SemaphoreWrapper/src/ProcessSemaphore_C4droid.cpp

#if (defined(_C4DROID_)&&!defined(_TRY_POSIX)) /// Generic Version

#include "SemaphoreWrapper.h"
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/file.h>
#include <fcntl.h>
#include <string.h>
#include <unistd.h>
#include <stdio.h>
#include <error.h>
#include <stdlib.h>

#include <vector>
using namespace std;

class ProcessSemaphore::impl
{
public:
    char buff[256];
    int fd;

    int status;
    bool owner;

    struct LockInfo
    {
    public:
        int total_value;
        int current_value;
        vector<int> waiting;

        LockInfo()
        {
            total_value=0;
            current_value=0;
        }

        void writeTo(int fd) const
        {
            lseek(fd,0L,SEEK_SET);

            write(fd,&total_value,sizeof(int));
            write(fd,&current_value,sizeof(int));

            int num_waiting=waiting.size();
            write(fd,&num_waiting,sizeof(int));
            for(int i=0;i<num_waiting;i++)
            {
                write(fd,&waiting[i],sizeof(int));
            }
        }

        static LockInfo getFrom(int fd)
        {
            lseek(fd,0L,SEEK_SET);

            LockInfo x;
            read(fd,&x.total_value,sizeof(int));
            read(fd,&x.current_value,sizeof(int));

            int num_waiting=x.waiting.size();
            read(fd,&num_waiting,sizeof(int));
            for(int i=0;i<num_waiting;i++)
            {
                int n;
                read(fd,&n,sizeof(int));
                x.waiting.push_back(n);
            }
            return x;
        }
    };
};

ProcessSemaphore::ProcessSemaphore(int key, int action, int default_value) : _p(new impl)
{
    if(_p)
    {
        _p->status=0;
        _p->owner=false;

        memset(_p->buff,0,256);
        sprintf(_p->buff,"LibSemaphoreWrapper_%d",key);

        if(action==1)
        {
            _p->fd=open(_p->buff,O_RDWR|O_CREAT|O_EXCL,0666);
            _p->owner=true;
        }
        else
        {
            _p->fd=open(_p->buff,O_RDWR,0666);
        }

        if(_p->fd>=0) /// Opened.
        {
            _p->status=2;

            if(_p->owner)
            {
                flock(_p->fd,LOCK_EX);
                impl::LockInfo x;
                x.total_value=default_value;
                x.current_value=default_value;
                x.writeTo(_p->fd);
                flock(_p->fd,LOCK_UN);
            }
        }
        else
        {
            perror("Failed to open file. ");
        }

        if(_p->status!=0&&_p->status!=2) /// Clean up
        {
            close(_p->fd);
            _p->status=0;
        }
    }
}

ProcessSemaphore::~ProcessSemaphore()
{
    if(_p)
    {
        if(_p->status==2)
        {
            if(_p->owner)
            {
                /// Unlink it (delete on close) : Only owner will delete this file.
                unlink(_p->buff);
            }

            /// Close on delete.
            close(_p->fd);
        }

        delete _p;
    }
}

bool ProcessSemaphore::isReady() const
{
    return _p&&_p->status==2;
}

int ProcessSemaphore::p()
{
    flock(_p->fd,LOCK_EX);
    impl::LockInfo x=impl::LockInfo::getFrom(_p->fd);
    if(x.current_value<=0)
    {
        int thisPid=getpid();
        x.waiting.push_back(thisPid);
        x.writeTo(_p->fd);

        /*
        /// wait for signal...
        typedef void (*fnvi)(int);
        _global_process_semaphore_value=0;
        fnvi old=signal(SIGUSR1,_global_process_semaphore_handler);
        */

        flock(_p->fd,LOCK_UN);

        /// Sleep For 1 Second.
        sleep(1);

        while(1)
        {
            flock(_p->fd,LOCK_EX);
            x=impl::LockInfo::getFrom(_p->fd);
            if(x.current_value>0) /// Someone has released resource!
            {
                x.current_value=x.current_value-1;
                int sz=x.waiting.size();
                for(int i=0;i<sz;i++)
                {
                    if(x.waiting[i]==thisPid)
                    {
                        x.waiting.erase(x.waiting.begin()+i);
                        break;
                    }
                }

                x.writeTo(_p->fd);
                /// Pass!
                flock(_p->fd,LOCK_UN);
                break;
            }
            else /// Nothing happened...
            {
                flock(_p->fd,LOCK_UN);

                /// Sleep for 1 second.
                sleep(1);
            }
        }

        return 0;
    }
    else
    {
        x.current_value=x.current_value-1;
        x.writeTo(_p->fd);
        flock(_p->fd,LOCK_UN);

        /// Pass Operation P.
        return 0;
    }
}

int ProcessSemaphore::v()
{
    flock(_p->fd,LOCK_EX);
    impl::LockInfo x=impl::LockInfo::getFrom(_p->fd);
    x.current_value=x.current_value+1;
    x.writeTo(_p->fd);
    flock(_p->fd,LOCK_UN);
    return 0;
}

int ProcessSemaphore::wait()
{
    return p();
}

int ProcessSemaphore::notify()
{
    return v();
}



#endif /// End of try generic