perf(server): post events and call libwayland without per-call allocations

commit: f0a709aaffee1dc6b87eeedb50c74cde659c35a0
author: brice · 25d ago · 2026-09-27 16:32 UTC
committer: brice · 25d ago · 2026-09-27 18:47 UTC
parent: d481123
signature: GPG VerifiedCD88F9E564E0102646FB6077A1A07C7C7C3E349D · arch-gpg Verified for the committer email

2 files · +31 -8

M server/display.go +11 -2


@@ -261,6 +261,12 @@ func (r *Resource) Destroy() {
261	261		}
262	262		}
263	263
	264	+	// eventArgs holds the wl_argument array of the event being posted.
	265	+	// libwayland copies it before wl_resource_post_event_array returns.
	266	+	// Display goroutine only; post_event_array does not call back into Go, so
	267	+	// PostEvent is not re-entrant. No protocol event has more than 8 arguments.
	268	+	var eventArgs [16]Arg
	269	+
264	270		// PostEvent sends an event. Arguments must match the event signature; build
265	271		// string and array arguments with a Pinner and unpin it after this returns.
266	272		// Calling it after destruction is safe and does nothing.

@@ -268,12 +274,15 @@ func (r *Resource) PostEvent(opcode uint32, args ...Arg) {
268	274		if r.gone {
269	275		return
270	276		}
	277	+	if len(args) > len(eventArgs) {
	278	+	panic("purego-libwayland: too many event arguments")
	279	+	}
271	280		var p unsafe.Pointer
272	281		if len(args) > 0 {
273		-	p = unsafe.Pointer(&args[0])
	282	+	copy(eventArgs[:], args)
	283	+	p = unsafe.Pointer(&eventArgs[0])
274	284		}
275	285		wlResourcePostEventArr(r.c, opcode, p)
276		-	runtime.KeepAlive(args)
277	286		}
278	287
279	288		// PostError sends a protocol error and disconnects the client.

 	}
 }
+// eventArgs holds the wl_argument array of the event being posted.
+// libwayland copies it before wl_resource_post_event_array returns.
+// Display goroutine only; post_event_array does not call back into Go, so
+// PostEvent is not re-entrant. No protocol event has more than 8 arguments.
+var eventArgs [16]Arg
 // PostEvent sends an event. Arguments must match the event signature; build
 // string and array arguments with a Pinner and unpin it after this returns.
 // Calling it after destruction is safe and does nothing.
 	if r.gone {
 		return
 	}
+	if len(args) > len(eventArgs) {
+		panic("purego-libwayland: too many event arguments")
+	}
 	var p unsafe.Pointer
 	if len(args) > 0 {
-		p = unsafe.Pointer(&args[0])
+		copy(eventArgs[:], args)
+		p = unsafe.Pointer(&eventArgs[0])
 	}
 	wlResourcePostEventArr(r.c, opcode, p)
-	runtime.KeepAlive(args)
 }
 // PostError sends a protocol error and disconnects the client.

M server/lib.go +20 -6


@@ -90,20 +90,34 @@ func load() error {
90	90		return loadErr
91	91		}
92	92
	93	+	// callArgs is scratch for SyscallN so hot calls do not allocate a variadic
	94	+	// slice. Display goroutine only; all libwayland calls run there.
	95	+	var callArgs [6]uintptr
	96	+
93	97		// Integer and pointer-only entry points avoid RegisterLibFunc's reflective call path.
94		-	func wlDisplayFlushClients(display uintptr) { purego.SyscallN(symDisplayFlushClients, display) }
	98	+	func wlDisplayFlushClients(display uintptr) {
	99	+	callArgs[0] = display
	100	+	purego.SyscallN(symDisplayFlushClients, callArgs[:1]...)
	101	+	}
95	102		func wlEventLoopDispatch(loop uintptr, timeout int32) int32 {
96		-	r, _, _ := purego.SyscallN(symEventLoopDispatch, loop, uintptr(timeout))
	103	+	callArgs[0], callArgs[1] = loop, uintptr(timeout)
	104	+	r, _, _ := purego.SyscallN(symEventLoopDispatch, callArgs[:2]...)
97	105		return int32(r)
98	106		}
99	107		func wlResourceCreate(client, iface uintptr, version int32, id uint32) uintptr {
100		-	r, _, _ := purego.SyscallN(symResourceCreate, client, iface, uintptr(version), uintptr(id))
	108	+	callArgs[0], callArgs[1], callArgs[2], callArgs[3] = client, iface, uintptr(version), uintptr(id)
	109	+	r, _, _ := purego.SyscallN(symResourceCreate, callArgs[:4]...)
101	110		return r
102	111		}
103	112		func wlResourceSetDispatcher(resource, dispatcher, impl, data, destroy uintptr) {
104		-	purego.SyscallN(symResourceSetDispatcher, resource, dispatcher, impl, data, destroy)
	113	+	callArgs[0], callArgs[1], callArgs[2], callArgs[3], callArgs[4] = resource, dispatcher, impl, data, destroy
	114	+	purego.SyscallN(symResourceSetDispatcher, callArgs[:5]...)
105	115		}
106	116		func wlResourcePostEventArr(resource uintptr, opcode uint32, args unsafe.Pointer) {
107		-	purego.SyscallN(symResourcePostEventArr, resource, uintptr(opcode), uintptr(args))
	117	+	callArgs[0], callArgs[1], callArgs[2] = resource, uintptr(opcode), uintptr(args)
	118	+	purego.SyscallN(symResourcePostEventArr, callArgs[:3]...)
	119	+	}
	120	+	func wlResourceDestroy(resource uintptr) {
	121	+	callArgs[0] = resource
	122	+	purego.SyscallN(symResourceDestroy, callArgs[:1]...)
108	123		}
109		-	func wlResourceDestroy(resource uintptr) { purego.SyscallN(symResourceDestroy, resource) }

 	return loadErr
 }
+// callArgs is scratch for SyscallN so hot calls do not allocate a variadic
+// slice. Display goroutine only; all libwayland calls run there.
+var callArgs [6]uintptr
 // Integer and pointer-only entry points avoid RegisterLibFunc's reflective call path.
-func wlDisplayFlushClients(display uintptr) { purego.SyscallN(symDisplayFlushClients, display) }
+func wlDisplayFlushClients(display uintptr) {
+	callArgs[0] = display
+	purego.SyscallN(symDisplayFlushClients, callArgs[:1]...)
+}
 func wlEventLoopDispatch(loop uintptr, timeout int32) int32 {
-	r, _, _ := purego.SyscallN(symEventLoopDispatch, loop, uintptr(timeout))
+	callArgs[0], callArgs[1] = loop, uintptr(timeout)
+	r, _, _ := purego.SyscallN(symEventLoopDispatch, callArgs[:2]...)
 	return int32(r)
 }
 func wlResourceCreate(client, iface uintptr, version int32, id uint32) uintptr {
-	r, _, _ := purego.SyscallN(symResourceCreate, client, iface, uintptr(version), uintptr(id))
+	callArgs[0], callArgs[1], callArgs[2], callArgs[3] = client, iface, uintptr(version), uintptr(id)
+	r, _, _ := purego.SyscallN(symResourceCreate, callArgs[:4]...)
 	return r
 }
 func wlResourceSetDispatcher(resource, dispatcher, impl, data, destroy uintptr) {
-	purego.SyscallN(symResourceSetDispatcher, resource, dispatcher, impl, data, destroy)
+	callArgs[0], callArgs[1], callArgs[2], callArgs[3], callArgs[4] = resource, dispatcher, impl, data, destroy
+	purego.SyscallN(symResourceSetDispatcher, callArgs[:5]...)
 }
 func wlResourcePostEventArr(resource uintptr, opcode uint32, args unsafe.Pointer) {
-	purego.SyscallN(symResourcePostEventArr, resource, uintptr(opcode), uintptr(args))
+	callArgs[0], callArgs[1], callArgs[2] = resource, uintptr(opcode), uintptr(args)
+	purego.SyscallN(symResourcePostEventArr, callArgs[:3]...)
+}
+func wlResourceDestroy(resource uintptr) {
+	callArgs[0] = resource
+	purego.SyscallN(symResourceDestroy, callArgs[:1]...)
 }
-func wlResourceDestroy(resource uintptr) { purego.SyscallN(symResourceDestroy, resource) }