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kernel: better pidalloc()

--- a/sys/src/9/port/proc.c

+++ b/sys/src/9/port/proc.c

@@ -1592,19 +1592,22 @@

 int

 pidalloc(Proc *p)

 {

-	static Ref ref;

+	static int gen, wrapped;

 	int pid, h;

 	Proc *x;

 	lock(&procalloc);

 Retry:

-	pid = incref(&ref) & 0x7FFFFFFF;

-	if(pid == 0)

+	pid = ++gen & 0x7FFFFFFF;

+	if(pid == 0){

+		wrapped = 1;

 		goto Retry;

+	}

 	h = pid % nelem(procalloc.ht);

-	for(x = procalloc.ht[h]; x != nil; x = x->pidhash)

-		if(x->pid == pid)

-			goto Retry;

+	if(wrapped)

+		for(x = procalloc.ht[h]; x != nil; x = x->pidhash)

+			if(x->pid == pid)

+				goto Retry;

 	if(p){

 		p->pid = pid;

 		p->pidhash = procalloc.ht[h];

-- 

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