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code/smart-select.c

+/* smart-select.c
+ *
+ * Copyright (c) 2000 Sean Walton and Macmillan Publishers.  Use may be in
+ * whole or in part in accordance to the General Public License (GPL).
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+*/
+
+/*****************************************************************************/
+/*** smart-select.c                                                        ***/
+/***                                                                       ***/
+/*** The smart select combines preforking with the select() call to keep   ***/
+/*** the select descriptor arrays small.                                   ***/
+/*****************************************************************************/
+
+#include <stdio.h>
+#include <sys/socket.h>
+#include <resolv.h>
+#include <unistd.h>
+#include <signal.h>
+#include <sys/time.h>
+
+#define MAXPROCESSES	5
+#define MAXCONNECTIONS	2
+
+int NumChildren=0;
+
+/*---------------------------------------------------------------------*/
+/*--- sig_child - SIGCHLD                                           ---*/
+/*---------------------------------------------------------------------*/
+void sig_child(int signum)
+{
+	wait(0);
+	NumChildren--;
+}
+
+/*---------------------------------------------------------------------*/
+/*--- servlet - each servlet accepts a connection and keeps track   ---*/
+/*--- of it using a select() statement.                             ---*/
+/*---------------------------------------------------------------------*/
+void servlet(int server)
+{	fd_set set, set_all; 
+	int maxfd = server;
+	int ceiling=0;
+	int i;
+
+	FD_ZERO(&set);
+	FD_ZERO(&set_all);
+
+	FD_SET(server, &set_all);
+
+	for (;;) {   
+	  
+	  struct timeval timeout={40,0}; /* 40 seconds */
+	  
+	  set = set_all;
+	  
+	  /*---Wait for some action---*/
+	  if ( select(maxfd+1, &set, 0, 0, &timeout) > 0 ) {
+        	/*---If new connection, connect and add to list---*/
+
+	    for ( i = 0; i < maxfd+1; i++ ) {
+
+	      if ( FD_ISSET(i, &set) ) {
+
+		if ( i == server ) {
+		  if ( ceiling < MAXCONNECTIONS ) { 
+		    int client = accept(server, 0, 0);
+		    if ( maxfd < client )
+		      maxfd = client;
+		    FD_SET(client, &set_all);
+		    ceiling++;
+		    printf("select process #%d: %d connected\n", getpid(), ceiling);
+		  }
+		}		
+
+	 
+		else {
+
+		    char buffer[1024];
+		    int bytes;
+		    
+		    bytes = recv(i, buffer, sizeof(buffer), 0);
+
+		    write(0, buffer, bytes);
+
+		    if ( bytes == 0 ) {
+		      close(i);
+		      FD_CLR(i, &set_all);
+		      ceiling--;
+		      printf("select process #%d: %d connected\n",
+			     getpid(), ceiling);
+		    }
+		    else					/* process the request */
+		      send(i, buffer, bytes, 0);
+		}
+
+		
+	      }
+
+	    }
+	  }
+	}
+	exit(0);
+}
+
+/*---------------------------------------------------------------------*/
+/*--- main - set up server and maintain the number of living servlets--*/
+/*---------------------------------------------------------------------*/
+int main(int count, char *strings[])
+{	int sd;
+	struct sockaddr_in addr;
+	struct sigaction act;
+
+	if ( count != 2 )
+	{
+		printf("usage: %s <port>\n", strings[0]);
+		exit(0);
+	}
+	bzero(&act, sizeof(act));
+	act.sa_handler = sig_child;
+	act.sa_flags = SA_NOCLDSTOP | SA_RESTART;
+	if ( sigaction(SIGCHLD, &act, 0) != 0 )
+		perror("sigaction()");
+
+	sd = socket(PF_INET, SOCK_STREAM, 0);
+	bzero(&addr, sizeof(addr));
+	addr.sin_family = AF_INET;
+	addr.sin_port = htons(atoi(strings[1]));
+	addr.sin_addr.s_addr = INADDR_ANY;
+	if ( bind(sd, (struct sockaddr *)&addr, sizeof(addr)) == 0 )
+	{
+		listen(sd, 15);
+		for (;;)
+		{
+			if ( NumChildren < MAXPROCESSES )
+			{	int pid;
+
+				if ( (pid = fork()) == 0 )
+					servlet(sd);
+				else if ( pid > 0 )
+					NumChildren++;
+				else
+					perror("fork()");
+			}
+			else
+				sleep(1);
+		}
+	}
+	else
+		perror("bind()");
+	return 0;
+}