c# - How to substitute synchronization context / task scheduler to another one inside TaskCompletionSource.Task for ConfigureAwait(false)? -

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• how can prevent synchronous continuations on task? 6 answers

assume created library containing such method:

task mylibrarymethodasync() {     var taskcompletionsource = new taskcompletionsource<object>();      action myworkitem =         () =>         {             // simulate work.             // actual work items depend on input params.             thread.sleep(timespan.fromseconds(1));              taskcompletionsource.setresult(null);         };      // next 2 lines simplification demonstration.     // not have access workerthread - created     // , managed me lib.     // can - post short work items it.     var workerthread = new thread(new threadstart(myworkitem));     workerthread.start();      return taskcompletionsource.task; } 

any user of lib can call mylibrarymethodasync this

await mylibrarymethodasync().configureawait(false); verylongrunningmethod(); 

void verylongrunningmethod() {     thread.sleep(timespan.fromhours(1)); } 

and here problem comes – verylongrunningmethod executed inside taskcompletionsource.setresult(null) call , block workerthread long period of time, not desired behavior because workerthread intended run small portions of code (work items).

how substitute context / scheduler thread pool inside returned task making await x.configureawait(false) continue on thread pool, not on workerthread?

the current solution found is

task mylibrarymethodasync() {     // ...      return taskcompletionsource.task         .continuewith(x => x.result, taskscheduler.default); } 

however, not due overhead creates. may more elegant solution exists?

as of .net 4.6 there option in taskcreationoptions called runcontinuationsasynchronously, want, ensures continuations run asynchronously, rather run synchronously when setting result. taskcompletionsource has optional taskcreationoption parameter in constructor provide option.

if you're using earlier version of .net you'll need less efficient hack, such adding continuation, showed, or explicitly setting result in thread pool thread, rather through callback action.