c# - (Sometimes) The given key was not present in the dictionary -

i using code below start threads list parameter throws exception:

the given key not present in dictionary

from line:

thread movethread = new thread(() => movetask(controllerdictionary[i])); 

how can fix error?

full code:

var controllerdictionary = configfile.controllerlist.select((c, i) => new { controller = c, index = })     .groupby(x => x.index % appsettings.simultaneousprocessnumber)     .select((g, i) => new { groupindex = i, group = g })     .todictionary(x => x.groupindex, x => x.group.select(xx => xx.controller).tolist());  (int = 0; < controllerdictionary.count; i++) {      thread movethread = new thread(() => movetask(controllerdictionary[i]));      movethread.start();       foreach (var controller in controllerdictionary[i])          logger.write(string.format("{0} in move thread {1}.", controller.ip, (i + 1)),eventlogentrytype.information, appsettings.loginfomessages); } 

you're capturing variable i, rather value. have several threads calling movetask using same index... , value of i equal controllerdictionary.count.

if take copy of i variable within loop, fixes problem you'll separate variable on each iteration of loop:

for (int = 0; < controllerdictionary.count; i++) {     int index = i;     thread movethread = new thread(() => movetask(controllerdictionary[index]));     ...  } 

or better, extract controllerdictionary fetch thread entirely:

for (int = 0; < controllerdictionary.count; i++) {     var value = controllerdictionary[i];     thread movethread = new thread(() => movetask(value));     ...  } 

additionally, it's not clear why you're using dictionary @ all. given know keys in range [0, count) why don't use array? you'd change query to:

var controllerlists = configfile.controllerlist     .select((c, i) => new { controller = c, index = })     .groupby(x => x.index % appsettings.simultaneousprocessnumber)     .select(g => g.select(xx => xx.controller).tolist())     .toarray();