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CoWork

 

class CoWork

This class is indented as general parallelization tool. Whenever jobs (e.g. loop iterations) are independent (they do not share any data between iterations), CoWork can be used to relatively easily spawn loop iterations over threads and thus over CPU cores. Note that previous statement does not preclude CoWork iterations to share data at all - sharing data using Mutex or similar serialization mechanisms still works. CoWork works with fixed-size thread pool, which is created during initialization phase (which first CoWork constructor is called). No more thread are created or destroyed during normal work. Nesting of CoWork instances is also possible. Thread pool is normally terminated when the main thread finishes.

No synchronization is required to access CoWork instances from various threads (CoWork is internally synchronized).

Implementation notes: Current implementation has single global FIFO stack for 2048 scheduled jobs. When there is no slot available when scheduling the job, it is performed immediately by Do. Finish method has to wait until all jobs scheduled by CoWork instance are finished, while waiting it attempts to perform scheduled jobs from the same instance. That way work always progresses even if there is shortage of worker threads.

 

Public Method List

 

static bool TrySchedule(Function<void ()>&& fn)

static bool TrySchedule(const Function<void ()>& fn)

This is a low-level function that attempts to schedule fn to be executed by worker thread. Returns true if fn was scheduled, false if not (in case there is no slot left in scheduling stacks). Note that this function only schedules the function, the exact time of execution is unknown.

 


 

static void Schedule(Function<void ()>&& fn)

static void Schedule(const Function<void ()>& fn)

Similar to TrySchedule, but always schedules fn - even if it has to wait for slot to become available.

 


 

void Do(Function<void ()>&& fn)

void Do(const Function<void ()>& fn)

CoWork& operator&(const Function<void ()>& fn)

CoWork& operator&(Function<void ()>&& fn)

Schedules fn to be executed. All changes to data done before Do are visible in the scheduled code. The order of execution or whether the code is execute in another or calling thread is not specified. In certain situations (no scheduling slot available), Do can perform scheduled job immediately in calling thread.

 


 

static void FinLock()

This functions is to be called in scheduled routine. Its purpose is to serialize access to shared data at the end of the routine. The rationale is that CoWork has to lock some mutex anyway after scheduled code finishes, so FinLock can lock this mutex a bit earlier, joining two mutex locks into single one. Of course, as with all locks, execution of locked code should be short as not to cause congestion of CoWork scheduling.

 


 

void Finish()

Waits until all jobs scheduled using Do (or operator&) are finished. All changes to data performed by scheduled threads are visible after Finish. While waiting, Finish can perform scheduled jobs.

 


 

bool IsFinished()

Checkes whether all jobs scheduled using Do (or operator&) are finished. All changes to data performed by scheduled threads are visible after IsFinished returns true (so this is basically non-blocking variant of Finish).

 


 

~CoWork()

Calls Finish().

 


 

static bool IsWorker()

Returns true if current thread is CoWork worker thread.

 


 

static int GetWorkerIndex()

Returns the index of worker - index is >= 0 and < GetPoolSize(). This is useful if there is a need for per-thread resources.

 


 

static int GetPoolSize()

Returns the current count of worker threads.

 


 

static void SetPoolSize(int n)

Adjusts the thread pool size (default pool size is CPU_Cores() + 2).

 

 

CoWorkerResources

 

template <class T>

class CoWorkerResources

This is a simple helper class that provides per-worker resources. For example, certain calculation requires the instance of computation model that is not immutable, but can be reused over iterations. In single-thread code, a single instance of such model would be used over the whole loop, however in multi-threaded code, each worker thread, plus thread that created CoWork need its own instance. CoWorkerResources helps to manage such situation.

 

Public Method List

 

CoWorkerResources()

Creates a required number of instances so that each sub-job of CoWork has its unique instance.

 


 

CoWorkerResources(Event<T&initializer)

Creates a required number of instances so that each sub-job of CoWork has its unique instance.and initializes them using initializer.

 


 

int GetCount() const

Returns the number of instances. Note that this is equal to CoWork::GetPoolSize() if thread that created CoWorkerResources is itself CoWork worker, or CoWork::GetPoolSize() + 1 if it is any other thread. The reason for this is that CoWork owner can execute CoWork jobs too (while waiting in Finish).

 


 

T& operator[](int i)

Returns instance i. Together with GetCount can be used to initialize resources (alternative method to using constructor with initializer.

 


 

T& Get()

T& operator~()

Supposed to be called in CoWork job, returns a reference to resources unique for the thread.

 


 

T *begin()

T *end()

Standard iterator access.

 

 

Last edit by cxl on 12/05/2016. Do you want to contribute?. T++