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runtime: cache gotraceback setting 

On Plan 9 gotraceback calls getenv calls malloc, and we gotraceback
on every call to gentraceback, which happens during garbage collection.
Honestly I don't even know how this works on Plan 9.
I suspect it does not, and that we are getting by because
no one has tried to run with $GOTRACEBACK set at all.

This will speed up all the other systems by epsilon, since they
won't call getenv and atoi repeatedly.

LGTM=bradfitz
R=golang-codereviews, bradfitz, 0intro
CC=golang-codereviews
https://golang.org/cl/85430046
This commit is contained in:
Russ Cox 2014-04-08 22:35:41 -04:00
parent b3a33a654d
commit 5556bfa9c7
2 changed files with 28 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
src/pkg/runtime/proc.c
View File

@ -155,6 +155,10 @@ runtime·schedinit(void)
// in a fault during a garbage collection, it will not
// need to allocated memory.
runtime·newErrorCString(0, &i);
// Initialize the cached gotraceback value, since
// gotraceback calls getenv, which mallocs on Plan 9.
runtime·gotraceback(nil);
runtime·goargs();
runtime·goenvs();

35
src/pkg/runtime/runtime.c
View File

@ -20,22 +20,35 @@ enum {
int32
runtime·gotraceback(bool *crash)
{
// Keep a cached value to make gotraceback fast,
// since we call it on every call to gentraceback.
// The cached value is a uint32 in which the low bit
// is the "crash" setting and the top 31 bits are the
// gotraceback value.
static uint32 cache = ~(uint32)0;
byte *p;
uint32 x;
if(crash != nil)
*crash = false;
p = runtime·getenv("GOTRACEBACK");
if(p == nil || p[0] == '\0') {
if(m->traceback != 0)
return m->traceback;
return 1; // default is on
if(m->traceback != 0)
return m->traceback;
x = runtime·atomicload(&cache);
if(x == ~(uint32)0) {
p = runtime·getenv("GOTRACEBACK");
if(p == nil)
p = (byte*)"";
if(p[0] == '\0')
x = 1<<1;
else if(runtime·strcmp(p, (byte*)"crash") == 0)
x = (2<<1) | 1;
else
x = runtime·atoi(p)<<1;
runtime·atomicstore(&cache, x);
}
if(runtime·strcmp(p, (byte*)"crash") == 0) {
if(crash != nil)
*crash = true;
return 2; // extra information
}
return runtime·atoi(p);
if(crash != nil)
*crash = x&1;
return x>>1;
}
int32