Implement Fiber and Scheduler for win32

The actual stack context switch is still missing.

src/concurrent.cr

@@ -3,6 +3,7 @@ require "channel"
 require "crystal/scheduler"
 require "./concurrent/*"
 
+{% unless flag?(:win32) %}
 # Blocks the current fiber for the specified number of seconds.
 #
 # While this fiber is waiting this time other ready-to-execute
@@ -22,6 +23,7 @@ end
 def sleep(time : Time::Span)
   Crystal::Scheduler.sleep(time)
 end
+{% end %}
 
 # Blocks the current fiber forever.
 #

src/crystal/scheduler.cr

@@ -68,7 +68,14 @@ class Crystal::Scheduler
     if runnable = @runnables.shift?
       runnable.resume
     else
-      Crystal::EventLoop.resume
+      {% if flag?(:unix) %}
+        Crystal::EventLoop.resume
+      {% elsif flag?(:win32) %}
+        STDERR.puts "Warning: No runnables in scheduler. Exiting program."
+        ::exit
+      {% else %}
+        {% raise "unsupported platform" %}
+      {% end %}
     end
   end
 
@@ -78,11 +85,25 @@ class Crystal::Scheduler
   end
 
   protected def yield : Nil
-    sleep(0.seconds)
+    {% if flag?(:unix) %}
+      sleep(0.seconds)
+    {% elsif flag?(:win32) %}
+      @runnables << @current
+      reschedule
+    {% else %}
+      {% raise "unsupported platform" %}
+    {% end %}
   end
 
   protected def yield(fiber : Fiber) : Nil
-    @current.resume_event.add(0.seconds)
+    {% if flag?(:unix) %}
+      @current.resume_event.add(0.seconds)
+    {% elsif flag?(:win32) %}
+      @runnables << fiber
+    {% else %}
+      {% raise "unsupported platform" %}
+    {% end %}
+
     resume(fiber)
   end
 end

src/crystal/system/fiber.cr

@@ -11,6 +11,8 @@ end
 
 {% if flag?(:unix) %}
   require "./unix/fiber"
+{% elsif flag?(:win32) %}
+  require "./win32/fiber"
 {% else %}
   {% raise "fiber not supported" %}
 {% end %}

src/crystal/system/win32/fiber.cr

@@ -0,0 +1,27 @@
+require "c/winbase"
+require "c/winnt"
+require "c/processthreadsapi"
+
+module Crystal::System::Fiber
+  def self.allocate_stack(stack_size) : Void*
+    memory_pointer = LibC.VirtualAlloc(nil, stack_size, LibC::MEM_COMMIT | LibC::MEM_RESERVE, LibC::PAGE_READWRITE)
+
+    if memory_pointer.null?
+      raise WinError.new("VirtualAlloc")
+    end
+
+    memory_pointer
+  end
+
+  def self.free_stack(stack : Void*, stack_size) : Nil
+    if LibC.VirtualFree(stack, stack_size, LibC::MEM_RELEASE) == 0
+      raise WinError.new("VirtualFree")
+    end
+  end
+
+  def self.main_fiber_stack(stack_bottom : Void*) : Void*
+    LibC.GetCurrentThreadStackLimits(out lowLimit, out highLimit)
+
+    Pointer(Void).new(lowLimit)
+  end
+end

src/fiber.cr

@@ -48,7 +48,11 @@ class Fiber
   @@stack_pool = [] of Void*
 
   @stack : Void*
+
+  {% unless flag?(:win32) %}
   @resume_event : Crystal::Event?
+  {% end %}
+
   @stack_top = Pointer(Void).null
   protected property stack_top : Void*
   protected property stack_bottom : Void*
@@ -130,8 +134,10 @@ class Fiber
     # Remove the current fiber from the linked list
     @@fibers.delete(self)
 
+    {% unless flag?(:win32) %}
     # Delete the resume event if it was used by `yield` or `sleep`
     @resume_event.try &.free
+    {% end %}
 
     Crystal::Scheduler.reschedule
   end
@@ -144,10 +150,12 @@ class Fiber
     Crystal::Scheduler.resume(self)
   end
 
+  {% unless flag?(:win32) %}
   # :nodoc:
   def resume_event
     @resume_event ||= Crystal::EventLoop.create_resume_event(self)
   end
+  {% end %}
 
   def self.yield
     Crystal::Scheduler.yield

src/kernel.cr

@@ -470,15 +470,15 @@ class Process
   end
 end
 
-{% unless flag?(:win32) %}
-  # Background loop to cleanup unused fiber stacks.
-  spawn do
-    loop do
-      sleep 5
-      Fiber.stack_pool_collect
-    end
+# Background loop to cleanup unused fiber stacks.
+spawn do
+  loop do
+    sleep 5
+    Fiber.stack_pool_collect
   end
+end
 
+{% unless flag?(:win32) %}
   Signal.setup_default_handlers
   LibExt.setup_sigfault_handler
 {% end %}

src/lib_c/x86_64-windows-msvc/c/basetsd.cr

@@ -4,4 +4,5 @@ lib LibC
   {% else %}
     alias ULONG_PTR = ULong
   {% end %}
+  alias PULONG_PTR = ULONG_PTR*
 end

src/lib_c/x86_64-windows-msvc/c/processthreadsapi.cr

@@ -0,0 +1,5 @@
+require "./basetsd"
+
+lib LibC
+  fun GetCurrentThreadStackLimits(lowLimit : PULONG_PTR, highLimit : PULONG_PTR) : Void
+end

src/lib_c/x86_64-windows-msvc/c/winbase.cr

@@ -90,4 +90,16 @@ lib LibC
   fun GetEnvironmentStringsW : LPWCH
   fun FreeEnvironmentStringsW(lpszEnvironmentBlock : LPWCH) : BOOL
   fun SetEnvironmentVariableW(lpName : LPWSTR, lpValue : LPWSTR) : BOOL
+
+  MEM_COMMIT     = 0x00001000
+  MEM_RESERVE    = 0x00002000
+  MEM_RESET      = 0x00080000
+  MEM_RESET_UNDO = 0x01000000
+
+  fun VirtualAlloc(lpAddress : Void*, dwSize : SizeT, flAllocationType : DWORD, flProtect : DWORD) : Void*
+
+  MEM_DECOMMIT = 0x4000
+  MEM_RELEASE  = 0x8000
+
+  fun VirtualFree(lpAddress : Void*, dwSize : SizeT, dwFreeType : DWORD) : BOOL
 end

src/lib_c/x86_64-windows-msvc/c/winnt.cr

@@ -16,4 +16,7 @@ lib LibC
   FILE_ATTRIBUTE_REPARSE_POINT = 0x400
 
   FILE_READ_ATTRIBUTES = 0x80
+
+  # Memory protection constants
+  PAGE_READWRITE = 0x04
 end

src/prelude.cr

@@ -35,7 +35,7 @@ require "box"
 require "char"
 require "char/reader"
 require "class"
-no_win require "concurrent"
+require "concurrent"
 require "crystal/main"
 require "deque"
 require "dir"