c# - Where do these 1k threads come from -

i trying create application multi threaded downloads images website, introduction threading. (never used threading before)

but seems create 1000+ threads , not sure coming from.

i first queue thread thread pool, starters have 1 job in jobs array

foreach (job j in jobs) {     threadpool.queueuserworkitem(download, j); } 

which starts void download(object obj) on new thread loops through amount of pages (images needed / 42 images per page)

for (var = 0; < pages; i++) {     var downloadlink = new system.uri("http://www." + j.provider.tostring() + "/index.php?page=post&s=list&tags=" + j.tags + "&pid=" + * 42);      using (var wc = new webclient())     {         try         {             wc.downloadstringasync(downloadlink);             wc.downloadstringcompleted += (sender, e) =>             {                 response = e.result;                   processpage(response, false, j);             };         }         catch (system.exception e)         {             // unity editor equivalent of console.writeline             debug.log(e);         }     } } 

correct me if wrong, next void gets called on same thread

void processpage(string response, bool secondpass, job j) {     var wc = new webclient();     linkitem[] linkresponse = linkfinder.find(response).toarray();      foreach (linkitem in linkresponse)     {         if (secondpass)         {             if (string.isnullorempty(i.href))                 continue;             else if (i.href.contains("http://loreipsum."))             {                 if (downloadimage(i.href, id(i.href)))                     j.downloaded++;             }         }         else         {             if (i.href.contains(";id="))             {                 var alterresponse = wc.downloadstring("http://www." + j.provider.tostring() + "/index.php?page=post&s=view&id=" + id(i.href));                 processpage(alterresponse, true, j);             }         }     } } 

and passes on last function , downloads actual image

bool downloadimage(string target, int id) {     var url = new system.uri(target);     var fi = new system.io.fileinfo(url.absolutepath);     var ext = fi.extension;      if (!string.isnullorempty(ext))     {         using (var wc = new webclient())         {             try             {                 wc.downloadfileasync(url, id + ext);                 return true;             }             catch(system.exception e)             {                 if (debug) debug.log(e);             }         }     }     else     {         debug.log("returned without extension: " + url + " || " + fi.fullname);         return false;     }     return true; } 

i not sure how starting many threads, love know.

edit

the goal of program download different job in jobs @ same time (max of 5) each downloading maximum of 42 images @ time.

so maximum of 210 images can/should downloaded maximum @ times.

first of all, how did measure thread count? why think have thousand of them in application? using threadpool, don't create them yourself, , threadpool wouldn't create such great amount of them it's needs.

second, mixing synchronious , asynchronious operations in code. can't use tpl , async/await, let's go through code , count unit-of-works creating, can minimize them. after this, number of queued items in threadpool decrease , application gain performance need.

1. you don't set setmaxthreads method in application, so, according msdn:

   maximum number of thread pool threads
   number of operations can queued thread pool limited available memory; however, thread pool limits number of threads can active in process simultaneously. by default, limit 25 worker threads per cpu , 1,000 i/o completion threads.

   so must set maximum 5.

2. i can't find place in code check 42 images per job, incrementing value in processpage method.

3. check managedthreadid handle of webclient.downloadstringcompleted - execute in different thread or not.

4. you adding new item in threadpool queue, why using asynchronious operation downloading? use synchronious overload, this:

   processpage(wc.downloadstring(downloadlink), false, j); 

   this not create 1 item in threadpool queue, , wouldn't have sinchronisation context switch here.

5. in processpage wc variable doesn't being garbage collected, aren't freeing resourses here. add using statement here:

   void processpage(string response, bool secondpass, job j) {     using (var wc = new webclient())     {         linkitem[] linkresponse = linkfinder.find(response).toarray();          foreach (linkitem in linkresponse)         {             if (secondpass)             {                 if (string.isnullorempty(i.href))                     continue;                 else if (i.href.contains("http://loreipsum."))                 {                     if (downloadimage(i.href, id(i.href)))                         j.downloaded++;                 }             }             else             {                 if (i.href.contains(";id="))                 {                     var alterresponse = wc.downloadstring("http://www." + j.provider.tostring() + "/index.php?page=post&s=view&id=" + id(i.href));                     processpage(alterresponse, true, j);                 }             }         }     } } 

6. in downloadimage method use asynchronious load. adds item in threadpoll queue, , think can avoid this, , use synchronious overload too:

   wc.downloadfile(url, id + ext); return true;  

so, in general, avoid context-switching operations , dispose resources properly.