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/*
* This needs to be callable from a signal handler, so it has been
* written to avoid locks. The only lock is the one used to acquire
* an entry in the table, and we make sure that acquiring is done
* when not in a handler. Lookup and delete do not need locks.
* It's a scan-forward hash table. To avoid breaking chains,
* T ((void*)-1) is used as a non-breaking nil.
*/
#include <u.h>
#include <libc.h>
#include "9proc.h"
enum { PIDHASH = 1021 };
#define T ((void*)-1)
static Uproc *alluproc[PIDHASH];
static int allupid[PIDHASH];
static Lock uproclock;
Uproc*
_p9uproc(int inhandler)
{
int i, h, pid;
Uproc *up;
/* for now, assume getpid is fast or cached */
pid = getpid();
/*
* this part - the lookup - needs to run without locks
* so that it can safely be called from within the notify handler.
* notify calls _p9uproc, and fork and rfork call _p9uproc
* in both parent and child, so if we're in a signal handler,
* we should find something in the table.
*/
h = pid%PIDHASH;
for(i=0; i<PIDHASH; i++){
up = alluproc[h];
if(up == nil)
break;
if(allupid[h] == pid)
return up;
if(++h == PIDHASH)
h = 0;
}
if(inhandler)
sysfatal("did not find uproc in signal handler");
/* need to allocate */
while((up = mallocz(sizeof(Uproc), 1)) == nil)
sleep(1000);
up = mallocz(sizeof(Uproc), 1);
lock(&uproclock);
h = pid%PIDHASH;
for(i=0; i<PIDHASH; i++){
if(alluproc[h]==T || alluproc[h]==nil){
alluproc[h] = up;
allupid[h] = pid;
return up;
}
if(++h == PIDHASH)
h = 0;
}
unlock(&uproclock);
/* out of pids! */
sysfatal("too many processes in uproc table");
return nil;
}
void
_p9uprocdie(void)
{
Uproc *up;
int pid, i, h;
pid = getpid();
h = pid%PIDHASH;
for(i=0; i<PIDHASH; i++){
up = alluproc[h];
if(up == nil)
break;
if(up == T)
continue;
if(allupid[h] == pid){
up = alluproc[h];
alluproc[h] = T;
free(up);
allupid[h] = 0;
}
}
}
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