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2023-11-29Merge branch 'DRTVWR-559' into marchcat/587-v-pbr-mergeAndrey Lihatskiy
# Conflicts: # indra/llcommon/CMakeLists.txt # indra/newview/llspatialpartition.cpp # indra/newview/llviewergenericmessage.cpp # indra/newview/llvoavatar.cpp
2023-10-29DRTVWR-587: Fix LL::apply(function, LLSD array).Nat Goodspeed
We define a specialization of LLSDParam<const char*> to support passing an LLSD object to a const char* function parameter. Needless to remark, passing object.asString().c_str() would be Bad: destroying the temporary std::string returned by asString() would immediately invalidate the pointer returned by its c_str(). But when you pass LLSDParam<const char*>(object) as the parameter, that specialization itself stores the std::string so the c_str() pointer remains valid as long as the LLSDParam object does. Then there's LLSDParam<LLSD>, used when we don't have the parameter type available to select the LLSDParam specialization. LLSDParam<LLSD> defines a templated conversion operator T() that constructs an LLSDParam<T> to provide the actual parameter value. So far, so good. The trouble was with the implementation of LLSDParam<LLSD>: it constructed a _temporary_ LLSDParam<T>, implicitly called its operator T() and immediately destroyed it. Destroying LLSDParam<const char*> destroyed its stored string, thus invalidating the c_str() pointer before the target function was entered. Instead, make LLSDParam<LLSD>::operator T() capture each LLSDParam<T> it constructs, extending its lifespan to the lifespan of the LLSDParam<LLSD> instance. For this, derive each LLSDParam specialization from LLSDParamBase, a trivial base class that simply establishes the virtual destructor. We can then capture any specialization as a pointer to LLSDParamBase. Also restore LazyEventAPI tests on Mac.
2023-07-27DRTVWR-587: Disable LazyEventAPI tests on TeamCity Macs.Nat Goodspeed
There's a limit to how much time it's worth trying to work around a compiler bug that's already been fixed in newer Xcode.
2023-07-18Merge pull request #280 from secondlife/dispatch-maint-v2nat-goodspeed
Major improvements to LLLeap functionality
2023-07-17Merge remote-tracking branch 'origin/main' into DRTVWR-559Brad Linden
2023-07-13DRTVWR-558: Extend LLEventDispatcher::add() overloads.Nat Goodspeed
Add LL::always_return<T>(), which takes a callable and variadic arguments. It calls the callable with those arguments and, if the returned type is convertible to T, converts it and returns it. Otherwise it returns T(). always_return() is generalized from, and supersedes, LLEventDispatcher::ReturnLLSD. Add LL::function_arity<CALLABLE>, which extends boost::function_types::function_arity by reporting results for both std::function<CALLABLE> and boost::function<CALLABLE>. Use for LL::apply(function, LLSD array) as well as for LLEventDispatcher. Make LLEventDispatcher::add() overloads uniformly distinguish between a callable (whether non-static member function or otherwise) that accepts a single LLSD parameter, versus any other signature. Accepting exactly one LLSD parameter signals that the callable will accept the composite arguments LLSD blob, instead of asking LLEventDispatcher to unpack the arguments blob into individual arguments. Support add(subclass method) overloads for arbitrary-parameters methods as well as for (const LLSD&) methods. Update tests accordingly: we need no longer pass the boilerplate lambda instance getter that binds and returns 'this'. Extract to the two LLEventDispatcher::make_invoker() overloads the LL::apply() logic formerly found in ReturnLLSD. Change lleventdispatcher_test.cpp tests from boost::bind(), which accepts variadic arguments (even though it only passes a fixed set to the target callable), to fixed-signature lambdas. This is because the revamped add() overloads care about signature. Add a test for a non-static method that accepts (const LLSD&), in other words the composite arguments LLSD blob, and likewise returns LLSD. (cherry picked from commit 95b787f7d7226ee9de79dfc9816f33c8bf199aad)
2023-07-13DRTVWR-558: LLEventDispatcher uses LL::apply(), not boost::fusion.Nat Goodspeed
While calling a C++ function with arguments taken from a runtime-variable data structure necessarily involves a bit of hocus-pocus, the best you can say for the boost::fusion based implementation is that it worked. Sadly, template recursion limited its applicability to a handful of function arguments. Now that we have LL::apply(), use that instead. This implementation is much more straightforward. In particular, the LLSDArgsSource class, whose job was to dole out elements of an LLSD array one at a time for the template recursion, goes away entirely. Make virtual LLEventDispatcher::DispatchEntry::call() return LLSD instead of void. All LLEventDispatcher target functions so far have been void; any function that wants to respond to its invoker must do so explicitly by calling sendReply() or constructing an LLEventAPI::Response instance. Supporting non- void functions permits LLEventDispatcher to respond implicitly with the returned value. Of course this requires a wrapper for void target functions that returns LLSD::isUndefined(). Break out LLEventDispatcher::reply() from callFail(), so we can reply with success as well as failure. Make LLEventDispatcher::try_call_log() prepend the actual leaf class name and description to any error returned by three-arg try_call(). That try_call() overload reported "LLEventDispatcher(desc): " for a couple specific errors, but no others. Hoist to try_call_log() to apply uniformly. Introduce new try_call_one() method to diagnose name-not-found errors and catch internal DispatchError and LL::apply_error exceptions. try_call_one() returns a std::pair, containing either an error message or an LLSD value. Make try_call_log() and three-arg try_call() accept LLSD 'name' instead of plain std::string, allowing for the possibility of an array or map. That lets us extend three-arg try_call() to break out new cases for the function selector LLSD: isUndefined(), isArray(), isMap() and (current case) scalar String. If try_call_one() reports an error, log it and try to send reply, as now. If it returns LLSD::isUndefined(), e.g. from a void target function wrapper, do nothing. But if it returns an LLSD map, try to send that back to the invoker. And if it returns an LLSD scalar or array, wrap it in a map with key "data" to respond to the invoker. Allowing a target function to return its result rather than explicitly sending it opens the possibility of batched requests (aggregate 'name') returning batched responses. Almost every place that constructs LLEventDispatcher's internal DispatchError exception called stringize() to format the what() string. Simplify calls by making DispatchError accept variadic arguments and forward to stringize(). Add LL::invoke() to apply.h. Like LL::apply(), this is a (limited) C++14 foreshadowing of std::invoke(), with preprocessor conditionals to switch to std::invoke() when that's available. Introduce LL::invoke() to handle a callable that's actually a pointer to method. Now our C++14 apply() implementation can accept pointer to method, using invoke() to generalize the actual function call. Also anticipate std::bind_front() with LL::bind_front(). For apply(func, std::array) and our extensions apply(func, std::vector) and apply(func, LLSD), we can't pass a pointer to method as the func unless the second argument happens to be an array or vector of pointers (or references) to instances of exactly the right class -- and of course LLSD can't store such at all. It's tempting to pass std::bind(std::mem_fn(ptr_to_method), instance), but that won't work: std::bind() requires a value or placeholder for each argument to pass to the bound function. The bind() expression above would only work for a nullary method. std::bind_front() would work, but that doesn't arrive until C++20. Again, once we get there we'll defer to the std:: implementation. Instead of the generic __cplusplus, check the appropriate feature-test macro for availability of each of std::invoke(), std::apply() and std::bind_front(). Change apply() error handling from assert() to new LL::apply_error exception. LLEventDispatcher must be able to intercept apply() errors. Move validation and synthesis of the relevant error message to new apply.cpp source file. Add to llptrto.h new LL::get_ref() and LL::get_ptr() template functions to unify the cases of a calling template accepting either a pointer or a reference. Wrapping the parameter in either get_ref() or get_ptr() allows dereferencing the parameter as desired. Move LL::apply(function, LLSD) argument validation/manipulation to a non- template function in llsdutil.cpp: no need to replicate that logic in the template for every CALLABLE specialization. The trouble with passing bind_front(std::mem_fn(ptr_to_method), instance) to apply() is that since bind_front() accepts and forwards variadic additional arguments, apply() can't infer the arity of the bound ptr_to_method. Address that by introducing apply_n<arity>(function, LLSD), permitting a caller to infer the arity of ptr_to_method and explicitly pass it to apply_n(). Polish up lleventdispatcher_test.cpp accordingly. Wrong LLSD type and wrong number of arguments now produce different (somewhat more informative) error messages. Moreover, passing too many entries in an LLSD array used to work: the extra arguments used to be ignored. Now we require that the size of the array match the arity of the target function. Change the too-many-arguments tests from success testing to error testing. Replace 'foreach' aka BOOST_FOREACH macro invocations with range 'for'. Replace STRINGIZE(item0 << item1 << ...) with stringize(item0, item1, ...). (cherry picked from commit 9c049563b5480bb7e8ed87d9313822595b479c3b)
2023-07-13DRTVWR-558: Extend LL::apply() to LLSD array arguments.Nat Goodspeed
Make apply(function, std::array) and apply(function, std::vector) available even when we borrow the C++17 implementation of apply(function, std::tuple). Add apply(function, LLSD) with interpretations: * isUndefined() is treated as an empty array, for calling a nullary function * scalar LLSD is treated as a single-entry array, for calling a unary function * isArray() converts function parameters using LLSDParam * isMap() is an error. Add unit tests for all flavors of LL::apply(). (cherry picked from commit 3006c24251c6259d00df9e0f4f66b8a617e6026d)
2023-07-12SL-18330: Merge commit '6b53036' into DRTVWR-587-maint-VNat Goodspeed
Bring over part of the LLEventDispatcher work inspired by DRTVWR-558.
2023-05-23SL-19744: Remove LLApp::startErrorThread() and references.Nat Goodspeed
2023-03-29Merge remote-tracking branch 'origin/main' into DRTVWR-559Brad Linden
2023-03-30Merge branch 'main' into DRTVWR-577-maint-SAndrey Lihatskiy
# Conflicts: # indra/cmake/CMakeLists.txt # indra/newview/skins/default/xui/es/floater_tools.xml
2023-01-31SL-19110 Fast hashing classes for use in place of the slow LLMD5, where ↵Henri Beauchamp
speed matters. (#64) This commit adds the HBXX64 and HBXX128 classes for use as a drop-in replacement for the slow LLMD5 hashing class, where speed matters and backward compatibility (with standard hashing algorithms) and/or cryptographic hashing qualities are not required. It also replaces LLMD5 with HBXX* in a few existing hot (well, ok, just "warm" for some) paths meeting the above requirements, while paving the way for future use cases, such as in the DRTVWR-559 and sibling branches where the slow LLMD5 is used (e.g. to hash materials and vertex buffer cache entries), and could be use such a (way) faster algorithm with very significant benefits and no negative impact. Here is the comment I added in indra/llcommon/hbxx.h: // HBXXH* classes are to be used where speed matters and cryptographic quality // is not required (no "one-way" guarantee, though they are likely not worst in // this respect than MD5 which got busted and is now considered too weak). The // xxHash code they are built upon is vectorized and about 50 times faster than // MD5. A 64 bits hash class is also provided for when 128 bits of entropy are // not needed. The hashes collision rate is similar to MD5's. // See https://github.com/Cyan4973/xxHash#readme for details.
2023-01-31SL-19110 Fast hashing classes for use in place of the slow LLMD5, where ↵Henri Beauchamp
speed matters. (#64) This commit adds the HBXX64 and HBXX128 classes for use as a drop-in replacement for the slow LLMD5 hashing class, where speed matters and backward compatibility (with standard hashing algorithms) and/or cryptographic hashing qualities are not required. It also replaces LLMD5 with HBXX* in a few existing hot (well, ok, just "warm" for some) paths meeting the above requirements, while paving the way for future use cases, such as in the DRTVWR-559 and sibling branches where the slow LLMD5 is used (e.g. to hash materials and vertex buffer cache entries), and could be use such a (way) faster algorithm with very significant benefits and no negative impact. Here is the comment I added in indra/llcommon/hbxx.h: // HBXXH* classes are to be used where speed matters and cryptographic quality // is not required (no "one-way" guarantee, though they are likely not worst in // this respect than MD5 which got busted and is now considered too weak). The // xxHash code they are built upon is vectorized and about 50 times faster than // MD5. A 64 bits hash class is also provided for when 128 bits of entropy are // not needed. The hashes collision rate is similar to MD5's. // See https://github.com/Cyan4973/xxHash#readme for details.
2022-12-12Merge remote-tracking branch 'origin/main' into DRTVWR-559Brad Linden
2022-12-12Merge branch 'main' into DRTVWR-568Callum Prentice
2022-12-09SL-18809: Add WorkSchedule; remove timestamps from WorkQueue.Nat Goodspeed
For work queues that don't need timestamped tasks, eliminate the overhead of a priority queue ordered by timestamp. Timestamped task support moves to WorkSchedule. WorkQueue is a simpler queue that just waits for work. Both WorkQueue and WorkSchedule can be accessed via new WorkQueueBase API. Of course the WorkQueueBase API doesn't deal with timestamps, but a WorkSchedule can be accessed directly to post timestamped tasks and then handled normally (e.g. by ThreadPool) to run them. Most ThreadPool functionality migrates to new ThreadPoolBase class, with template subclass ThreadPoolUsing<WorkQueue> or ThreadPoolUsing<WorkSchedule> depending on need. ThreadPool is now an alias for ThreadPoolUsing<WorkQueue>. Importantly, ThreadPoolUsing::getQueue() delivers a reference to the specific queue subclass type, so you can post timestamped tasks on a queue retrieved from ThreadPoolUsing<WorkSchedule>::getQueue(). Since ThreadPool is no longer a simple class but an alias for a particular template specialization, introduce threadpool_fwd.h to forward-declare it. Recast workqueue_test.cpp to exercise WorkSchedule, since some of the tests are time-based. A future todo would be to exercise each applicable test with both WorkQueue and WorkSchedule.
2022-12-09DRTVWR-559: Introduce LLInstanceTrackerSubclass mediator class.Nat Goodspeed
Deriving your tracked class T from LLInstanceTracker<T> gives you T::getInstance() et al. But what about a subclass S derived from T? S::getInstance() still delivers a pointer to T, requiring explicit downcast. And so on for other LLInstanceTracker methods. Instead, derive S from LLInstanceTrackerSubclass<S, T>. This implies that S is a grandchild class of T, but it also recasts the LLInstanceTracker methods to deliver results for S rather than for T.
2022-10-24Merge master into DRTVWR-568 (and fix conflicts)Callum Linden
2022-10-23Remove ll::bugsplat as a llcommon depencencyNicky
In theory it is fine to do that, in practice it does break gatekeeper in subtle ways due to https://developer.apple.com/library/archive/technotes/tn2206/_index.html#//apple_ref/doc/uid/DTS40007919-CH1-TNTAG207 Having bugsplat linked to all executables results in executables with an embedded rpath that is invalid for Gatekeeper. Luckily it shows this is in the worst possible way. The viewer cannot be started with a non helpful message of teh viewer being unable to verified. While at the same time spctl and codesign both show no errors at all.
2022-10-21Merge branch 'master' (DRTVWR-548) into DRTVWR-559Andrey Kleshchev
# Conflicts: # indra/llrender/llgl.cpp # indra/llrender/llrendertarget.cpp # indra/newview/VIEWER_VERSION.txt # indra/newview/app_settings/shaders/class1/deferred/materialF.glsl # indra/newview/llfloaterpreference.cpp # indra/newview/llviewercontrol.cpp # indra/newview/llviewermenu.cpp # indra/newview/llviewertexturelist.cpp # indra/newview/llvovolume.cpp
2022-10-20Merge branch 'master' into DRTVWR-565-maint-PAndrey Lihatskiy
2022-09-17SL-17238 Fix coding policy build issuesAndrey Kleshchev
2022-08-30Merge remote-tracking branch 'remotes/origin/DRTVWR-563' into DRTVWR-559Dave Parks
2022-07-30SL-17868 Crash at ThreadRecorder::bringUpToDateAndrey Kleshchev
According to bugsplat get_thread_recorder was null Replaced apr based LLThreadLocalPointer with thread_local
2022-06-29Merge branch 'master' into DRTVWR-548-maint-NAndrey Lihatskiy
# Conflicts: # doc/contributions.txt # indra/newview/llviewercontrol.cpp
2022-06-22SL-17634 Replace deprecated carbon Gestalt callsMaxim Nikolenko
2022-06-18DRTVWR-564: WIP: Add LazyEventAPI and tests. Tests don't yet pass.Nat Goodspeed
LazyEventAPI is a registrar that implicitly instantiates some particular LLEventAPI subclass on demand: that is, when LLEventPumps::obtain() tries to find an LLEventPump by the registered name. This leverages the new LLEventPumps::registerPumpFactory() machinery. Fix registerPumpFactory() to adapt the passed PumpFactory to accept TypeFactory parameters (two of which it ignores). Supplement it with unregisterPumpFactory() to support LazyEventAPI instances with lifespans shorter than the process -- which may be mostly test programs, but still a hole worth closing. Similarly, add unregisterTypeFactory(). A LazyEventAPI subclass takes over responsibility for specifying the LLEventAPI's name, desc, field, plus whatever add() calls will be needed to register the LLEventAPI's operations. This is so we can (later) enhance LLLeapListener to consult LazyEventAPI instances for not-yet-instantiated LLEventAPI metadata, as well as enumerating existing LLEventAPI instances. The trickiest part of this is capturing calls to the various LLEventDispatcher::add() overloads in such a way that, when the LLEventAPI subclass is eventually instantiated, we can replay them in the new instance. LLEventAPI acquires a new protected constructor specifically for use by a subclass registered by a companion LazyEventAPI. It accepts a const reference to LazyEventAPIParams, intended to be opaque to the LLEventAPI subclass; the subclass must declare a constructor that accepts and forwards the parameter block to the new LLEventAPI constructor. The implementation delegates to the existing LLEventAPI constructor, plus it runs deferred add() calls. LLDispatchListener now derives from LLEventStream instead of containing it as a data member. The reason is that if LLEventPumps::obtain() implicitly instantiates it, LLEventPumps's destructor will try to destroy it by deleting the LLEventPump*. If the LLEventPump returned by the factory function is a data member of an outer class, that won't work so well. But if LLDispatchListener (and by implication, LLEventAPI and any subclass) is derived from LLEventPump, then the virtual destructor will Do The Right Thing. Change LLDispatchListener to *not* allow tweaking the LLEventPump name. Since the overwhelming use case for LLDispatchListener is LLEventAPI, accepting but silently renaming an LLEventAPI subclass would ensure nobody could reach it. Change LLEventDispatcher's use of std::enable_if to control the set of add() overloads available for the intended use cases. Apparently this formulation is just as functional at the method declaration point, while avoiding the need to restate the whole enable_if expression at the method definition point. Add lazyeventapi_test.cpp to exercise.
2022-06-09SL-17483: Make it possible to override width of any ThreadPool.Nat Goodspeed
Introduce CommonControl, which in a running viewer (or any program containing an LLViewerControlListener instance) gives access to LLViewerControl functionality, e.g. getting, setting or enumerating control variables -- without introducing a link dependency on newview. Make ThreadPool's constructor consult CommonControl to check for an override for the width of the new ThreadPool in the Global (i.e. gSavedSettings) setting ThreadPoolSizes, and honor that if found. Introduce static ThreadPool methods getConfiguredWidth(), to query for such an override on any particular ThreadPool name; and getWidth(), to ask for the width of an instance if that instance already exists, else the width with which it *would* be instantiated.
2022-06-05Merge remote-tracking branch 'origin/DRTVWR-543-maint_cmake' into ↵Nicky
DRTVWR-543-maint_cmake
2022-05-27Merge branch 'master' into DRTVWR-543-maintAndrey Lihatskiy
# Conflicts: # autobuild.xml # indra/cmake/LLCommon.cmake # indra/llcommon/CMakeLists.txt # indra/llrender/llgl.cpp # indra/newview/llappviewer.cpp # indra/newview/llface.cpp # indra/newview/llflexibleobject.cpp # indra/newview/llvovolume.cpp
2022-05-07Adapt gnerator expression usage to work on OSX.Nicky
2022-05-01Remove setting of HEADER_FILE_ONLY on .h* files, cmake automaticallyNicky
sets the property on those.
2022-04-17Switch to target_include_directoriesNicky
All 3Ps include dirs are treated as SYSTEM, this will stop compilers stop emitting warnings from those files and greatly helps having high warning levels and not being swamped by warnings that come from external libraries.
2022-04-16Streamline bugsplat target:Nicky
- Fix usage of bugsplat::bugsplat by using ll::bugsplat - Use bugsplat define by importing target not by using hand crafted magic
2022-04-16Remove undefined variable GOOGLE_PERFTOOLS_LIBRARIESNicky
2022-04-16Create a new target ll::oslibrary to link against libs specific to the OS ↵Nicky
compiled on. This gets rid of the a few OS specific set and uses variables (which some even seemed mostly duplicate like WINDOWS_LIBRARIES ans UI_LIBRARIES) and it also solves the problem of having them to tack on every target, as of no they come as a transitive dependency from llcommon
2022-04-13Rework cmake, the original plan was to maybe be able to use conan targets ↵Nicky
with the same name (that's why 3ps had names like apr::apr), but it's safer and saner to put the LL 3ps under the ll:: prefix. This also allows means it is possible to get rid of that bad "if( TRAGET ...) return() endif()" pattern and rather use include_guard().
2022-04-06On OSX llcommon also needs CMAKE_CURRENT_SOURCE_DIR as PRIVATE include dir.Nicky
2022-04-06Move CMake files to modernized cmake syntax, step 1.Nicky
Change projects to cmake targetsto get rid of havig to hardcore include directories and link libraries in consumer projects.
2022-01-14SL-16606: Add categoriesPtolemy
2021-11-24DRTVWR-546, SL-16220, SL-16094: Undo previous glthread branch revert.Nat Goodspeed
Reverting a merge is sticky: it tells git you never want to see that branch again. Merging the DRTVWR-546 branch, which contained the revert, into the glthread branch undid much of the development work on that branch. To restore it we must revert the revert. This reverts commit 029b41c0419e975bbb28454538b46dc69ce5d2ba.
2021-11-19Merge branch 'master' into DRTVWR-543-maintAndrey Lihatskiy
# Conflicts: # indra/newview/llagentwearables.cpp # indra/newview/llvoicevivox.cpp
2021-11-16DRTVWR-546 merge in master v6.5.1Dave Houlton
2021-11-15Revert "SL-16220: Merge branch 'origin/DRTVWR-546' into glthread"Dave Houlton
This reverts commit 5188a26a8521251dda07ac0140bb129f28417e49, reversing changes made to 819088563e13f1d75e048311fbaf0df4a79b7e19.
2021-10-22SL-16220: Merge branch 'master' into sl-16220Nat Goodspeed
2021-10-22SL-16220: Add LL::ThreadPool class and a "General" instance.Nat Goodspeed
ThreadPool bundles a WorkQueue with the specified number of worker threads to service it. Each ThreadPool has a name that can be used to locate its WorkQueue. Each worker thread calls WorkQueue::runUntilClose(). ThreadPool listens on the "LLApp" LLEventPump for shutdown notification. On receiving that, it closes its WorkQueue and then join()s each of its worker threads for orderly shutdown. Add a settings.xml entry "ThreadPoolSizes", the first LLSD-valued settings entry to expect a map: pool name->size. The expectation is that usually code instantiating a particular ThreadPool will have a default size in mind, but it should check "ThreadPoolSizes" for a user override. Make idle_startup()'s STATE_SEED_CAP_GRANTED state instantiate a "General" ThreadPool. This is function-static for lazy initialization. Eliminate LLMainLoopRepeater, which is completely unreferenced. Any potential future use cases are better addressed by posting to the main loop's WorkQueue. Eliminate llappviewer.cpp's private LLDeferredTaskList class, which implemented LLAppViewer::addOnIdleCallback(). Make addOnIdleCallback() post work to the main loop's WorkQueue instead.
2021-10-14Merge branch 'master' into DRTVWR-545-maint-mixAndrey Lihatskiy
2021-10-07SL-16024: Merge branch 'DRTVWR-546' into SL-16024-to-546Nat Goodspeed
2021-10-07SL-16024: Add LL::WorkQueue for passing work items between threads.Nat Goodspeed
A typical WorkQueue has a string name, which can be used to find it to post work to it. "Work" is a nullary callable. WorkQueue is a multi-producer, multi-consumer thread-safe queue: multiple threads can service the WorkQueue, multiple threads can post work to it. Work can be scheduled in the future by submitting with a timestamp. In addition, a given work item can be scheduled to run on a recurring basis. A requesting thread servicing a WorkQueue of its own, such as the viewer's main thread, can submit work to another WorkQueue along with a callback to be passed the result (of arbitrary type) of the first work item. The callback is posted to the originating WorkQueue, permitting safe data exchange between participating threads. Methods are provided for different kinds of servicing threads. runUntilClose() is useful for a simple worker thread. runFor(duration) devotes no more than a specified time slice to that WorkQueue, e.g. for use by the main thread.