Feature #811

LocalProcess & AProcess should have "WaitForExit" synchronization method

Added by Zbigniew Rebacz over 7 years ago. Updated over 7 years ago.

Status:RejectedStart date:07/19/2014
Priority:NormalDue date:
Assignee:Zbigniew Rebacz% Done:

0%

Category:CoreSpent time:-
Target version:-

Description

I think it will be nice if LocalProcess & AProcess will posses one very usful method. It is "void WaitForExit()" method. The main goal of it is to wait until the process is finished.

Implementation:

void LocalProcess::WaitForExit()
{
    if(!IsRunning())
        return;

    bool isSuccess = false;
#ifdef PLATFORM_POSIX
    int status;
    if(waitpid(pid, &status, 0) == pid) {
        isSuccess = true;
        pid = 0;
    }
#endif
#ifdef PLATFORM_WIN32
    if(WaitForSingleObject(hProcess, INFINITE)) {
        isSuccess = true;
        hProcess = NULL;
    }
#endif
    if(isSuccess)
        CloseInputAndOutput();
}

Of course this patch also intoduce new private method "CloseInputAndOutput" which target is to close all pipes related to LocalProcess. (All implementation is included in source files).

Test case (I tested this solution with valgrind to make sure that we don't have any memory leaks):

#include <Core/Core.h>

using namespace Upp;

void startApp(LocalProcess& process) {
    #ifdef PLATFORM_POSIX
        process.Start("/usr/bin/xterm");
    #endif
    #ifdef PLATFORM_WIN32
        process.Start("E:\\Programy\\Notepad++\\notepad++.exe");
    #endif
}

CONSOLE_APP_MAIN {
    for (int i = 0; i < 1; i++) {
        // Test if "WaitForExit" works.
        LocalProcess myProcess;
        startApp(myProcess);
        myProcess.WaitForExit();

        // Test if we can reuse the same instance of LocalProcces for new task.
        startApp(myProcess);
        myProcess.WaitForExit();
    }
}

LocalProcess.cpp Magnifier (12.6 KB) Zbigniew Rebacz, 07/19/2014 01:27 PM

LocalProcess.h Magnifier (2.68 KB) Zbigniew Rebacz, 07/19/2014 01:27 PM

Process.cpp Magnifier - Test case (561 Bytes) Zbigniew Rebacz, 07/19/2014 01:27 PM

History

#1 Updated by Zbigniew Rebacz over 7 years ago

We can also expand "WaitForExit" method by timeout variable.

#2 Updated by Miroslav Fidler over 7 years ago

  • Status changed from Patch ready to New
  • Assignee changed from Miroslav Fidler to Zbigniew Rebacz

This has a problem: if slave process produces a lot of output, it will block forever (pipe buffer will get full as we are not reading it, process will be blocked).

#3 Updated by Zbigniew Rebacz over 7 years ago

  • Assignee changed from Zbigniew Rebacz to Miroslav Fidler

Should we close pipes befor we start waiting and throw exception if whole operation fails?

LocalProcess localProcess("/usr/bin/xterm");
try {
    localProcess.Wait();
}
catch(const EnviromentException& e) {
    // Pipes are not available...
    Cout() << e.what() << "\n";
    localProcess.Kill();
}

Or, we can just do this inside WaitForExit method. But, in above case client programer can decide what to do in exceptional situation. What do you think about this solution?

P.S.
It will be good if we will possess a set of exceptions for different situations.

#4 Updated by Zbigniew Rebacz over 7 years ago

  • Status changed from New to Rejected
  • Assignee changed from Miroslav Fidler to Zbigniew Rebacz

#5 Updated by Zbigniew Rebacz over 7 years ago

It seems that it is bad idea, because to make it works perfect we will need more changes in Core.

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