Co-committed-by: lizzie <lizzie@eden-emu.dev>

1 files changed, 88 insertions, 69 deletions

diff --git a/src/common/fiber.cpp b/src/common/fiber.cpp
index 8c3bae7c16..4f0f2b6430 100644
--- a/src/common/fiber.cpp
+++ b/src/common/fiber.cpp
@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
 // SPDX-FileCopyrightText: Copyright 2020 yuzu Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
@@ -5,47 +8,87 @@
 
 #include "common/assert.h"
 #include "common/fiber.h"
-#define MCO_USE_VMEM_ALLOCATOR
-#define MINICORO_IMPL
-#include "common/minicoro.h"
+#include "common/virtual_buffer.h"
+
+#include <boost/context/detail/fcontext.hpp>
 
 namespace Common {
 
+constexpr std::size_t default_stack_size = 512 * 1024;
+
 struct Fiber::FiberImpl {
-    FiberImpl() {}
+    FiberImpl() : stack{default_stack_size}, rewind_stack{default_stack_size} {}
+
+    VirtualBuffer<u8> stack;
+    VirtualBuffer<u8> rewind_stack;
 
     std::mutex guard;
-    bool released{};
-    bool is_thread_fiber{};
-    Fiber* next_fiber{};
-    Fiber** next_fiber_ptr;
     std::function<void()> entry_point;
+    std::function<void()> rewind_point;
+    std::shared_ptr<Fiber> previous_fiber;
+    bool is_thread_fiber{};
+    bool released{};
 
-    mco_coro* context;
+    u8* stack_limit{};
+    u8* rewind_stack_limit{};
+    boost::context::detail::fcontext_t context{};
+    boost::context::detail::fcontext_t rewind_context{};
 };
 
-Fiber::Fiber() : impl{std::make_unique<FiberImpl>()} {
-    impl->is_thread_fiber = true;
+void Fiber::SetRewindPoint(std::function<void()>&& rewind_func) {
+    impl->rewind_point = std::move(rewind_func);
+}
+
+void Fiber::Start(boost::context::detail::transfer_t& transfer) {
+    ASSERT(impl->previous_fiber != nullptr);
+    impl->previous_fiber->impl->context = transfer.fctx;
+    impl->previous_fiber->impl->guard.unlock();
+    impl->previous_fiber.reset();
+    impl->entry_point();
+    UNREACHABLE();
+}
+
+void Fiber::OnRewind([[maybe_unused]] boost::context::detail::transfer_t& transfer) {
+    ASSERT(impl->context != nullptr);
+    impl->context = impl->rewind_context;
+    impl->rewind_context = nullptr;
+    u8* tmp = impl->stack_limit;
+    impl->stack_limit = impl->rewind_stack_limit;
+    impl->rewind_stack_limit = tmp;
+    impl->rewind_point();
+    UNREACHABLE();
+}
+
+void Fiber::FiberStartFunc(boost::context::detail::transfer_t transfer) {
+    auto* fiber = static_cast<Fiber*>(transfer.data);
+    fiber->Start(transfer);
+}
+
+void Fiber::RewindStartFunc(boost::context::detail::transfer_t transfer) {
+    auto* fiber = static_cast<Fiber*>(transfer.data);
+    fiber->OnRewind(transfer);
 }
 
 Fiber::Fiber(std::function<void()>&& entry_point_func) : impl{std::make_unique<FiberImpl>()} {
     impl->entry_point = std::move(entry_point_func);
-    auto desc = mco_desc_init(
-        [](mco_coro* coro) { reinterpret_cast<Fiber*>(coro->user_data)->impl->entry_point(); }, 0);
-    desc.user_data = this;
-    mco_result res = mco_create(&impl->context, &desc);
-    ASSERT(res == MCO_SUCCESS);
+    impl->stack_limit = impl->stack.data();
+    impl->rewind_stack_limit = impl->rewind_stack.data();
+    u8* stack_base = impl->stack_limit + default_stack_size;
+    impl->context =
+        boost::context::detail::make_fcontext(stack_base, impl->stack.size(), FiberStartFunc);
 }
 
+Fiber::Fiber() : impl{std::make_unique<FiberImpl>()} {}
+
 Fiber::~Fiber() {
     if (impl->released) {
         return;
     }
-    DestroyPre();
-    if (impl->is_thread_fiber) {
-        DestroyThreadFiber();
-    } else {
-        DestroyWorkFiber();
+    // Make sure the Fiber is not being used
+    const bool locked = impl->guard.try_lock();
+    ASSERT_MSG(locked, "Destroying a fiber that's still running");
+    if (locked) {
+        impl->guard.unlock();
     }
 }
 
@@ -54,66 +97,42 @@ void Fiber::Exit() {
     if (!impl->is_thread_fiber) {
         return;
     }
-    DestroyPre();
-    DestroyThreadFiber();
-}
-
-void Fiber::DestroyPre() {
-    // Make sure the Fiber is not being used
-    const bool locked = impl->guard.try_lock();
-    ASSERT_MSG(locked, "Destroying a fiber that's still running");
-    if (locked) {
-        impl->guard.unlock();
-    }
+    impl->guard.unlock();
     impl->released = true;
 }
 
-void Fiber::DestroyWorkFiber() {
-    mco_result res = mco_destroy(impl->context);
-    ASSERT(res == MCO_SUCCESS);
-}
-
-void Fiber::DestroyThreadFiber() {
-    if (*impl->next_fiber_ptr) {
-        *impl->next_fiber_ptr = nullptr;
-    }
+void Fiber::Rewind() {
+    ASSERT(impl->rewind_point);
+    ASSERT(impl->rewind_context == nullptr);
+    u8* stack_base = impl->rewind_stack_limit + default_stack_size;
+    impl->rewind_context =
+        boost::context::detail::make_fcontext(stack_base, impl->stack.size(), RewindStartFunc);
+    boost::context::detail::jump_fcontext(impl->rewind_context, this);
 }
 
 void Fiber::YieldTo(std::weak_ptr<Fiber> weak_from, Fiber& to) {
+    to.impl->guard.lock();
+    to.impl->previous_fiber = weak_from.lock();
+
+    auto transfer = boost::context::detail::jump_fcontext(to.impl->context, &to);
+
+    // "from" might no longer be valid if the thread was killed
     if (auto from = weak_from.lock()) {
-        if (!from->impl->is_thread_fiber) {
-            // Set next fiber
-            from->impl->next_fiber = &to;
-            // Yield from thread
-            if (!from->impl->released) {
-                from->impl->guard.unlock();
-                mco_yield(from->impl->context);
-            }
-        } else {
-            from->impl->guard.lock();
-            // Keep running next fiber until they've ran out
-            auto& next_fiber_ptr = from->impl->next_fiber_ptr;
-            next_fiber_ptr = &from->impl->next_fiber;
-            *next_fiber_ptr = &to;
-            for ([[maybe_unused]] unsigned round = 0; *next_fiber_ptr; round++) {
-                auto next = *next_fiber_ptr;
-                *next_fiber_ptr = nullptr;
-                next_fiber_ptr = &next->impl->next_fiber;
-                // Stop if new thread is thread fiber
-                if (next->impl->is_thread_fiber)
-                    break;
-                // Resume new thread
-                next->impl->guard.lock();
-                mco_result res = mco_resume(next->impl->context);
-                ASSERT(res == MCO_SUCCESS);
-            }
-            from->impl->guard.unlock();
+        if (from->impl->previous_fiber == nullptr) {
+            ASSERT_MSG(false, "previous_fiber is nullptr!");
+            return;
         }
+        from->impl->previous_fiber->impl->context = transfer.fctx;
+        from->impl->previous_fiber->impl->guard.unlock();
+        from->impl->previous_fiber.reset();
     }
 }
 
 std::shared_ptr<Fiber> Fiber::ThreadToFiber() {
-    return std::shared_ptr<Fiber>{new Fiber()};
+    std::shared_ptr<Fiber> fiber = std::shared_ptr<Fiber>{new Fiber()};
+    fiber->impl->guard.lock();
+    fiber->impl->is_thread_fiber = true;
+    return fiber;
 }
 
 } // namespace Common