[core] Avoid blocking in Thread<Object> constructor (#12151)

* Introduce AspiringActor, EstablishedActor

This pair of objects represents the two-phase (parent-thread /
child-thread) construction that's needed to support constructing
Thread<Object> without blocking until the child thread is up and
running.

An `AspiringActor<O>` is responsible for:
 - ownership of the actor's `Mailbox`
 - allocating the memory for (but *not* constructing) the target object `O`

Using these two pieces--the mailbox and a stable address for `O`--an
`AspiringActor<O>` can accept messages for the target object, or provide
`ActorRef<O>`s that do so, before the object has actually been
constructed by the corresponding `EstablishedActor<O>`.  (Such messages
are queued in the mailbox until after the object is constructed.)

This allows for an `AspiringActor<O>` to be created and safely used by a
thread other than the one on which the target object will (eventually)
live.

An `EstablishedActor<O>` is responsible for managing the lifetime of the
target object `O` and the open/closed state of the parent's `mailbox`.

The `O` object's lifetime is contained by that of its owning
`EstablishedActor<O>`: the `EstablishedActor` constructor executes the
`O` constructor via "placement new", constructing it at the address
provided by the parent `AspiringActor`, and the `~EstablishedActor`
destructor similarly executes the `~O` destructor (after closing the
mailbox). `EstablishedActor` should therefore live entirely on the
thread intended to own `O`.

* Remove Actor#{invoke,ask}

1 files changed, 5 insertions, 5 deletions

diff --git a/src/mbgl/tile/geometry_tile.cpp b/src/mbgl/tile/geometry_tile.cpp
index af28fe3963..d686d8440b 100644
--- a/src/mbgl/tile/geometry_tile.cpp
+++ b/src/mbgl/tile/geometry_tile.cpp
@@ -86,7 +86,7 @@ void GeometryTile::setData(std::unique_ptr<const GeometryTileData> data_) {
     pending = true;
 
     ++correlationID;
-    worker.invoke(&GeometryTileWorker::setData, std::move(data_), correlationID);
+    worker.self().invoke(&GeometryTileWorker::setData, std::move(data_), correlationID);
 }
 
 
@@ -112,14 +112,14 @@ void GeometryTile::setLayers(const std::vector<Immutable<Layer::Impl>>& layers)
     }
 
     ++correlationID;
-    worker.invoke(&GeometryTileWorker::setLayers, std::move(impls), correlationID);
+    worker.self().invoke(&GeometryTileWorker::setLayers, std::move(impls), correlationID);
 }
 
 void GeometryTile::setShowCollisionBoxes(const bool showCollisionBoxes_) {
     if (showCollisionBoxes != showCollisionBoxes_) {
         showCollisionBoxes = showCollisionBoxes_;
         ++correlationID;
-        worker.invoke(&GeometryTileWorker::setShowCollisionBoxes, showCollisionBoxes, correlationID);
+        worker.self().invoke(&GeometryTileWorker::setShowCollisionBoxes, showCollisionBoxes, correlationID);
     }
 }
 
@@ -153,7 +153,7 @@ void GeometryTile::onError(std::exception_ptr err, const uint64_t resultCorrelat
 }
     
 void GeometryTile::onGlyphsAvailable(GlyphMap glyphs) {
-    worker.invoke(&GeometryTileWorker::onGlyphsAvailable, std::move(glyphs));
+    worker.self().invoke(&GeometryTileWorker::onGlyphsAvailable, std::move(glyphs));
 }
 
 void GeometryTile::getGlyphs(GlyphDependencies glyphDependencies) {
@@ -161,7 +161,7 @@ void GeometryTile::getGlyphs(GlyphDependencies glyphDependencies) {
 }
 
 void GeometryTile::onImagesAvailable(ImageMap images, uint64_t imageCorrelationID) {
-    worker.invoke(&GeometryTileWorker::onImagesAvailable, std::move(images), imageCorrelationID);
+    worker.self().invoke(&GeometryTileWorker::onImagesAvailable, std::move(images), imageCorrelationID);
 }
 
 void GeometryTile::getImages(ImageRequestPair pair) {