From 7200f727e2656bd2f820b0266bd01ed7f7b14ed7 Mon Sep 17 00:00:00 2001
From: Dzmitry Malyshau <dmalyshau@mozilla.com>
Date: Tue, 23 Apr 2019 16:45:33 -0400
Subject: [PATCH] Expose device polling

---
 wgpu-bindings/wgpu.h      |  2 ++
 wgpu-native/src/device.rs | 18 ++++++++++++++++--
 wgpu-rs/src/lib.rs        | 10 ++++++++++
 3 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/wgpu-bindings/wgpu.h b/wgpu-bindings/wgpu.h
index 688cde37be..b413c5ab46 100644
--- a/wgpu-bindings/wgpu.h
+++ b/wgpu-bindings/wgpu.h
@@ -758,6 +758,8 @@ void wgpu_device_destroy(WGPUDeviceId device_id);
 
 WGPUQueueId wgpu_device_get_queue(WGPUDeviceId device_id);
 
+void wgpu_device_poll(WGPUDeviceId device_id);
+
 void wgpu_device_wait_idle(WGPUDeviceId device_id);
 
 WGPUSurfaceId wgpu_instance_create_surface_from_macos_layer(WGPUInstanceId instance_id,
diff --git a/wgpu-native/src/device.rs b/wgpu-native/src/device.rs
index fd78438470..2abdfb52bc 100644
--- a/wgpu-native/src/device.rs
+++ b/wgpu-native/src/device.rs
@@ -100,6 +100,15 @@ struct ActiveSubmission<B: hal::Backend> {
     mapped: Vec<BufferId>,
 }
 
+/// A class responsible for tracking resource lifetimes.
+///
+/// Here is how host mapping is handled:
+///   1. When mapping is requested we add the buffer to the pending list of `mapped` buffers.
+///   2. When `triage_referenced` is called, it checks the last submission index associated with each of the mapped buffer,
+/// and register the buffer with either a submission in flight, or straight into `ready_to_map` vector.
+///   3. when `ActiveSubmission` is retired, the mapped buffers associated with it are moved to `ready_to_map` vector.
+///   4. Finally, `handle_mapping` issues all the callbacks.
+
 struct DestroyedResources<B: hal::Backend> {
     /// Resources that the user has requested be mapped, but are still in use.
     mapped: Vec<Stored<BufferId>>,
@@ -222,8 +231,8 @@ impl DestroyedResources<back::Backend> {
 
         let buffer_guard = HUB.buffers.read();
 
-        for i in (0..self.mapped.len()).rev() {
-            let resource_id = self.mapped.swap_remove(i).value;
+        for stored in self.mapped.drain(..) {
+            let resource_id = stored.value;
             let buf = &buffer_guard[resource_id];
 
             let usage = match buf.pending_map_operation {
@@ -1818,6 +1827,11 @@ pub extern "C" fn wgpu_device_wait_idle(device_id: DeviceId) {
     device.maintain();
 }
 
+#[no_mangle]
+pub extern "C" fn wgpu_device_poll(device_id: DeviceId) {
+    HUB.devices.read()[device_id].maintain();
+}
+
 #[no_mangle]
 pub extern "C" fn wgpu_device_destroy(device_id: DeviceId) {
     let device = HUB.devices.unregister(device_id);
diff --git a/wgpu-rs/src/lib.rs b/wgpu-rs/src/lib.rs
index 66cbc7a2a7..1324214db0 100644
--- a/wgpu-rs/src/lib.rs
+++ b/wgpu-rs/src/lib.rs
@@ -285,6 +285,16 @@ impl Adapter {
 }
 
 impl Device {
+    /// Check for resource cleanups and mapping callbacks.
+    pub fn poll(&self) {
+        wgn::wgpu_device_poll(self.id);
+    }
+
+    /// Wait for GPU work to finish and process all the callbacks.
+    pub fn wait_idle(&self) {
+        wgn::wgpu_device_wait_idle(self.id);
+    }
+
     pub fn create_shader_module(&self, spv: &[u8]) -> ShaderModule {
         let desc = wgn::ShaderModuleDescriptor {
             code: wgn::ByteArray {