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author | Anand Thakker <anandthakker@users.noreply.github.com> | 2018-07-03 17:17:39 -0400 |
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committer | GitHub <noreply@github.com> | 2018-07-03 17:17:39 -0400 |
commit | cfd436c287f4209d0d994042452ccbb552a6bd28 (patch) | |
tree | 6811590928d7ea19db8e8b3f9db8d1df54ba9965 /src/mbgl/actor | |
parent | 840a5cf1207ed78df3302211a23d369dd3c12b89 (diff) | |
download | qtlocation-mapboxgl-cfd436c287f4209d0d994042452ccbb552a6bd28.tar.gz |
[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}
Diffstat (limited to 'src/mbgl/actor')
-rw-r--r-- | src/mbgl/actor/mailbox.cpp | 35 |
1 files changed, 31 insertions, 4 deletions
diff --git a/src/mbgl/actor/mailbox.cpp b/src/mbgl/actor/mailbox.cpp index 373c24275f..8ee8dca114 100644 --- a/src/mbgl/actor/mailbox.cpp +++ b/src/mbgl/actor/mailbox.cpp @@ -6,8 +6,30 @@ namespace mbgl { +Mailbox::Mailbox() { +} + Mailbox::Mailbox(Scheduler& scheduler_) - : scheduler(scheduler_) { + : scheduler(&scheduler_) { +} + +void Mailbox::open(Scheduler& scheduler_) { + assert(!scheduler); + + // As with close(), block until neither receive() nor push() are in progress, and acquire the two + // mutexes in the same order. + std::lock_guard<std::recursive_mutex> receivingLock(receivingMutex); + std::lock_guard<std::mutex> pushingLock(pushingMutex); + + scheduler = &scheduler_; + + if (closed) { + return; + } + + if (!queue.empty()) { + (*scheduler)->schedule(shared_from_this()); + } } void Mailbox::close() { @@ -22,6 +44,9 @@ void Mailbox::close() { closed = true; } +bool Mailbox::isOpen() const { return bool(scheduler); } + + void Mailbox::push(std::unique_ptr<Message> message) { std::lock_guard<std::mutex> pushingLock(pushingMutex); @@ -32,13 +57,15 @@ void Mailbox::push(std::unique_ptr<Message> message) { std::lock_guard<std::mutex> queueLock(queueMutex); bool wasEmpty = queue.empty(); queue.push(std::move(message)); - if (wasEmpty) { - scheduler.schedule(shared_from_this()); + if (wasEmpty && scheduler) { + (*scheduler)->schedule(shared_from_this()); } } void Mailbox::receive() { std::lock_guard<std::recursive_mutex> receivingLock(receivingMutex); + + assert(scheduler); if (closed) { return; @@ -58,7 +85,7 @@ void Mailbox::receive() { (*message)(); if (!wasEmpty) { - scheduler.schedule(shared_from_this()); + (*scheduler)->schedule(shared_from_this()); } } |