c++ - How can I use something like std::vector<std::mutex>? -

i have large, potentially varying, number of objects concurrently written into. want protect access mutexes. end, thought use std::vector<std::mutex>, doesn't work, since std::mutex has no copy or move constructor, while std::vector::resize() requires that.

what recommended solution conundrum?

edit: c++ random-access containers require copy or move constructors re-sizing? std::deque help?

edit again

first, thoughts. i'm not interested in solutions avoid mutices and/or move them objects (i refrain giving details/reasons). given problem want adjustable number of mutices (where adjustment guaranteed occur when no mutex locked), there appear several solutions.

1 use fixed number of mutices , use hash-function map objects mutices (as in captain oblivous's answer). result in collisions, number of collisions should small if number of mutices larger number of threads, still smaller number of objects.

2 define wrapper class (as in comicsansms's answer), e.g.

struct mutex_wrapper : std::mutex {   mutex_wrapper() = default;   mutex_wrapper(mutex_wrapper const&) noexcept : std::mutex() {}   bool operator==(mutex_wrapper const&other) noexcept { return this==&other; } }; 

and use std::vector<mutex_wrapper>.

3 use std::unique_ptr<std::mutex> manage individual mutexes (as in matthias's answer). problem approach each mutex individually allocated , de-allocated on heap. therefore, prefer

4 std::unique_ptr<std::mutex[]> mutices( new std::mutex[n_mutex] );

when number n_mutex of mutices allocated initially. should number later found insufficient, simply

if(need_mutex > n_mutex) {   mutices.reset( new std::mutex[need_mutex] );   n_mutex = need_mutex; } 

so of these (1,2,4) should use?

vector requires values movable, in order maintain contiguous array of values grows. create vector containing mutexes, couldn't might need resize it.

other containers don't have requirement; either deque or [forward_]list should work, long construct mutexes in place either during construction, or using emplace() or resize(). functions such insert() , push_back() not work.

alternatively, add level of indirection , store unique_ptr; comment in answer indicates believe cost of dynamic allocation unacceptable.