C Windows winapi + multi-threading (HANDLE)_beginthreadex fail
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  1. #1
    Join Date
    Jan 2013
    Posts
    5

    C Windows winapi + multi-threading (HANDLE)_beginthreadex fail

    This code ruined all my day. Basically I have a list of 50 webservers I administrate, I want to check them if up/alive (isAlive() function), I parse my webservers.txt file with the 50 ips/hostnames and for fastness I try to use threads (10, 20 or 30 doesn't matter) then my compiled code seems only duplicate threads with the last line in my file.

    Code:
    #include <windows.h>
    #include <stdio.h>
    #include <string.h>
    #include <winsock.h>
    #include <process.h>
    #include <string.h>
    
    #pragma comment(lib, "wsock32.lib")
    
    unsigned int _stdcall isAlive(void *ptr)
    {
      struct sockaddr_in blah;
      struct hostent *he;
      WSADATA wsaData;
      int i;
      WORD wVersionRequested;
      SOCKET sock;
      char* addr = (char*)ptr;
    
      char buff[1024];
      char *ex;
      ex="GET /alive.php HTTP/1.0\n\n";
      char *fmsg="ALIVE";
    
      wVersionRequested = MAKEWORD(1, 1);
      if (WSAStartup(wVersionRequested , &wsaData)){
        printf("Winsock Initialization failed.\n");
        return(1);
      }
    
      if ((sock=socket(AF_INET,SOCK_STREAM,0))==INVALID_SOCKET){
        printf("Can not create socket.\n");
        return(1);
      }
      sock = socket(AF_INET,SOCK_STREAM,0);
      blah.sin_family = AF_INET;
      blah.sin_port = htons(80);
      blah.sin_addr.s_addr = inet_addr(addr);
    
      if ((he=gethostbyname(addr))!=NULL){
        memcpy((char *)&blah.sin_addr.s_addr,he->h_addr,he->h_length);
      }
      else{
        if((blah.sin_addr.s_addr=inet_addr(addr))==-1){
          WSACleanup();
          return(1);
        }
      }
    
      if (connect(sock,(struct sockaddr*)&blah,sizeof(blah))==0){
        send(sock,ex,strlen(ex),0);
        recv(sock,buff,sizeof(buff),0);
        if(strstr(buff,fmsg)!=NULL){
          printf("ALIVE: %s\n", addr);
        }
      }
    
      closesocket(sock);
      WSACleanup();
      _endthreadex(0);
      return(1);
    }
    
    int main(int argc,char *argv[])
    {
      if(argc!=2){
        printf("Usage: %s <webservers list>\n", argv[0]);
        return(1);
      }
    
      char *inname = argv[1];
      FILE *infile;
      char line_buffer[BUFSIZ];
      char line_number;
    
      infile = fopen(inname, "r");
      if (!infile) {
        printf("Couldn't open file %s for reading.\n", inname);
        return 0;
      }
    
      line_number = 0;
      HANDLE hThreadArray[200];
      while (fgets(line_buffer, sizeof(line_buffer), infile)) {
        unsigned threadID;
    	hThreadArray[line_number] = (HANDLE)_beginthreadex(0, 0, isAlive, line_buffer, 0, &threadID);
        ++line_number;
      }
      WaitForMultipleObjects(line_number, hThreadArray, TRUE, INFINITE);
      fclose(infile);
      return 0;
    }
    hosts.txt (11 lines in it)

    myhost.com
    mysecondhost.com
    ...
    mylasthost.com
    result:
    C:\Documents and Settings\Xtmtrx\Desktop\Code>checkalive.exe hosts.txt
    ALIVE: mylasthost.com
    ALIVE: mylasthost.com
    ALIVE: mylasthost.com
    ALIVE: mylasthost.com
    ALIVE: mylasthost.com
    ALIVE: mylasthost.com
    ALIVE: mylasthost.com
    ALIVE: mylasthost.com
    ALIVE: mylasthost.com
    ALIVE: mylasthost.com
    ALIVE: mylasthost.com

  2. #2
    Join Date
    Jul 2005
    Location
    Netherlands
    Posts
    2,012

    Re: C Windows winapi + multi-threading (HANDLE)_beginthreadex fail

    Quote Originally Posted by exitthematrix View Post
    Code:
      char line_buffer[BUFSIZ];
      char line_number;
    
      /* ... */
    
      line_number = 0;
      HANDLE hThreadArray[200];
      while (fgets(line_buffer, sizeof(line_buffer), infile)) {
        unsigned threadID;
    	hThreadArray[line_number] = (HANDLE)_beginthreadex(0, 0, isAlive, line_buffer, 0, &threadID);
        ++line_number;
      }
      WaitForMultipleObjects(line_number, hThreadArray, TRUE, INFINITE);
      fclose(infile);
      return 0;
    }
    You are passing a pointer to the 'line_buffer' to each thread. However, you don't know when that thread will start. You may well have overwritten the contents of the buffer with the next line before the thread starts.
    Cheers, D Drmmr

    Please put [code][/code] tags around your code to preserve indentation and make it more readable.

    As long as man ascribes to himself what is merely a posibility, he will not work for the attainment of it. - P. D. Ouspensky

  3. #3
    Join Date
    Jan 2013
    Posts
    5

    Re: C Windows winapi + multi-threading (HANDLE)_beginthreadex fail

    An how should I safely start every thread with different lines read from my file? Because if I just do "printf("%s", line_buffer)" that works.

  4. #4
    Join Date
    Jul 2005
    Location
    Netherlands
    Posts
    2,012

    Re: C Windows winapi + multi-threading (HANDLE)_beginthreadex fail

    Quote Originally Posted by exitthematrix View Post
    An how should I safely start every thread with different lines read from my file? Because if I just do "printf("%s", line_buffer)" that works.
    What do you mean with "that works"? Doing a single run and looking at the results does not tell you much in a multi-threaded world.

    You should use a different buffer for each thread. That way you don't need to perform any synchronization. Seems the easiest for the use case you described.
    Cheers, D Drmmr

    Please put [code][/code] tags around your code to preserve indentation and make it more readable.

    As long as man ascribes to himself what is merely a posibility, he will not work for the attainment of it. - P. D. Ouspensky

  5. #5
    Join Date
    Jan 2013
    Posts
    5

    Re: C Windows winapi + multi-threading (HANDLE)_beginthreadex fail

    Quote Originally Posted by D_Drmmr View Post
    What do you mean with "that works"? Doing a single run and looking at the results does not tell you much in a multi-threaded world.

    You should use a different buffer for each thread. That way you don't need to perform any synchronization. Seems the easiest for the use case you described.
    By "that works" I mean using "printf("%s", line_buffer)" that prints out every line out from my text.

  6. #6
    Join Date
    Oct 2008
    Posts
    1,088

    Re: C Windows winapi + multi-threading (HANDLE)_beginthreadex fail

    as suggested by D_Drmmr, a minimal code change would be

    Code:
    char line_buffer[200][BUFSIZ];
    char line_number;
    
    /* ... */
    
    line_number = 0;
    HANDLE hThreadArray[200];
    while (fgets(line_buffer[line_number], sizeof(line_buffer[line_number]), infile)) {
      unsigned threadID;
      hThreadArray[line_number] = (HANDLE)_beginthreadex(0, 0, isAlive, line_buffer[line_number], 0, &threadID);
      ++line_number;
    }
    WaitForMultipleObjects(line_number, hThreadArray, TRUE, INFINITE);
    
    // ...
    ( ignoring issues like possible buffer overruns, unchecked retun codes, etc ... )

    alternatively, you could just pass the file path and a liner number to each thread, that in turn will open its own file stream seeking to the appropriate line.
    Last edited by superbonzo; January 28th, 2013 at 08:13 AM.

  7. #7
    Join Date
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    Location
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    Posts
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    Re: C Windows winapi + multi-threading (HANDLE)_beginthreadex fail

    Quote Originally Posted by exitthematrix View Post
    By "that works" I mean using "printf("%s", line_buffer)" that prints out every line out from my text.
    There's little point in being vague if you want to get help. At the very least, you could post the code.
    What you have now is a race condition, because you are writing (in the main thread) to the same memory you are reading from in the worker threads. That means that the results could be different on each run of your program.
    Cheers, D Drmmr

    Please put [code][/code] tags around your code to preserve indentation and make it more readable.

    As long as man ascribes to himself what is merely a posibility, he will not work for the attainment of it. - P. D. Ouspensky

  8. #8
    Join Date
    Jan 2013
    Posts
    5

    Re: C Windows winapi + multi-threading (HANDLE)_beginthreadex fail

    Thanks!

    I did it like this:

    Code:
    	HANDLE hThreadArray[200];
      	char str[MAX];
      	char *x[MAX];
      	int i = 0;
        while(!feof(infile)) {
            while(fgets(str, sizeof str, infile)) {
            	unsigned threadID;
                x[i] = strdup(str);
                //printf("%s", str);
                //printf("%s", *(x+i));
                hThreadArray[i] = (HANDLE)_beginthreadex(0, 0, isAlive, *(x+i), 0, &threadID);
                i++;
            }
    	}
    	
      WaitForMultipleObjects(i, hThreadArray, TRUE, INFINITE);

  9. #9
    Join Date
    Jan 2013
    Posts
    5

    Re: C Windows winapi + multi-threading (HANDLE)_beginthreadex fail

    This is my finished code, I added timeout also but seems to hang connected if no response back, otherwise works:

    Code:
    #include <windows.h>
    #include <stdio.h>
    #include <string.h>
    #include <winsock.h>
    #include <process.h>
    #include <string.h>
    
    #pragma comment(lib, "wsock32.lib")
    
    #define MAX 10000
    
    unsigned int _stdcall isAlive(void *ptr)
    {
      struct sockaddr_in blah;
      struct hostent *he;
      WSADATA wsaData;
      int i;
      WORD wVersionRequested;
      SOCKET sock;
      char* addr = (char*)ptr;
    
      char buff[1024];
      char *request;
      request="GET /alive.php HTTP/1.0\n\n";
      char *fmsg="ALIVE";
    
      wVersionRequested = MAKEWORD(1, 1);
      if (WSAStartup(wVersionRequested , &wsaData)){
        printf("Winsock Initialization failed.\n");
        return(1);
      }
    
      if ((sock=socket(AF_INET,SOCK_STREAM,0))==INVALID_SOCKET){
        printf("Can not create socket.\n");
        return(1);
      }
      sock = socket(AF_INET,SOCK_STREAM,0);
      blah.sin_family = AF_INET;
      blah.sin_port = htons(80);
      blah.sin_addr.s_addr = inet_addr(addr);
    
      if ((he=gethostbyname(addr))!=NULL){
        memcpy((char *)&blah.sin_addr.s_addr,he->h_addr,he->h_length);
      }
      else{
        if((blah.sin_addr.s_addr=inet_addr(addr))==-1){
          WSACleanup();
          return(1);
        }
      }
    
      if (connect(sock,(struct sockaddr*)&blah,sizeof(blah))==0){
        send(sock,request,strlen(request),0);
        recv(sock,buff,sizeof(buff),0);
        if(strstr(buff,fmsg)!=NULL){
          printf("ALIVE: %s", addr);
        }
      }
    
      closesocket(sock);
      WSACleanup();
      _endthreadex(0);
      return(1);
    }
    
    int main(int argc,char *argv[])
    {
      if(argc!=2){
        printf("Usage: %s <webservers list>\n", argv[0]);
        return(1);
      }
    
      char *inname = argv[1];
      FILE *infile;
      char line_buffer[BUFSIZ];
      char line_number;
    
      infile = fopen(inname, "r");
      if (!infile) {
        printf("Couldn't open file %s for reading.\n", inname);
        return 0;
      }
    
      HANDLE hThreadArray[200];
      char str[MAX];
      char *x[MAX];
      int i = 0;
      while(!feof(infile)) {
        while(fgets(str, sizeof str, infile)) {
          unsigned threadID;
          x[i] = strdup(str);
          //printf("%s", *(x+i)); // DEBUG
          hThreadArray[i] = (HANDLE)_beginthreadex(0, 0, isAlive, *(x+i), 0, &threadID);
          i++;
          }
      }
    	
      WaitForMultipleObjects(i, hThreadArray, TRUE, INFINITE);
      fclose(infile);
      return 0;
    }

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