c# - How do I prevent the creation of multiple background processes working on the same request? -

i have simple webapi controller method that's purpose trigger background processing , return 202 accepted response (without having completed background processing consistent 202 response.)

public async task<ihttpactionresult> dosomething(string id) {     hostingenvironment.queuebackgroundworkitem(async ct =>     {         //do work     }     return responsemessage(new httpresponsemessage(httpstatuscode.accepted)); } 

however, want able prevent multiple requests same endpoint same id triggering multiple instances of same background processing simultaneously.

effectively, if 2 requests same id's made @ same time (or near enough), first 1 processing id , second 1 able identify , take action accordingly , not duplicate work that's being done.

i'd avoid databases/persistent storage if @ possible , i'm aware of risks of running async tasks within iis worker process - sake of argument, background processing not critical.

how can go doing this? appreciated.

you'll need kind of storage shared between possible workers. be, example:

• a static variable. easiest implement, has limitations when application not run in 1 appdomain (especially important if want scale). not best way
• an sql database: common one. if application uses one, i'd go route.
• a no-sql database, example key-value store. might alternative if application not use sql database yet.
• some external component such workflow management tool

edit: example using concurrentdictionary (per request of thread starter - stil think using (possibly nosql) database elegant way) - put tasks dictionary:

private concurrentdictionary<string, task<sometype>> _cache = new //...  var task = _cache.getoradd("<key>", key => task.run(() => /*do work*/)); if (task.iscompleted)    /*result ready*/; else    /*have wait*/;