1 c6687d45 2004-09-21 devnull /*
  2 c6687d45 2004-09-21 devnull  * This needs to be callable from a signal handler, so it has been
  3 c6687d45 2004-09-21 devnull  * written to avoid locks.  The only lock is the one used to acquire
  4 c6687d45 2004-09-21 devnull  * an entry in the table, and we make sure that acquiring is done
  5 c6687d45 2004-09-21 devnull  * when not in a handler.  Lookup and delete do not need locks.
  6 c6687d45 2004-09-21 devnull  * It's a scan-forward hash table.  To avoid breaking chains, 
  7 c6687d45 2004-09-21 devnull  * T ((void*)-1) is used as a non-breaking nil.
  8 c6687d45 2004-09-21 devnull  */
  9 c6687d45 2004-09-21 devnull 
 10 c6687d45 2004-09-21 devnull #include <u.h>
 11 c6687d45 2004-09-21 devnull #include <libc.h>
 12 c6687d45 2004-09-21 devnull #include "9proc.h"
 13 c6687d45 2004-09-21 devnull 
 14 c6687d45 2004-09-21 devnull enum { PIDHASH = 1021 };
 15 c6687d45 2004-09-21 devnull 
 16 c6687d45 2004-09-21 devnull #define T ((void*)-1)
 17 c6687d45 2004-09-21 devnull static Uproc *alluproc[PIDHASH];
 18 c6687d45 2004-09-21 devnull static int allupid[PIDHASH];
 19 c6687d45 2004-09-21 devnull static Lock uproclock;
 20 c6687d45 2004-09-21 devnull 
 21 c6687d45 2004-09-21 devnull void
 22 c6687d45 2004-09-21 devnull _clearuproc(void)
 23 c6687d45 2004-09-21 devnull {
 24 c6687d45 2004-09-21 devnull 	int i;
 25 c6687d45 2004-09-21 devnull 
 26 c6687d45 2004-09-21 devnull 	/* called right after fork - no locking needed */
 27 c6687d45 2004-09-21 devnull 	for(i=0; i<PIDHASH; i++)
 28 c6687d45 2004-09-21 devnull 		if(alluproc[i] != T && alluproc[i] != 0)
 29 c6687d45 2004-09-21 devnull 			free(alluproc[i]);
 30 c6687d45 2004-09-21 devnull 	memset(alluproc, 0, sizeof alluproc);
 31 c6687d45 2004-09-21 devnull 	memset(allupid, 0, sizeof allupid);
 32 c6687d45 2004-09-21 devnull }
 33 c6687d45 2004-09-21 devnull 		
 34 c6687d45 2004-09-21 devnull Uproc*
 35 c6687d45 2004-09-21 devnull _p9uproc(int inhandler)
 36 c6687d45 2004-09-21 devnull {
 37 c6687d45 2004-09-21 devnull 	int i, h, pid;
 38 c6687d45 2004-09-21 devnull 	Uproc *up;
 39 c6687d45 2004-09-21 devnull 
 40 c6687d45 2004-09-21 devnull 	/* for now, assume getpid is fast or cached */
 41 c6687d45 2004-09-21 devnull 	pid = getpid();
 42 c6687d45 2004-09-21 devnull 
 43 c6687d45 2004-09-21 devnull 	/*
 44 c6687d45 2004-09-21 devnull 	 * this part - the lookup - needs to run without locks
 45 c6687d45 2004-09-21 devnull 	 * so that it can safely be called from within the notify handler.
 46 c6687d45 2004-09-21 devnull 	 * notify calls _p9uproc, and fork and rfork call _p9uproc
 47 c6687d45 2004-09-21 devnull 	 * in both parent and child, so if we're in a signal handler,
 48 c6687d45 2004-09-21 devnull 	 * we should find something in the table.
 49 c6687d45 2004-09-21 devnull 	 */
 50 c6687d45 2004-09-21 devnull 	h = pid%PIDHASH;
 51 c6687d45 2004-09-21 devnull 	for(i=0; i<PIDHASH; i++){
 52 c6687d45 2004-09-21 devnull 		up = alluproc[h];
 53 c6687d45 2004-09-21 devnull 		if(up == nil)
 54 c6687d45 2004-09-21 devnull 			break;
 55 c6687d45 2004-09-21 devnull 		if(allupid[h] == pid)
 56 c6687d45 2004-09-21 devnull 			return up;
 57 c6687d45 2004-09-21 devnull 		if(++h == PIDHASH)
 58 c6687d45 2004-09-21 devnull 			h = 0;
 59 c6687d45 2004-09-21 devnull 	}
 60 c6687d45 2004-09-21 devnull 
 61 c6687d45 2004-09-21 devnull 	if(inhandler){
 62 c6687d45 2004-09-21 devnull 		fprint(2, "%s: did not find uproc for pid %d in signal handler\n", argv0, pid);
 63 c6687d45 2004-09-21 devnull 		abort();	
 64 c6687d45 2004-09-21 devnull 	}
 65 c6687d45 2004-09-21 devnull 
 66 c6687d45 2004-09-21 devnull 	/* need to allocate */
 67 c6687d45 2004-09-21 devnull 	while((up = mallocz(sizeof(Uproc), 1)) == nil)
 68 c6687d45 2004-09-21 devnull 		sleep(1000);
 69 c6687d45 2004-09-21 devnull 
 70 c6687d45 2004-09-21 devnull 	/* fprint(2, "alloc uproc for pid %d\n", pid); */
 71 c6687d45 2004-09-21 devnull 	up->pid = pid;
 72 c6687d45 2004-09-21 devnull 	lock(&uproclock);
 73 c6687d45 2004-09-21 devnull 	h = pid%PIDHASH;
 74 c6687d45 2004-09-21 devnull 	for(i=0; i<PIDHASH; i++){
 75 c6687d45 2004-09-21 devnull 		if(alluproc[h]==T || alluproc[h]==nil){
 76 c6687d45 2004-09-21 devnull 			alluproc[h] = up;
 77 c6687d45 2004-09-21 devnull 			allupid[h] = pid;
 78 c6687d45 2004-09-21 devnull 			unlock(&uproclock);
 79 c6687d45 2004-09-21 devnull 			return up;
 80 c6687d45 2004-09-21 devnull 		}
 81 c6687d45 2004-09-21 devnull 		if(++h == PIDHASH)
 82 c6687d45 2004-09-21 devnull 			h = 0;
 83 c6687d45 2004-09-21 devnull 	}
 84 c6687d45 2004-09-21 devnull 	unlock(&uproclock);
 85 c6687d45 2004-09-21 devnull 
 86 c6687d45 2004-09-21 devnull 	/* out of pids! */
 87 c6687d45 2004-09-21 devnull 	sysfatal("too many processes in uproc table");
 88 c6687d45 2004-09-21 devnull 	return nil;
 89 c6687d45 2004-09-21 devnull }
 90 c6687d45 2004-09-21 devnull 
 91 c6687d45 2004-09-21 devnull void
 92 c6687d45 2004-09-21 devnull _p9uprocdie(void)
 93 c6687d45 2004-09-21 devnull {
 94 c6687d45 2004-09-21 devnull 	Uproc *up;
 95 c6687d45 2004-09-21 devnull 	int pid, i, h;
 96 c6687d45 2004-09-21 devnull 
 97 c6687d45 2004-09-21 devnull 	pid = getpid();
 98 c6687d45 2004-09-21 devnull 	/* fprint(2, "reap uproc for pid %d\n", pid); */
 99 c6687d45 2004-09-21 devnull 	h = pid%PIDHASH;
100 c6687d45 2004-09-21 devnull 	for(i=0; i<PIDHASH; i++){
101 c6687d45 2004-09-21 devnull 		up = alluproc[h];
102 c6687d45 2004-09-21 devnull 		if(up == nil)
103 c6687d45 2004-09-21 devnull 			break;
104 c6687d45 2004-09-21 devnull 		if(up == T)
105 c6687d45 2004-09-21 devnull 			continue;
106 c6687d45 2004-09-21 devnull 		if(allupid[h] == pid){
107 c6687d45 2004-09-21 devnull 			up = alluproc[h];
108 c6687d45 2004-09-21 devnull 			alluproc[h] = T;
109 c6687d45 2004-09-21 devnull 			free(up);
110 c6687d45 2004-09-21 devnull 			allupid[h] = 0;
111 c6687d45 2004-09-21 devnull 		}
112 c6687d45 2004-09-21 devnull 	}
113 c6687d45 2004-09-21 devnull }