Using TParallel.For from the Parallel Programming Library
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The Parallel Programming Library (PPL) includes a loop function, TParallel.For, that allows to run its loops in parallel.
Within parallel loops, you must transform your operations into thread-safe operations. You can use members of the System.SyncObjs unit, such as TInterlocked methods.
Converting a For Loop into a TParallel.For Loop
Delphi:
| For Loop | TParallel.For Loop |
|---|---|
for I := 1 to 10 do
begin
// …
end;
|
TParallel.For(1, 10, procedure(I: Integer)
begin
// …
end);
|
C++:
If you are using a Clang-enhanced C++ compiler, you can use lambda expressions:
| For Loop | TParallel.For Loop |
|---|---|
for (int i = 1; i <= 10; i++) {
// …
}
|
TParallel::For(0, 10, TProc1<int>([](int I){
// …
}));
|
You can alternatively use a functor, which works with both previous-generation compilers and Clang-enhanced compilers:
| For Loop | TParallel.For Loop |
|---|---|
for (int i = 1; i <= 10; i++) {
// (Loop logic)
}
|
class TMyFunctor : public TCppInterfacedObject<TProc__1<int> > {
public:
void __fastcall Invoke(int I) {
// (Loop logic)
}
};
// …
TParallel::For(1, 10, System::DelphiInterface<TProc__1<int> >(new TMyFunctor()));
|
If the loop needs access to one or more variables from the context outside the callback function, you must use a functor as follows:
- Declare variables in the functor class to hold copies or references to the variables that you need.
- Declare a constructor of the functor class that accepts the copies or references to those variables as parameters and initializes the corresponding functor variables with their values.
- Pass those variables to the contructor when you instantiate the functor.
- In your logic, in
Invoke(), you can access those functor variables.
For example:
class TMyFunctor : public TCppInterfacedObject<TProc__1<int> > {
public:
TMyFunctor(int a, TB *b) : a(a), b(b) {}
void __fastcall Invoke(int I) {
// (Loop logic)
}
int a;
TB *b;
};
// …
TParallel::For(1, 10, System::DelphiInterface<TProc__1<int> >(new TMyFunctor(a, b)));