57 lines
1.9 KiB
C
57 lines
1.9 KiB
C
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// This file implements the C side of WinRT events.
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// Unfortunately, this cannot be done entirely in pure go, for two reasons:
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// * An Event object must be shared with the C world (WinRT) after
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// syscall.Syscall returns. This is not allowed in Go, to keep the option
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// open to switch to a moving GC in the future. For this, it is needed to
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// allocate the Event object on the C heap (using malloc).
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// * Building a virtual function table is very difficult (if not impossible)
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// in pure Go. It might be possible using reflect, but due the the previous
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// issue I haven't investigated that.
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#include <stdint.h>
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// Note: these functions have a different signature but because they are only
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// used as function pointers (and never called) and because they use C name
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// mangling, the signature doesn't really matter.
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void winbt_Event_Invoke(void);
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void winbt_Event_QueryInterface(void);
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// This is the contract the functions below should adhere to:
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// https://docs.microsoft.com/en-us/windows/win32/api/unknwn/nn-unknwn-iunknown
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static uint64_t winbt_Event_AddRef(void) {
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// This is safe, see winbt_Event_Release.
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return 2;
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}
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static uint64_t winbt_Event_Release(void) {
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// Pretend there is one reference left.
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// The docs say:
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// > This value is intended to be used only for test purposes.
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// Also see:
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// https://docs.microsoft.com/en-us/archive/msdn-magazine/2013/august/windows-with-c-the-windows-runtime-application-model
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return 1;
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}
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// The Vtable structure for WinRT event interfaces.
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typedef struct {
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void *QueryInterface;
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void *AddRef;
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void *Release;
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void *Invoke;
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} EventVtbl_t;
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// The Vtable itself. It can be kept constant.
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static const EventVtbl_t winbt_EventVtbl = {
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(void*)winbt_Event_QueryInterface,
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(void*)winbt_Event_AddRef,
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(void*)winbt_Event_Release,
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(void*)winbt_Event_Invoke,
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};
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// A small helper function to get the Vtable.
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const EventVtbl_t * winbt_getEventVtbl(void) {
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return &winbt_EventVtbl;
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}
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