[aaron99]

Hello,

I'm very new to OpenFoam but at this time I work with an older version of it (2.3), I'm sure though it won't affect my question.

I would like to lock the fvSolution file because I have another process (created in python) which is writing to it causing it to be modified and then
reread by OpenFoam again.(their access is not synchronized and I want to synchronize it)

my ugly solution is to check explicitly when fvSolution is read:
In regIOobjectRead.C to override

bool Foam::regIOobject::read()
void Foam::regIOobject::close()

bool Foam::regIOobject::read() {
   if objPath == "fvSolution" {
     // lock the file to prevent it from being opened by other processes
     flock(fvSolution, LOCK_EX);
   ...
  }
}

 
void Foam::regIOobject::close() {
  ...
  flock(fvSolution, LOCK_UN); //unlock
}

preferred solution:
fvSolution.H also inherits from regIOobject.C so I could override

bool Foam::regIOobject::read() {//put lock and then call regIOobject::read()}
void Foam::regIOobject::close() {//release lock}

but these don't even get called, I ran the laplacian basic tutorial and
I received no output from these 2 methods. (is fvSolution.H used at all ?)

So how can I prevent an external process from writing to fvSolution when it's being read ?
I don't understand why changing fvSolution.H produces no output.

[alexeym]

Hi,

It is not quite clear what you want to achieve.
- Prohibit modification of fvSolution file?
- Ignore modifications of fvSolution file made by another process?

[aaron99]

Hello Alexey,


when fvSolution file is being read by OpenFoam(call it p1), I want to put a lock on it, such that other external process (call it p2) can't open the file (nor to read or write to it), that is p2 must wait for p1 to finish its job(aka close the stream) and only then p2 will proceed to do with fvSolution whatever p2 intends to.

With other words I want to give p1 exclusive rights to the file, so other processes will wait on p1 to finish its reading/writing and only then will other processes proceed to the fvSolution file.

Thank you!

[alexeym]

Hi,

Could you elaborate on how you have overridden read method in fvSolution class? For example, I have done the following:

1. Added to fvSolution.H

        virtual bool read();

just after constructor.

2. Created fvSolution.C with the following code:

#include "fvSolution.H"

bool Foam::fvSolution::read() {
    Info << "Enter fvSolution::read()" << endl;
    solution::read();
    Info << "Exit fvSolution::read()" << endl;
    return true;
}

3. Added fvSolution.C to Make/files in finiteVolume folder.

4. Recompiled OpenFOAM.

Started simulation, modified fvSolution file and saw:

...
DILUPBiCGStab:  Solving for k, Initial residual = 4.31815290661e-05, Final residual = 1.53001780603e-13, No Iterations 1
ExecutionTime = 58.26 s  ClockTime = 59 s

regIOobject::readIfModified() : 
    Re-reading object fvSolution from file ".../system/fvSolution"
Enter fvSolution::read()
Exit fvSolution::read()
fieldAverage averages write:
    Calculating averages

Courant Number mean: 0.00120237595803 max: 0.00120238118572
deltaT = 1.72796544044e-06
Time = 4.36792704089e-06

PIMPLE: Iteration 1
DILUPBiCGStab:  Solving for Ux, Initial residual = 0.00128745430922, Final residual = 6.81778088848e-12, No Iterations 1
...

Instead of useless printing you can put there locking and unlocking calls.

Though, I tested it on OpenFOAM-6 (compilation of 2.3.x with gcc-8 is rather unpleasant experience).

[aaron99]

Thanks for the repply.

the code you provided works fine but only in the case if fvSolution was modified, this triggers
the Foam::fvSolution::read() method which you overrode. (it is fine for the purpose)

But I thought that Foam::fvSolution::read() would be called also for the first time when fvSolution is read, but it's not.

So I would prefer to put a lock as well when fvSolution file is being read for the first time, can I achieve that without checking explicitly in regIOobjectRead.C ?

[alexeym]

Hi,

During construction of fvSolution class solution::read method is called (from solution constructor). So, you can either modify constructor of solution class (so it locks file), or you can try to modify fvSolution.

In case of solution class modification, you can add bool parameter to constructor with default false value. In fvSolution constructor you set this parameter to true. Locking/unlocking should be added to solution's read method.

In case of fvSolution modification, it is a little bit more complicated. Currently fvSolution is a child of the above mentioned solution, make it a child of fileLocker and solution. fileLocker is a class, which locks a file. To the fileLocker constructor you pass objectRegistry and file name, object constructs full path and lock the file. unlock method of fileLocker releases lock, created during construction.

So, after the modification, constructor of fvSolution will look like:

        fvSolution(const objectRegistry& obr)
        :
            fileLocker(obr, "fvSolution"),
            solution(obr, "fvSolution")
        {
            unlock();
        }