releasing version 1.4-1
[debian/cpulimit.git] / cpulimit.c
index bf912d6..ba41986 100644 (file)
@@ -1,50 +1,26 @@
 /**
- *
- * cpulimit - a cpu limiter for Linux
- *
- * Copyright (C) 2005-2008, by:  Angelo Marletta <marlonx80@hotmail.com>
- *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public License
- * as published by the Free Software Foundation; either version 2
- * of the License, or (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ * This program is licensed under the GNU General Public License,
+ * version 2. A copy of the license can be found in the accompanying
+ * LICENSE file.
  *
  **********************************************************************
  *
- * This is a simple program to limit the cpu usage of a process
+ * Simple program to limit the cpu usage of a process
  * If you modify this code, send me a copy please
  *
- * Date:    15/2/2008
- * Version: 1.2 alpha
- * Get the latest version at: http://cpulimit.sourceforge.net
+ * Author:  Angelo Marletta
+ * Date:    26/06/2005
+ * Version: 1.1
  *
- * Changelog:
- * - reorganization of the code, splitted in more source files
- * - control function process_monitor() optimized by eliminating an unnecessary loop
- * - experimental support for multiple control of children processes and threads
- *   children detection algorithm seems heavy because of the amount of code,
- *   but it's designed to be scalable when there are a lot of children processes
- * - cpu count detection, i.e. if you have 4 cpu, it is possible to limit up to 400%
- * - in order to avoid deadlock, cpulimit prevents to limit itself
- * - option --path eliminated, use --exe instead both for absolute path and file name
- * - deleted almost every setpriority(), just set it once at startup
- * - minor enhancements and bugfixes
+ * Modifications and updates by: Jesse Smith
+ * Date: May 4, 2011
+ * Version 1.2
  *
  */
 
 
 #include <getopt.h>
 #include <stdio.h>
-#include <fcntl.h>
 #include <stdlib.h>
 #include <time.h>
 #include <sys/time.h>
 #include <dirent.h>
 #include <errno.h>
 #include <string.h>
+#include <limits.h>    // for compatibility
 
-#include "process.h"
-#include "procutils.h"
-#include "list.h"
 
-//some useful macro
-#define MIN(a,b) (a<b?a:b)
-#define MAX(a,b) (a>b?a:b)
-#define print_caption()        printf("\n%%CPU\twork quantum\tsleep quantum\tactive rate\n")
-//control time slot in microseconds
-//each slot is splitted in a working slice and a sleeping slice
-#define CONTROL_SLOT 100000
-
-#define MAX_PRIORITY -10
-
-//the "family"
-struct process_family pf;
-//pid of cpulimit
-int cpulimit_pid;
-//name of this program (maybe cpulimit...)
-char *program_name;
+//kernel time resolution (inverse of one jiffy interval) in Hertz
+//i don't know how to detect it, then define to the default (not very clean!)
+#define HZ 100
 
-/* CONFIGURATION VARIABLES */
+//some useful macro
+#define min(a,b) (a<b?a:b)
+#define max(a,b) (a>b?a:b)
 
+//pid of the controlled process
+int pid=0;
+//executable file name
+char *program_name;
 //verbose mode
-int verbose = 0;
-//lazy mode (exits if there is no process)
-int lazy = 0;
-
-//how many cpu do we have?
-int get_cpu_count()
-{
-       FILE *fd;
-       int cpu_count = 0;
-       char line[100];
-       fd = fopen("/proc/stat", "r");
-       if (fd < 0)
-               return 0; //are we running Linux??
-       while (fgets(line,sizeof(line),fd)!=NULL) {
-               if (strncmp(line, "cpu", 3) != 0) break;
-               cpu_count++;
-       }
-       fclose(fd);
-       return cpu_count - 1;
+int verbose=0;
+//lazy mode
+int lazy=0;
+// is higher priority nice possible?
+int nice_lim;
+
+//reverse byte search
+void *memrchr(const void *s, int c, size_t n);
+
+//return ta-tb in microseconds (no overflow checks!)
+inline long timediff(const struct timespec *ta,const struct timespec *tb) {
+    unsigned long us = (ta->tv_sec-tb->tv_sec)*1000000 + (ta->tv_nsec/1000 - tb->tv_nsec/1000);
+    return us;
 }
 
-//return t1-t2 in microseconds (no overflow checks, so better watch out!)
-inline unsigned long timediff(const struct timespec *t1,const struct timespec *t2)
-{
-       return (t1->tv_sec - t2->tv_sec) * 1000000 + (t1->tv_nsec/1000 - t2->tv_nsec/1000);
-}
-
-//returns t1-t2 in microseconds
-inline unsigned long long tv_diff(struct timeval *t1, struct timeval *t2)
-{
-       return ((unsigned long long)(t1->tv_sec - t2->tv_sec)) * 1000000ULL + t1->tv_usec - t2->tv_usec;
-}
-
-//SIGINT and SIGTERM signal handler
-void quit(int sig)
-{
-       //let all the processes continue if stopped
-       struct list_node *node = NULL;
-       for (node=pf.members.first; node!= NULL; node=node->next) {
-               struct process *p = (struct process*)(node->data);
-               process_close(p->history);
-               kill(p->pid, SIGCONT);
+int waitforpid(int pid) {
+       //switch to low priority
+       // if (setpriority(PRIO_PROCESS,getpid(),19)!=0) {
+        if ( (nice_lim < INT_MAX) && 
+             (setpriority(PRIO_PROCESS, getpid(), 19) != 0) ) {
+               printf("Warning: cannot renice\n");
        }
-       //free all the memory
-       cleanup_process_family(&pf);
-       exit(0);
-}
 
-void print_usage(FILE *stream, int exit_code)
-{
-       fprintf(stream, "Usage: %s TARGET [OPTIONS...]\n",program_name);
-       fprintf(stream, "   TARGET must be exactly one of these:\n");
-       fprintf(stream, "      -p, --pid=N        pid of the process (implies -z)\n");
-       fprintf(stream, "      -e, --exe=FILE     name of the executable program file or absolute path name\n");
-       fprintf(stream, "   OPTIONS\n");
-       fprintf(stream, "      -l, --limit=N      percentage of cpu allowed from 0 to 100 (required)\n");
-       fprintf(stream, "      -v, --verbose      show control statistics\n");
-       fprintf(stream, "      -z, --lazy         exit if there is no suitable target process, or if it dies\n");
-       fprintf(stream, "      -h, --help         display this help and exit\n");
-       exit(exit_code);
-}
-
-void limit_process(int pid, float limit)
-{
-       //slice of the slot in which the process is allowed to run
-       struct timespec twork;
-       //slice of the slot in which the process is stopped
-       struct timespec tsleep;
-       //when the last twork has started
-       struct timespec startwork;
-       //when the last twork has finished
-       struct timespec endwork;
-       //initialization
-       memset(&twork, 0, sizeof(struct timespec));
-       memset(&tsleep, 0, sizeof(struct timespec));
-       memset(&startwork, 0, sizeof(struct timespec));
-       memset(&endwork, 0, sizeof(struct timespec));   
-       //last working time in microseconds
-       unsigned long workingtime = 0;
-       int i = 0;
-
-       //build the family
-       create_process_family(&pf, pid);
-       struct list_node *node;
-       
-       if (verbose) printf("Members in the family owned by %d: %d\n", pf.father, pf.members.count);
+       int i=0;
 
        while(1) {
 
-               if (i%100==0 && verbose) print_caption();
-
-               if (i%10==0) {
-                       //update the process family (checks only for new members)
-                       int newborn = check_new_members(&pf);
-                       if (newborn) {
-                               printf("%d new children processes detected (", newborn);
-                               int j;
-                               node = pf.members.last;
-                               for (j=0; j<newborn; j++) {
-                                       printf("%d", ((struct process*)(node->data))->pid);
-                                       if (j<newborn-1) printf(" ");
-                                       node = node->previous;
+               DIR *dip;
+               struct dirent *dit;
+
+               //open a directory stream to /proc directory
+               if ((dip = opendir("/proc")) == NULL) {
+                       perror("opendir");
+                       return -1;
+               }
+
+               //read in from /proc and seek for process dirs
+               while ((dit = readdir(dip)) != NULL) {
+                       //get pid
+                       if (pid==atoi(dit->d_name)) {
+                               //pid detected
+                               if (kill(pid,SIGSTOP)==0 &&  kill(pid,SIGCONT)==0) {
+                                       //process is ok!
+                                        if (closedir(dip) == -1) {
+                                           perror("closedir");
+                                           return -1;
+                                        }
+                                       goto done;
+                               }
+                               else {
+                                       fprintf(stderr,"Error: Process %d detected, but you don't have permission to control it\n",pid);
                                }
-                               printf(")\n");
                        }
                }
 
-               //total cpu actual usage (range 0-1)
-               //1 means that the processes are using 100% cpu
-               float pcpu = 0;
-               //rate at which we are keeping active the processes (range 0-1)
-               //1 means that the process are using all the twork slice
-               float workingrate = 0;
-
-               //estimate how much the controlled processes are using the cpu in the working interval
-               for (node=pf.members.first; node!=NULL; node=node->next) {
-                       struct process *proc = (struct process*)(node->data);
-                       if (process_monitor(proc->history, workingtime, &(proc->history->usage))==-1) {
-                               //process is dead, remove it from family
-                               remove_process_from_family(&pf, proc->pid);
-                               fprintf(stderr,"Process %d dead!\n", proc->pid);
+               //close the dir stream and check for errors
+               if (closedir(dip) == -1) {
+                       perror("closedir");
+                       return -1;
+               }
+
+               //no suitable target found
+               if (i++==0) {
+                       if (lazy) {
+                               fprintf(stderr,"No process found\n");
+                               exit(2);
+                       }
+                       else {
+                               printf("Warning: no target process found. Waiting for it...\n");
                        }
-                       pcpu += proc->history->usage.pcpu;
-                       workingrate += proc->history->usage.workingrate;
                }
-               //average value
-               workingrate /= pf.members.count;
 
-               //TODO: make workingtime customized for each process, now it's equal for all
+               //sleep for a while
+               sleep(2);
+       }
 
-               //adjust work and sleep time slices
-               if (pcpu>0) {
-                       twork.tv_nsec = MIN(CONTROL_SLOT*limit*1000/pcpu*workingrate,CONTROL_SLOT*1000);
-               }
-               else if (pcpu==0) {
-                       twork.tv_nsec = CONTROL_SLOT*1000;
-               }
-               else if (pcpu==-1) {
-                       //not yet a valid idea of cpu usage
-                       pcpu = limit;
-                       workingrate = limit;
-                       twork.tv_nsec = MIN(CONTROL_SLOT*limit*1000,CONTROL_SLOT*1000);
-               }
-               tsleep.tv_nsec = CONTROL_SLOT*1000-twork.tv_nsec;
+done:
+       printf("Process %d detected\n",pid);
+       //now set high priority, if possible
+       // if (setpriority(PRIO_PROCESS,getpid(),-20)!=0) {
+        if ( (nice_lim < INT_MAX) &&
+             (setpriority(PRIO_PROCESS, getpid(), nice_lim) != 0) ) {
+               printf("Warning: cannot renice.\nTo work better you should run this program as root.\n");
+       }
+       return 0;
 
-               if (verbose && i%10==0 && i>0) {
-                       printf("%0.2f%%\t%6ld us\t%6ld us\t%0.2f%%\n",pcpu*100,twork.tv_nsec/1000,tsleep.tv_nsec/1000,workingrate*100);
+}
+
+//this function periodically scans process list and looks for executable path names
+//it should be executed in a low priority context, since precise timing does not matter
+//if a process is found then its pid is returned
+//process: the name of the wanted process, can be an absolute path name to the executable file
+//         or simply its name
+//return: pid of the found process
+int getpidof(const char *process) {
+
+       //set low priority
+       // if (setpriority(PRIO_PROCESS,getpid(),19)!=0) {
+        if ( (nice_lim < INT_MAX) &&
+             (setpriority(PRIO_PROCESS, getpid(), 19) != 0) ) {
+               printf("Warning: cannot renice\n");
+       }
+
+       char exelink[20];
+       char exepath[PATH_MAX+1];
+       int pid=0;
+       int i=0;
+
+       while(1) {
+
+               DIR *dip;
+               struct dirent *dit;
+
+               //open a directory stream to /proc directory
+               if ((dip = opendir("/proc")) == NULL) {
+                       perror("opendir");
+                       return -1;
                }
 
-               //resume processes
-               for (node=pf.members.first; node!=NULL; node=node->next) {
-                       struct process *proc = (struct process*)(node->data);
-                       if (kill(proc->pid,SIGCONT)!=0) {
-                               //process is dead, remove it from family
-                               fprintf(stderr,"Process %d dead!\n", proc->pid);
-                               remove_process_from_family(&pf, proc->pid);
+               //read in from /proc and seek for process dirs
+               while ((dit = readdir(dip)) != NULL) {
+                       //get pid
+                       pid=atoi(dit->d_name);
+                       if (pid>0) {
+                               sprintf(exelink,"/proc/%d/exe",pid);
+                               int size=readlink(exelink,exepath,sizeof(exepath));
+                               if (size>0) {
+                                       int found=0;
+                                       if (process[0]=='/' && strncmp(exepath,process,size)==0 && size==strlen(process)) {
+                                               //process starts with / then it's an absolute path
+                                               found=1;
+                                       }
+                                       else {
+                                               //process is the name of the executable file
+                                               if (strncmp(exepath+size-strlen(process),process,strlen(process))==0) {
+                                                       found=1;
+                                               }
+                                       }
+                                       if (found==1) {
+                                               if (kill(pid,SIGSTOP)==0 &&  kill(pid,SIGCONT)==0) {
+                                                       //process is ok!
+                                                        if (closedir(dip) == -1) {
+                                                          perror("closedir");
+                                                          return -1;
+                                                        }
+                                                       goto done;
+                                               }
+                                               else {
+                                                       fprintf(stderr,"Error: Process %d detected, but you don't have permission to control it\n",pid);
+                                               }
+                                       }
+                               }
                        }
                }
 
-               //now processes are free to run (same working slice for all)
-               clock_gettime(CLOCK_REALTIME,&startwork);
-               nanosleep(&twork,NULL);
-               clock_gettime(CLOCK_REALTIME,&endwork);
-               workingtime = timediff(&endwork,&startwork);
-
-               //stop processes, they have worked enough
-               //resume processes
-               for (node=pf.members.first; node!=NULL; node=node->next) {
-                       struct process *proc = (struct process*)(node->data);
-                       if (kill(proc->pid,SIGSTOP)!=0) {
-                               //process is dead, remove it from family
-                               fprintf(stderr,"Process %d dead!\n", proc->pid);
-                               remove_process_from_family(&pf, proc->pid);
+               //close the dir stream and check for errors
+               if (closedir(dip) == -1) {
+                       perror("closedir");
+                       return -1;
+               }
+
+               //no suitable target found
+               if (i++==0) {
+                       if (lazy) {
+                               fprintf(stderr,"No process found\n");
+                               exit(2);
+                       }
+                       else {
+                               printf("Warning: no target process found. Waiting for it...\n");
                        }
                }
-               //now the process is forced to sleep
-               nanosleep(&tsleep,NULL);
-               i++;
+
+               //sleep for a while
+               sleep(2);
        }
-       cleanup_process_family(&pf);
+
+done:
+       printf("Process %d detected\n",pid);
+       //now set high priority, if possible
+       // if (setpriority(PRIO_PROCESS,getpid(),-20)!=0) {
+        if ( (nice_lim < INT_MAX) &&
+             (setpriority(PRIO_PROCESS, getpid(), nice_lim) != 0) ) {
+               printf("Warning: cannot renice.\nTo work better you should run this program as root.\n");
+       }
+       return pid;
+
+}
+
+//SIGINT and SIGTERM signal handler
+void quit(int sig) {
+       //let the process continue if it's stopped
+       kill(pid,SIGCONT);
+       printf("Exiting...\n");
+       exit(0);
+}
+
+//get jiffies count from /proc filesystem
+int getjiffies(int pid) {
+       static char stat[20];
+       static char buffer[1024];
+        char *p;
+       sprintf(stat,"/proc/%d/stat",pid);
+       FILE *f=fopen(stat,"r");
+       if (f==NULL) return -1;
+       p = fgets(buffer,sizeof(buffer),f);
+       fclose(f);
+       // char *p=buffer;
+        if (p)
+        {
+         p=memchr(p+1,')',sizeof(buffer)-(p-buffer));
+         int sp=12;
+         while (sp--)
+               p=memchr(p+1,' ',sizeof(buffer)-(p-buffer));
+         //user mode jiffies
+         int utime=atoi(p+1);
+         p=memchr(p+1,' ',sizeof(buffer)-(p-buffer));
+         //kernel mode jiffies
+         int ktime=atoi(p+1);
+         return utime+ktime;
+        }
+        // could not read info
+        return -1;
+}
+
+//process instant photo
+struct process_screenshot {
+       struct timespec when;   //timestamp
+       int jiffies;    //jiffies count of the process
+       int cputime;    //microseconds of work from previous screenshot to current
+};
+
+//extracted process statistics
+struct cpu_usage {
+       float pcpu;
+       float workingrate;
+};
+
+//this function is an autonomous dynamic system
+//it works with static variables (state variables of the system), that keep memory of recent past
+//its aim is to estimate the cpu usage of the process
+//to work properly it should be called in a fixed periodic way
+//perhaps i will put it in a separate thread...
+int compute_cpu_usage(int pid,int last_working_quantum,struct cpu_usage *pusage) {
+       #define MEM_ORDER 10
+       //circular buffer containing last MEM_ORDER process screenshots
+       static struct process_screenshot ps[MEM_ORDER];
+       //the last screenshot recorded in the buffer
+       static int front=-1;
+       //the oldest screenshot recorded in the buffer
+       static int tail=0;
+
+       if (pusage==NULL) {
+               //reinit static variables
+               front=-1;
+               tail=0;
+               return 0;
+       }
+
+       //let's advance front index and save the screenshot
+       front=(front+1)%MEM_ORDER;
+       int j=getjiffies(pid);
+       if (j>=0) ps[front].jiffies=j;
+       else return -1; //error: pid does not exist
+       clock_gettime(CLOCK_REALTIME,&(ps[front].when));
+       ps[front].cputime=last_working_quantum;
+
+       //buffer actual size is: (front-tail+MEM_ORDER)%MEM_ORDER+1
+       int size=(front-tail+MEM_ORDER)%MEM_ORDER+1;
+
+       if (size==1) {
+               //not enough samples taken (it's the first one!), return -1
+               pusage->pcpu=-1;
+               pusage->workingrate=1;
+               return 0;
+       }
+       else {
+               //now we can calculate cpu usage, interval dt and dtwork are expressed in microseconds
+               long dt=timediff(&(ps[front].when),&(ps[tail].when));
+               long dtwork=0;
+               int i=(tail+1)%MEM_ORDER;
+               int max=(front+1)%MEM_ORDER;
+               do {
+                       dtwork+=ps[i].cputime;
+                       i=(i+1)%MEM_ORDER;
+               } while (i!=max);
+               int used=ps[front].jiffies-ps[tail].jiffies;
+               float usage=(used*1000000.0/HZ)/dtwork;
+               pusage->workingrate=1.0*dtwork/dt;
+               pusage->pcpu=usage*pusage->workingrate;
+               if (size==MEM_ORDER)
+                       tail=(tail+1)%MEM_ORDER;
+               return 0;
+       }
+       #undef MEM_ORDER
+}
+
+void print_caption() {
+       printf("\n%%CPU\twork quantum\tsleep quantum\tactive rate\n");
+}
+
+void print_usage(FILE *stream,int exit_code) {
+       fprintf(stream, "Usage: %s TARGET [OPTIONS...]\n",program_name);
+       fprintf(stream, "   TARGET must be exactly one of these:\n");
+       fprintf(stream, "      -p, --pid=N        pid of the process\n");
+       fprintf(stream, "      -e, --exe=FILE     name of the executable program file\n");
+       fprintf(stream, "      -P, --path=PATH    absolute path name of the executable program file\n");
+       fprintf(stream, "   OPTIONS\n");
+        fprintf(stream, "      -b  --background   run in background\n");
+       fprintf(stream, "      -l, --limit=N      percentage of cpu allowed from 0 to 100 (mandatory)\n");
+       fprintf(stream, "      -v, --verbose      show control statistics\n");
+       fprintf(stream, "      -z, --lazy         exit if there is no suitable target process, or if it dies\n");
+       fprintf(stream, "      -h, --help         display this help and exit\n");
+       exit(exit_code);
 }
 
 int main(int argc, char **argv) {
@@ -268,60 +368,66 @@ int main(int argc, char **argv) {
        //get program name
        char *p=(char*)memrchr(argv[0],(unsigned int)'/',strlen(argv[0]));
        program_name = p==NULL?argv[0]:(p+1);
-       cpulimit_pid = getpid();
-
-       //argument variables
-       const char *exe = NULL;
-       int perclimit = 0;
-       int pid_ok = 0;
-       int process_ok = 0;
-       int limit_ok = 0;
-       int pid = 0;
-
+        int run_in_background = 0;
        //parse arguments
        int next_option;
-    int option_index = 0;
-       //A string listing valid short options letters
-       const char* short_options = "p:e:l:vzh";
-       //An array describing valid long options
+       /* A string listing valid short options letters. */
+       const char* short_options="p:e:P:l:bvzh";
+       /* An array describing valid long options. */
        const struct option long_options[] = {
-               { "pid",        required_argument, NULL,     'p' },
-               { "exe",        required_argument, NULL,     'e' },
-               { "limit",      required_argument, NULL,     'l' },
-               { "verbose",    no_argument,       &verbose, 'v' },
-               { "lazy",       no_argument,       &lazy,    'z' },
-               { "help",       no_argument,       NULL,     'h' },
-               { 0,            0,                 0,         0  }
+               { "pid", required_argument, NULL, 'p' },
+               { "exe", required_argument, NULL, 'e' },
+               { "path", required_argument, NULL, 'P' },
+               { "limit", required_argument, NULL, 'l' },
+                { "background", no_argument, NULL, 'b' },
+               { "verbose", no_argument, NULL, 'v' },
+               { "lazy", no_argument, NULL, 'z' },
+               { "help", no_argument, NULL, 'h' },
+               { NULL, 0, NULL, 0 }
        };
+       //argument variables
+       const char *exe=NULL;
+       const char *path=NULL;
+       int perclimit=0;
+       int pid_ok=0;
+       int process_ok=0;
+       int limit_ok=0;
+        struct rlimit maxlimit;
 
        do {
-               next_option = getopt_long(argc, argv, short_options,long_options, &option_index);
+               next_option = getopt_long (argc, argv, short_options,long_options, NULL);
                switch(next_option) {
+                        case 'b':
+                                run_in_background = 1;
+                                break;
                        case 'p':
-                               pid = atoi(optarg);
-                               //todo: verify pid is valid
-                               pid_ok = 1;
-                               process_ok = 1;
+                               pid=atoi(optarg);
+                               pid_ok=1;
+                                lazy = 1;
                                break;
                        case 'e':
-                               exe = optarg;
-                               process_ok = 1;
+                               exe=optarg;
+                               process_ok=1;
+                               break;
+                       case 'P':
+                               path=optarg;
+                               process_ok=1;
                                break;
                        case 'l':
-                               perclimit = atoi(optarg);
-                               limit_ok = 1;
+                               perclimit=atoi(optarg);
+                               limit_ok=1;
                                break;
                        case 'v':
-                               verbose = 1;
+                               verbose=1;
                                break;
                        case 'z':
-                               lazy = 1;
+                               lazy=1;
                                break;
                        case 'h':
-                               print_usage(stdout, 1);
+                               print_usage (stdout, 1);
                                break;
                        case '?':
-                               print_usage(stderr, 1);
+                               print_usage (stderr, 1);
                                break;
                        case -1:
                                break;
@@ -330,91 +436,184 @@ int main(int argc, char **argv) {
                }
        } while(next_option != -1);
 
-       if (pid!=0) {
-               lazy = 1;
-       }
-       
-       if (!process_ok) {
-               fprintf(stderr,"Error: You must specify a target process, by name or by PID\n");
-               print_usage(stderr, 1);
+       if (!process_ok && !pid_ok) {
+               fprintf(stderr,"Error: You must specify a target process\n");
+               print_usage (stderr, 1);
                exit(1);
        }
-       if (pid_ok && exe!=NULL) {
-               fprintf(stderr, "Error: You must specify exactly one process, by name or by PID\n");
-               print_usage(stderr, 1);
+       if ((exe!=NULL && path!=NULL) || (pid_ok && (exe!=NULL || path!=NULL))) {
+               fprintf(stderr,"Error: You must specify exactly one target process\n");
+               print_usage (stderr, 1);
                exit(1);
        }
        if (!limit_ok) {
-               fprintf(stderr,"Error: You must specify a cpu limit percentage\n");
-               print_usage(stderr, 1);
+               fprintf(stderr,"Error: You must specify a cpu limit\n");
+               print_usage (stderr, 1);
                exit(1);
        }
-       float limit = perclimit/100.0;
-       int cpu_count = get_cpu_count();
-       if (limit<0 || limit >cpu_count) {
-               fprintf(stderr,"Error: limit must be in the range 0-%d00\n", cpu_count);
-               print_usage(stderr, 1);
+       float limit=perclimit/100.0;
+       if (limit <= 0.00) // || limit >1) {
+        {
+               fprintf(stderr,"Error: limit must be greater than 0\n");
+               print_usage (stderr, 1);
                exit(1);
        }
+
+        // check to see if we should fork
+        if (run_in_background)
+        {
+             pid_t process_id;
+             process_id = fork();
+             if (! process_id)
+                exit(0);
+             else
+             {
+                setsid();
+                process_id = fork();
+                if (process_id)
+                  exit(0);
+             }
+        }
+
        //parameters are all ok!
-       signal(SIGINT, quit);
-       signal(SIGTERM, quit);
-
-       //try to renice with the best value
-       int old_priority = getpriority(PRIO_PROCESS, 0);
-       int priority = old_priority;
-       while (setpriority(PRIO_PROCESS, 0, priority-1) == 0 && priority>MAX_PRIORITY) {
-               priority--;     
-       }
-       if (priority != old_priority) {
-               printf("Priority changed to %d\n", priority);
+       signal(SIGINT,quit);
+       signal(SIGTERM,quit);
+
+       if (setpriority(PRIO_PROCESS,getpid(),-20)!=0) {
+       //if that failed, check if we have a limit 
+        // by how much we can raise the priority
+#ifdef RLIMIT_NICE 
+//check if non-root can even make changes 
+// (ifdef because it's only available in linux >= 2.6.13)
+               nice_lim=getpriority(PRIO_PROCESS,getpid());
+               getrlimit(RLIMIT_NICE, &maxlimit);
+
+//if we can do better then current
+               if( (20 - (signed)maxlimit.rlim_cur) < nice_lim &&  
+                   setpriority(PRIO_PROCESS,getpid(),
+                    20 - (signed)maxlimit.rlim_cur)==0 //and it actually works
+                 ) {
+
+                       //if we can do better, but not by much, warn about it
+                       if( (nice_lim - (20 - (signed)maxlimit.rlim_cur)) < 9) 
+                        {
+                       printf("Warning, can only increase priority by %d.\n",                                nice_lim - (20 - (signed)maxlimit.rlim_cur));
+                       }
+                        //our new limit
+                       nice_lim = 20 - (signed)maxlimit.rlim_cur; 
+
+               } else 
+// otherwise don't try to change priority. 
+// The below will also run if it's not possible 
+// for non-root to change priority
+#endif
+               {
+                       printf("Warning: cannot renice.\nTo work better you should run this program as root, or adjust RLIMIT_NICE.\nFor example in /etc/security/limits.conf add a line with: * - nice -10\n\n");
+                       nice_lim=INT_MAX;
+               }
+       } else {
+               nice_lim=-20;
        }
+       //don't bother putting setpriority back down, 
+        // since getpidof and waitforpid twiddle it anyway
+
+
+
+       //time quantum in microseconds. it's splitted in a working period and a sleeping one
+       int period=100000;
+       struct timespec twork,tsleep;   //working and sleeping intervals
+       memset(&twork,0,sizeof(struct timespec));
+       memset(&tsleep,0,sizeof(struct timespec));
+
+wait_for_process:
+
+       //look for the target process..or wait for it
+       if (exe!=NULL)
+               pid=getpidof(exe);
+       else if (path!=NULL)
+               pid=getpidof(path);
        else {
-               printf("Cannot change priority\n");
+               waitforpid(pid);
        }
-       
+       //process detected...let's play
+
+       //init compute_cpu_usage internal stuff
+       compute_cpu_usage(0,0,NULL);
+       //main loop counter
+       int i=0;
+
+       struct timespec startwork,endwork;
+       long workingtime=0;             //last working time in microseconds
+
+       if (verbose) print_caption();
+
+       float pcpu_avg=0;
+
+       //here we should already have high priority, for time precision
        while(1) {
-               //look for the target process..or wait for it
-               int ret = 0;
-               if (pid_ok) {
-                       //search by pid
-                       ret = look_for_process_by_pid(pid);
-                       if (ret == 0) {
-                               printf("No process found\n");
-                       }
-                       else if (ret < 0) {
-                               printf("Process found but you aren't allowed to control it\n");
-                       }
+
+               //estimate how much the controlled process is using the cpu in its working interval
+               struct cpu_usage cu;
+               if (compute_cpu_usage(pid,workingtime,&cu)==-1) {
+                       fprintf(stderr,"Process %d dead!\n",pid);
+                       if (lazy) exit(2);
+                       //wait until our process appears
+                       goto wait_for_process;          
                }
-               else {
-                       //search by file or path name
-                       ret = look_for_process_by_name(exe);
-                       if (ret == 0) {
-                               printf("No process found\n");
-                       }
-                       else if (ret < 0) {
-                               printf("Process found but you aren't allowed to control it\n");
-                       }
-                       else {
-                               pid = ret;
-                       }
+
+               //cpu actual usage of process (range 0-1)
+               float pcpu=cu.pcpu;
+               //rate at which we are keeping active the process (range 0-1)
+               float workingrate=cu.workingrate;
+
+               //adjust work and sleep time slices
+               if (pcpu>0) {
+                       twork.tv_nsec=min(period*limit*1000/pcpu*workingrate,period*1000);
+               }
+               else if (pcpu==0) {
+                       twork.tv_nsec=period*1000;
                }
-               if (ret > 0) {
-                       if (ret == cpulimit_pid) {
-                               printf("Process %d is cpulimit itself! Aborting to avoid deadlock\n", ret);
-                               exit(1);
+               else if (pcpu==-1) {
+                       //not yet a valid idea of cpu usage
+                       pcpu=limit;
+                       workingrate=limit;
+                       twork.tv_nsec=min(period*limit*1000,period*1000);
+               }
+               tsleep.tv_nsec=period*1000-twork.tv_nsec;
+
+               //update average usage
+               pcpu_avg=(pcpu_avg*i+pcpu)/(i+1);
+
+               if (verbose && i%10==0 && i>0) {
+                       printf("%0.2f%%\t%6ld us\t%6ld us\t%0.2f%%\n",pcpu*100,twork.tv_nsec/1000,tsleep.tv_nsec/1000,workingrate*100);
+               }
+
+               if (limit<1 && limit>0) {
+                       //resume process
+                       if (kill(pid,SIGCONT)!=0) {
+                               fprintf(stderr,"Process %d dead!\n",pid);
+                               if (lazy) exit(2);
+                               //wait until our process appears
+                               goto wait_for_process;
                        }
-                       printf("Process %d found\n", pid);
-                       //control
-                       limit_process(pid, limit);
                }
-               if (lazy) {
-                       printf("Giving up...\n");
-                       break;
+
+               clock_gettime(CLOCK_REALTIME,&startwork);
+               nanosleep(&twork,NULL);         //now process is working        
+               clock_gettime(CLOCK_REALTIME,&endwork);
+               workingtime=timediff(&endwork,&startwork);
+
+               if (limit<1) {
+                       //stop process, it has worked enough
+                       if (kill(pid,SIGSTOP)!=0) {
+                               fprintf(stderr,"Process %d dead!\n",pid);
+                               if (lazy) exit(2);
+                               //wait until our process appears
+                               goto wait_for_process;
+                       }
+                       nanosleep(&tsleep,NULL);        //now process is sleeping
                }
-               sleep(2);
+               i++;
        }
-       
-       return 0;
-}
 
+}