From 120827284e3753982e493af8b1c48577e223260c Mon Sep 17 00:00:00 2001
From: Ken Thompson <ken@golang.org>
Date: Sat, 26 Jul 2008 14:21:21 -0700
Subject: [PATCH] select/chan

R=r
DELTA=517  (137 added, 98 deleted, 282 changed)
OCL=13495
CL=13495
---
 src/cmd/gc/sys.go      |   2 +-
 src/cmd/gc/sysimport.c | 335 +++++++++++++++---------------
 src/cmd/gc/walk.c      |  15 +-
 src/runtime/chan.c     | 451 ++++++++++++++++++++++-------------------
 4 files changed, 421 insertions(+), 382 deletions(-)

diff --git a/src/cmd/gc/sys.go b/src/cmd/gc/sys.go
index 502d44914b3..8c52d9e154a 100644
--- a/src/cmd/gc/sys.go
+++ b/src/cmd/gc/sys.go
@@ -47,7 +47,7 @@ func	mapassign2(hmap *map[any]any, key any, val any, pres bool);
 func	newchan(elemsize uint32, elemalg uint32, hint uint32) (hchan *chan any);
 func	chanrecv1(hchan *chan any) (elem any);
 func	chanrecv2(hchan *chan any) (elem any, pres bool);
-func	chanrecv3(hchan *chan any) (elem any, pres bool);
+func	chanrecv3(hchan *chan any, elem *any) (pres bool);
 func	chansend1(hchan *chan any, elem any);
 func	chansend2(hchan *chan any, elem any) (pres bool);
 
diff --git a/src/cmd/gc/sysimport.c b/src/cmd/gc/sysimport.c
index 571c7e83ecb..b586559fac8 100644
--- a/src/cmd/gc/sysimport.c
+++ b/src/cmd/gc/sysimport.c
@@ -3,10 +3,10 @@ char*	sysimport =
 	"type sys._esys_002 {}\n"
 	"type sys.any 24\n"
 	"type sys._esys_003 *sys.any\n"
-	"type sys._osys_361 {_esys_359 sys._esys_003}\n"
+	"type sys._osys_372 {_esys_370 sys._esys_003}\n"
 	"type sys.uint32 6\n"
-	"type sys._isys_363 {_esys_360 sys.uint32}\n"
-	"type sys._esys_001 (sys._esys_002 sys._osys_361 sys._isys_363)\n"
+	"type sys._isys_374 {_esys_371 sys.uint32}\n"
+	"type sys._esys_001 (sys._esys_002 sys._osys_372 sys._isys_374)\n"
 	"var !sys.mal sys._esys_001\n"
 	"type sys._esys_005 {}\n"
 	"type sys._esys_006 {}\n"
@@ -16,282 +16,283 @@ char*	sysimport =
 	"type sys._esys_009 {}\n"
 	"type sys._esys_010 {}\n"
 	"type sys.int32 5\n"
-	"type sys._isys_369 {_esys_368 sys.int32}\n"
-	"type sys._esys_008 (sys._esys_009 sys._esys_010 sys._isys_369)\n"
+	"type sys._isys_380 {_esys_379 sys.int32}\n"
+	"type sys._esys_008 (sys._esys_009 sys._esys_010 sys._isys_380)\n"
 	"var !sys.panicl sys._esys_008\n"
 	"type sys._esys_012 {}\n"
 	"type sys._esys_013 {}\n"
 	"type sys.bool 12\n"
-	"type sys._isys_374 {_esys_373 sys.bool}\n"
-	"type sys._esys_011 (sys._esys_012 sys._esys_013 sys._isys_374)\n"
+	"type sys._isys_385 {_esys_384 sys.bool}\n"
+	"type sys._esys_011 (sys._esys_012 sys._esys_013 sys._isys_385)\n"
 	"var !sys.printbool sys._esys_011\n"
 	"type sys._esys_015 {}\n"
 	"type sys._esys_016 {}\n"
 	"type sys.float64 10\n"
-	"type sys._isys_379 {_esys_378 sys.float64}\n"
-	"type sys._esys_014 (sys._esys_015 sys._esys_016 sys._isys_379)\n"
+	"type sys._isys_390 {_esys_389 sys.float64}\n"
+	"type sys._esys_014 (sys._esys_015 sys._esys_016 sys._isys_390)\n"
 	"var !sys.printfloat sys._esys_014\n"
 	"type sys._esys_018 {}\n"
 	"type sys._esys_019 {}\n"
 	"type sys.int64 7\n"
-	"type sys._isys_384 {_esys_383 sys.int64}\n"
-	"type sys._esys_017 (sys._esys_018 sys._esys_019 sys._isys_384)\n"
+	"type sys._isys_395 {_esys_394 sys.int64}\n"
+	"type sys._esys_017 (sys._esys_018 sys._esys_019 sys._isys_395)\n"
 	"var !sys.printint sys._esys_017\n"
 	"type sys._esys_021 {}\n"
 	"type sys._esys_022 {}\n"
 	"type sys._esys_023 25\n"
 	"type sys.string *sys._esys_023\n"
-	"type sys._isys_389 {_esys_388 sys.string}\n"
-	"type sys._esys_020 (sys._esys_021 sys._esys_022 sys._isys_389)\n"
+	"type sys._isys_400 {_esys_399 sys.string}\n"
+	"type sys._esys_020 (sys._esys_021 sys._esys_022 sys._isys_400)\n"
 	"var !sys.printstring sys._esys_020\n"
 	"type sys._esys_025 {}\n"
 	"type sys._esys_026 {}\n"
 	"type sys._esys_027 *sys.any\n"
-	"type sys._isys_394 {_esys_393 sys._esys_027}\n"
-	"type sys._esys_024 (sys._esys_025 sys._esys_026 sys._isys_394)\n"
+	"type sys._isys_405 {_esys_404 sys._esys_027}\n"
+	"type sys._esys_024 (sys._esys_025 sys._esys_026 sys._isys_405)\n"
 	"var !sys.printpointer sys._esys_024\n"
 	"type sys._esys_029 {}\n"
-	"type sys._osys_401 {_esys_398 sys.string}\n"
-	"type sys._isys_403 {_esys_399 sys.string _esys_400 sys.string}\n"
-	"type sys._esys_028 (sys._esys_029 sys._osys_401 sys._isys_403)\n"
+	"type sys._osys_412 {_esys_409 sys.string}\n"
+	"type sys._isys_414 {_esys_410 sys.string _esys_411 sys.string}\n"
+	"type sys._esys_028 (sys._esys_029 sys._osys_412 sys._isys_414)\n"
 	"var !sys.catstring sys._esys_028\n"
 	"type sys._esys_031 {}\n"
-	"type sys._osys_411 {_esys_408 sys.int32}\n"
-	"type sys._isys_413 {_esys_409 sys.string _esys_410 sys.string}\n"
-	"type sys._esys_030 (sys._esys_031 sys._osys_411 sys._isys_413)\n"
+	"type sys._osys_422 {_esys_419 sys.int32}\n"
+	"type sys._isys_424 {_esys_420 sys.string _esys_421 sys.string}\n"
+	"type sys._esys_030 (sys._esys_031 sys._osys_422 sys._isys_424)\n"
 	"var !sys.cmpstring sys._esys_030\n"
 	"type sys._esys_033 {}\n"
-	"type sys._osys_422 {_esys_418 sys.string}\n"
-	"type sys._isys_424 {_esys_419 sys.string _esys_420 sys.int32 _esys_421 sys.int32}\n"
-	"type sys._esys_032 (sys._esys_033 sys._osys_422 sys._isys_424)\n"
+	"type sys._osys_433 {_esys_429 sys.string}\n"
+	"type sys._isys_435 {_esys_430 sys.string _esys_431 sys.int32 _esys_432 sys.int32}\n"
+	"type sys._esys_032 (sys._esys_033 sys._osys_433 sys._isys_435)\n"
 	"var !sys.slicestring sys._esys_032\n"
 	"type sys._esys_035 {}\n"
 	"type sys.uint8 2\n"
-	"type sys._osys_433 {_esys_430 sys.uint8}\n"
-	"type sys._isys_435 {_esys_431 sys.string _esys_432 sys.int32}\n"
-	"type sys._esys_034 (sys._esys_035 sys._osys_433 sys._isys_435)\n"
+	"type sys._osys_444 {_esys_441 sys.uint8}\n"
+	"type sys._isys_446 {_esys_442 sys.string _esys_443 sys.int32}\n"
+	"type sys._esys_034 (sys._esys_035 sys._osys_444 sys._isys_446)\n"
 	"var !sys.indexstring sys._esys_034\n"
 	"type sys._esys_037 {}\n"
-	"type sys._osys_442 {_esys_440 sys.string}\n"
-	"type sys._isys_444 {_esys_441 sys.int64}\n"
-	"type sys._esys_036 (sys._esys_037 sys._osys_442 sys._isys_444)\n"
+	"type sys._osys_453 {_esys_451 sys.string}\n"
+	"type sys._isys_455 {_esys_452 sys.int64}\n"
+	"type sys._esys_036 (sys._esys_037 sys._osys_453 sys._isys_455)\n"
 	"var !sys.intstring sys._esys_036\n"
 	"type sys._esys_039 {}\n"
-	"type sys._osys_451 {_esys_448 sys.string}\n"
+	"type sys._osys_462 {_esys_459 sys.string}\n"
 	"type sys._esys_040 *sys.uint8\n"
-	"type sys._isys_453 {_esys_449 sys._esys_040 _esys_450 sys.int32}\n"
-	"type sys._esys_038 (sys._esys_039 sys._osys_451 sys._isys_453)\n"
+	"type sys._isys_464 {_esys_460 sys._esys_040 _esys_461 sys.int32}\n"
+	"type sys._esys_038 (sys._esys_039 sys._osys_462 sys._isys_464)\n"
 	"var !sys.byteastring sys._esys_038\n"
 	"type sys._esys_042 {}\n"
 	"type sys._esys_043 <>\n"
-	"type sys._osys_462 {_esys_458 sys._esys_043}\n"
+	"type sys._osys_473 {_esys_469 sys._esys_043}\n"
 	"type sys._esys_044 *sys.uint8\n"
 	"type sys._esys_045 *sys.uint8\n"
-	"type sys._ssys_469 {}\n"
-	"type sys._esys_046 *sys._ssys_469\n"
-	"type sys._isys_464 {_esys_459 sys._esys_044 _esys_460 sys._esys_045 _esys_461 sys._esys_046}\n"
-	"type sys._esys_041 (sys._esys_042 sys._osys_462 sys._isys_464)\n"
+	"type sys._ssys_480 {}\n"
+	"type sys._esys_046 *sys._ssys_480\n"
+	"type sys._isys_475 {_esys_470 sys._esys_044 _esys_471 sys._esys_045 _esys_472 sys._esys_046}\n"
+	"type sys._esys_041 (sys._esys_042 sys._osys_473 sys._isys_475)\n"
 	"var !sys.mkiface sys._esys_041\n"
 	"type sys._esys_048 {}\n"
-	"type sys._osys_473 {_esys_472 sys.int32}\n"
+	"type sys._osys_484 {_esys_483 sys.int32}\n"
 	"type sys._esys_049 {}\n"
-	"type sys._esys_047 (sys._esys_048 sys._osys_473 sys._esys_049)\n"
+	"type sys._esys_047 (sys._esys_048 sys._osys_484 sys._esys_049)\n"
 	"var !sys.argc sys._esys_047\n"
 	"type sys._esys_051 {}\n"
-	"type sys._osys_477 {_esys_476 sys.int32}\n"
+	"type sys._osys_488 {_esys_487 sys.int32}\n"
 	"type sys._esys_052 {}\n"
-	"type sys._esys_050 (sys._esys_051 sys._osys_477 sys._esys_052)\n"
+	"type sys._esys_050 (sys._esys_051 sys._osys_488 sys._esys_052)\n"
 	"var !sys.envc sys._esys_050\n"
 	"type sys._esys_054 {}\n"
-	"type sys._osys_482 {_esys_480 sys.string}\n"
-	"type sys._isys_484 {_esys_481 sys.int32}\n"
-	"type sys._esys_053 (sys._esys_054 sys._osys_482 sys._isys_484)\n"
+	"type sys._osys_493 {_esys_491 sys.string}\n"
+	"type sys._isys_495 {_esys_492 sys.int32}\n"
+	"type sys._esys_053 (sys._esys_054 sys._osys_493 sys._isys_495)\n"
 	"var !sys.argv sys._esys_053\n"
 	"type sys._esys_056 {}\n"
-	"type sys._osys_490 {_esys_488 sys.string}\n"
-	"type sys._isys_492 {_esys_489 sys.int32}\n"
-	"type sys._esys_055 (sys._esys_056 sys._osys_490 sys._isys_492)\n"
+	"type sys._osys_501 {_esys_499 sys.string}\n"
+	"type sys._isys_503 {_esys_500 sys.int32}\n"
+	"type sys._esys_055 (sys._esys_056 sys._osys_501 sys._isys_503)\n"
 	"var !sys.envv sys._esys_055\n"
 	"type sys._esys_058 {}\n"
-	"type sys._osys_499 {_esys_496 sys.float64 _esys_497 sys.int32}\n"
-	"type sys._isys_501 {_esys_498 sys.float64}\n"
-	"type sys._esys_057 (sys._esys_058 sys._osys_499 sys._isys_501)\n"
+	"type sys._osys_510 {_esys_507 sys.float64 _esys_508 sys.int32}\n"
+	"type sys._isys_512 {_esys_509 sys.float64}\n"
+	"type sys._esys_057 (sys._esys_058 sys._osys_510 sys._isys_512)\n"
 	"var !sys.frexp sys._esys_057\n"
 	"type sys._esys_060 {}\n"
-	"type sys._osys_508 {_esys_505 sys.float64}\n"
-	"type sys._isys_510 {_esys_506 sys.float64 _esys_507 sys.int32}\n"
-	"type sys._esys_059 (sys._esys_060 sys._osys_508 sys._isys_510)\n"
+	"type sys._osys_519 {_esys_516 sys.float64}\n"
+	"type sys._isys_521 {_esys_517 sys.float64 _esys_518 sys.int32}\n"
+	"type sys._esys_059 (sys._esys_060 sys._osys_519 sys._isys_521)\n"
 	"var !sys.ldexp sys._esys_059\n"
 	"type sys._esys_062 {}\n"
-	"type sys._osys_518 {_esys_515 sys.float64 _esys_516 sys.float64}\n"
-	"type sys._isys_520 {_esys_517 sys.float64}\n"
-	"type sys._esys_061 (sys._esys_062 sys._osys_518 sys._isys_520)\n"
+	"type sys._osys_529 {_esys_526 sys.float64 _esys_527 sys.float64}\n"
+	"type sys._isys_531 {_esys_528 sys.float64}\n"
+	"type sys._esys_061 (sys._esys_062 sys._osys_529 sys._isys_531)\n"
 	"var !sys.modf sys._esys_061\n"
 	"type sys._esys_064 {}\n"
-	"type sys._osys_527 {_esys_524 sys.bool}\n"
-	"type sys._isys_529 {_esys_525 sys.float64 _esys_526 sys.int32}\n"
-	"type sys._esys_063 (sys._esys_064 sys._osys_527 sys._isys_529)\n"
+	"type sys._osys_538 {_esys_535 sys.bool}\n"
+	"type sys._isys_540 {_esys_536 sys.float64 _esys_537 sys.int32}\n"
+	"type sys._esys_063 (sys._esys_064 sys._osys_538 sys._isys_540)\n"
 	"var !sys.isInf sys._esys_063\n"
 	"type sys._esys_066 {}\n"
-	"type sys._osys_536 {_esys_534 sys.bool}\n"
-	"type sys._isys_538 {_esys_535 sys.float64}\n"
-	"type sys._esys_065 (sys._esys_066 sys._osys_536 sys._isys_538)\n"
+	"type sys._osys_547 {_esys_545 sys.bool}\n"
+	"type sys._isys_549 {_esys_546 sys.float64}\n"
+	"type sys._esys_065 (sys._esys_066 sys._osys_547 sys._isys_549)\n"
 	"var !sys.isNaN sys._esys_065\n"
 	"type sys._esys_068 {}\n"
-	"type sys._osys_544 {_esys_542 sys.float64}\n"
-	"type sys._isys_546 {_esys_543 sys.int32}\n"
-	"type sys._esys_067 (sys._esys_068 sys._osys_544 sys._isys_546)\n"
+	"type sys._osys_555 {_esys_553 sys.float64}\n"
+	"type sys._isys_557 {_esys_554 sys.int32}\n"
+	"type sys._esys_067 (sys._esys_068 sys._osys_555 sys._isys_557)\n"
 	"var !sys.Inf sys._esys_067\n"
 	"type sys._esys_070 {}\n"
-	"type sys._osys_551 {_esys_550 sys.float64}\n"
+	"type sys._osys_562 {_esys_561 sys.float64}\n"
 	"type sys._esys_071 {}\n"
-	"type sys._esys_069 (sys._esys_070 sys._osys_551 sys._esys_071)\n"
+	"type sys._esys_069 (sys._esys_070 sys._osys_562 sys._esys_071)\n"
 	"var !sys.NaN sys._esys_069\n"
 	"type sys._esys_073 {}\n"
 	"type sys._esys_075 [sys.any] sys.any\n"
 	"type sys._esys_074 *sys._esys_075\n"
-	"type sys._osys_554 {hmap sys._esys_074}\n"
-	"type sys._isys_556 {keysize sys.uint32 valsize sys.uint32 keyalg sys.uint32 valalg sys.uint32 hint sys.uint32}\n"
-	"type sys._esys_072 (sys._esys_073 sys._osys_554 sys._isys_556)\n"
+	"type sys._osys_565 {hmap sys._esys_074}\n"
+	"type sys._isys_567 {keysize sys.uint32 valsize sys.uint32 keyalg sys.uint32 valalg sys.uint32 hint sys.uint32}\n"
+	"type sys._esys_072 (sys._esys_073 sys._osys_565 sys._isys_567)\n"
 	"var !sys.newmap sys._esys_072\n"
 	"type sys._esys_077 {}\n"
-	"type sys._osys_565 {val sys.any}\n"
+	"type sys._osys_576 {val sys.any}\n"
 	"type sys._esys_079 [sys.any] sys.any\n"
 	"type sys._esys_078 *sys._esys_079\n"
-	"type sys._isys_567 {hmap sys._esys_078 key sys.any}\n"
-	"type sys._esys_076 (sys._esys_077 sys._osys_565 sys._isys_567)\n"
+	"type sys._isys_578 {hmap sys._esys_078 key sys.any}\n"
+	"type sys._esys_076 (sys._esys_077 sys._osys_576 sys._isys_578)\n"
 	"var !sys.mapaccess1 sys._esys_076\n"
 	"type sys._esys_081 {}\n"
-	"type sys._osys_573 {val sys.any pres sys.bool}\n"
+	"type sys._osys_584 {val sys.any pres sys.bool}\n"
 	"type sys._esys_083 [sys.any] sys.any\n"
 	"type sys._esys_082 *sys._esys_083\n"
-	"type sys._isys_575 {hmap sys._esys_082 key sys.any}\n"
-	"type sys._esys_080 (sys._esys_081 sys._osys_573 sys._isys_575)\n"
+	"type sys._isys_586 {hmap sys._esys_082 key sys.any}\n"
+	"type sys._esys_080 (sys._esys_081 sys._osys_584 sys._isys_586)\n"
 	"var !sys.mapaccess2 sys._esys_080\n"
 	"type sys._esys_085 {}\n"
 	"type sys._esys_086 {}\n"
 	"type sys._esys_088 [sys.any] sys.any\n"
 	"type sys._esys_087 *sys._esys_088\n"
-	"type sys._isys_582 {hmap sys._esys_087 key sys.any val sys.any}\n"
-	"type sys._esys_084 (sys._esys_085 sys._esys_086 sys._isys_582)\n"
+	"type sys._isys_593 {hmap sys._esys_087 key sys.any val sys.any}\n"
+	"type sys._esys_084 (sys._esys_085 sys._esys_086 sys._isys_593)\n"
 	"var !sys.mapassign1 sys._esys_084\n"
 	"type sys._esys_090 {}\n"
 	"type sys._esys_091 {}\n"
 	"type sys._esys_093 [sys.any] sys.any\n"
 	"type sys._esys_092 *sys._esys_093\n"
-	"type sys._isys_588 {hmap sys._esys_092 key sys.any val sys.any pres sys.bool}\n"
-	"type sys._esys_089 (sys._esys_090 sys._esys_091 sys._isys_588)\n"
+	"type sys._isys_599 {hmap sys._esys_092 key sys.any val sys.any pres sys.bool}\n"
+	"type sys._esys_089 (sys._esys_090 sys._esys_091 sys._isys_599)\n"
 	"var !sys.mapassign2 sys._esys_089\n"
 	"type sys._esys_095 {}\n"
 	"type sys._esys_097 1 sys.any\n"
 	"type sys._esys_096 *sys._esys_097\n"
-	"type sys._osys_595 {hchan sys._esys_096}\n"
-	"type sys._isys_597 {elemsize sys.uint32 elemalg sys.uint32 hint sys.uint32}\n"
-	"type sys._esys_094 (sys._esys_095 sys._osys_595 sys._isys_597)\n"
+	"type sys._osys_606 {hchan sys._esys_096}\n"
+	"type sys._isys_608 {elemsize sys.uint32 elemalg sys.uint32 hint sys.uint32}\n"
+	"type sys._esys_094 (sys._esys_095 sys._osys_606 sys._isys_608)\n"
 	"var !sys.newchan sys._esys_094\n"
 	"type sys._esys_099 {}\n"
-	"type sys._osys_604 {elem sys.any}\n"
+	"type sys._osys_615 {elem sys.any}\n"
 	"type sys._esys_101 1 sys.any\n"
 	"type sys._esys_100 *sys._esys_101\n"
-	"type sys._isys_606 {hchan sys._esys_100}\n"
-	"type sys._esys_098 (sys._esys_099 sys._osys_604 sys._isys_606)\n"
+	"type sys._isys_617 {hchan sys._esys_100}\n"
+	"type sys._esys_098 (sys._esys_099 sys._osys_615 sys._isys_617)\n"
 	"var !sys.chanrecv1 sys._esys_098\n"
 	"type sys._esys_103 {}\n"
-	"type sys._osys_611 {elem sys.any pres sys.bool}\n"
+	"type sys._osys_622 {elem sys.any pres sys.bool}\n"
 	"type sys._esys_105 1 sys.any\n"
 	"type sys._esys_104 *sys._esys_105\n"
-	"type sys._isys_613 {hchan sys._esys_104}\n"
-	"type sys._esys_102 (sys._esys_103 sys._osys_611 sys._isys_613)\n"
+	"type sys._isys_624 {hchan sys._esys_104}\n"
+	"type sys._esys_102 (sys._esys_103 sys._osys_622 sys._isys_624)\n"
 	"var !sys.chanrecv2 sys._esys_102\n"
 	"type sys._esys_107 {}\n"
-	"type sys._osys_619 {elem sys.any pres sys.bool}\n"
+	"type sys._osys_630 {pres sys.bool}\n"
 	"type sys._esys_109 1 sys.any\n"
 	"type sys._esys_108 *sys._esys_109\n"
-	"type sys._isys_621 {hchan sys._esys_108}\n"
-	"type sys._esys_106 (sys._esys_107 sys._osys_619 sys._isys_621)\n"
+	"type sys._esys_110 *sys.any\n"
+	"type sys._isys_632 {hchan sys._esys_108 elem sys._esys_110}\n"
+	"type sys._esys_106 (sys._esys_107 sys._osys_630 sys._isys_632)\n"
 	"var !sys.chanrecv3 sys._esys_106\n"
-	"type sys._esys_111 {}\n"
 	"type sys._esys_112 {}\n"
-	"type sys._esys_114 1 sys.any\n"
-	"type sys._esys_113 *sys._esys_114\n"
-	"type sys._isys_627 {hchan sys._esys_113 elem sys.any}\n"
-	"type sys._esys_110 (sys._esys_111 sys._esys_112 sys._isys_627)\n"
-	"var !sys.chansend1 sys._esys_110\n"
-	"type sys._esys_116 {}\n"
-	"type sys._osys_632 {pres sys.bool}\n"
-	"type sys._esys_118 1 sys.any\n"
-	"type sys._esys_117 *sys._esys_118\n"
-	"type sys._isys_634 {hchan sys._esys_117 elem sys.any}\n"
-	"type sys._esys_115 (sys._esys_116 sys._osys_632 sys._isys_634)\n"
-	"var !sys.chansend2 sys._esys_115\n"
-	"type sys._esys_120 {}\n"
-	"type sys._esys_121 *sys.uint8\n"
-	"type sys._osys_640 {sel sys._esys_121}\n"
-	"type sys._isys_642 {size sys.uint32}\n"
-	"type sys._esys_119 (sys._esys_120 sys._osys_640 sys._isys_642)\n"
-	"var !sys.newselect sys._esys_119\n"
-	"type sys._esys_123 {}\n"
-	"type sys._osys_647 {selected sys.bool}\n"
-	"type sys._esys_124 *sys.uint8\n"
-	"type sys._esys_126 1 sys.any\n"
-	"type sys._esys_125 *sys._esys_126\n"
-	"type sys._isys_649 {sel sys._esys_124 hchan sys._esys_125 elem sys.any}\n"
-	"type sys._esys_122 (sys._esys_123 sys._osys_647 sys._isys_649)\n"
-	"var !sys.selectsend sys._esys_122\n"
-	"type sys._esys_128 {}\n"
-	"type sys._osys_656 {selected sys.bool}\n"
-	"type sys._esys_129 *sys.uint8\n"
-	"type sys._esys_131 1 sys.any\n"
-	"type sys._esys_130 *sys._esys_131\n"
-	"type sys._esys_132 *sys.any\n"
-	"type sys._isys_658 {sel sys._esys_129 hchan sys._esys_130 elem sys._esys_132}\n"
-	"type sys._esys_127 (sys._esys_128 sys._osys_656 sys._isys_658)\n"
-	"var !sys.selectrecv sys._esys_127\n"
-	"type sys._esys_134 {}\n"
+	"type sys._esys_113 {}\n"
+	"type sys._esys_115 1 sys.any\n"
+	"type sys._esys_114 *sys._esys_115\n"
+	"type sys._isys_638 {hchan sys._esys_114 elem sys.any}\n"
+	"type sys._esys_111 (sys._esys_112 sys._esys_113 sys._isys_638)\n"
+	"var !sys.chansend1 sys._esys_111\n"
+	"type sys._esys_117 {}\n"
+	"type sys._osys_643 {pres sys.bool}\n"
+	"type sys._esys_119 1 sys.any\n"
+	"type sys._esys_118 *sys._esys_119\n"
+	"type sys._isys_645 {hchan sys._esys_118 elem sys.any}\n"
+	"type sys._esys_116 (sys._esys_117 sys._osys_643 sys._isys_645)\n"
+	"var !sys.chansend2 sys._esys_116\n"
+	"type sys._esys_121 {}\n"
+	"type sys._esys_122 *sys.uint8\n"
+	"type sys._osys_651 {sel sys._esys_122}\n"
+	"type sys._isys_653 {size sys.uint32}\n"
+	"type sys._esys_120 (sys._esys_121 sys._osys_651 sys._isys_653)\n"
+	"var !sys.newselect sys._esys_120\n"
+	"type sys._esys_124 {}\n"
+	"type sys._osys_658 {selected sys.bool}\n"
+	"type sys._esys_125 *sys.uint8\n"
+	"type sys._esys_127 1 sys.any\n"
+	"type sys._esys_126 *sys._esys_127\n"
+	"type sys._isys_660 {sel sys._esys_125 hchan sys._esys_126 elem sys.any}\n"
+	"type sys._esys_123 (sys._esys_124 sys._osys_658 sys._isys_660)\n"
+	"var !sys.selectsend sys._esys_123\n"
+	"type sys._esys_129 {}\n"
+	"type sys._osys_667 {selected sys.bool}\n"
+	"type sys._esys_130 *sys.uint8\n"
+	"type sys._esys_132 1 sys.any\n"
+	"type sys._esys_131 *sys._esys_132\n"
+	"type sys._esys_133 *sys.any\n"
+	"type sys._isys_669 {sel sys._esys_130 hchan sys._esys_131 elem sys._esys_133}\n"
+	"type sys._esys_128 (sys._esys_129 sys._osys_667 sys._isys_669)\n"
+	"var !sys.selectrecv sys._esys_128\n"
 	"type sys._esys_135 {}\n"
-	"type sys._esys_136 *sys.uint8\n"
-	"type sys._isys_665 {sel sys._esys_136}\n"
-	"type sys._esys_133 (sys._esys_134 sys._esys_135 sys._isys_665)\n"
-	"var !sys.selectgo sys._esys_133\n"
-	"type sys._esys_138 {}\n"
+	"type sys._esys_136 {}\n"
+	"type sys._esys_137 *sys.uint8\n"
+	"type sys._isys_676 {sel sys._esys_137}\n"
+	"type sys._esys_134 (sys._esys_135 sys._esys_136 sys._isys_676)\n"
+	"var !sys.selectgo sys._esys_134\n"
 	"type sys._esys_139 {}\n"
 	"type sys._esys_140 {}\n"
-	"type sys._esys_137 (sys._esys_138 sys._esys_139 sys._esys_140)\n"
-	"var !sys.gosched sys._esys_137\n"
-	"type sys._esys_142 {}\n"
+	"type sys._esys_141 {}\n"
+	"type sys._esys_138 (sys._esys_139 sys._esys_140 sys._esys_141)\n"
+	"var !sys.gosched sys._esys_138\n"
 	"type sys._esys_143 {}\n"
 	"type sys._esys_144 {}\n"
-	"type sys._esys_141 (sys._esys_142 sys._esys_143 sys._esys_144)\n"
-	"var !sys.goexit sys._esys_141\n"
-	"type sys._esys_146 {}\n"
-	"type sys._osys_674 {_esys_671 sys.string _esys_672 sys.bool}\n"
-	"type sys._isys_676 {_esys_673 sys.string}\n"
-	"type sys._esys_145 (sys._esys_146 sys._osys_674 sys._isys_676)\n"
-	"var !sys.readfile sys._esys_145\n"
-	"type sys._esys_148 {}\n"
-	"type sys._osys_683 {_esys_680 sys.bool}\n"
-	"type sys._isys_685 {_esys_681 sys.string _esys_682 sys.string}\n"
-	"type sys._esys_147 (sys._esys_148 sys._osys_683 sys._isys_685)\n"
-	"var !sys.writefile sys._esys_147\n"
-	"type sys._esys_150 {}\n"
-	"type sys._osys_695 {_esys_690 sys.int32 _esys_691 sys.int32}\n"
-	"type sys._esys_151 *sys.uint8\n"
-	"type sys._isys_697 {_esys_692 sys._esys_151 _esys_693 sys.int32 _esys_694 sys.int32}\n"
-	"type sys._esys_149 (sys._esys_150 sys._osys_695 sys._isys_697)\n"
-	"var !sys.bytestorune sys._esys_149\n"
-	"type sys._esys_153 {}\n"
-	"type sys._osys_708 {_esys_703 sys.int32 _esys_704 sys.int32}\n"
-	"type sys._isys_710 {_esys_705 sys.string _esys_706 sys.int32 _esys_707 sys.int32}\n"
-	"type sys._esys_152 (sys._esys_153 sys._osys_708 sys._isys_710)\n"
-	"var !sys.stringtorune sys._esys_152\n"
-	"type sys._esys_155 {}\n"
+	"type sys._esys_145 {}\n"
+	"type sys._esys_142 (sys._esys_143 sys._esys_144 sys._esys_145)\n"
+	"var !sys.goexit sys._esys_142\n"
+	"type sys._esys_147 {}\n"
+	"type sys._osys_685 {_esys_682 sys.string _esys_683 sys.bool}\n"
+	"type sys._isys_687 {_esys_684 sys.string}\n"
+	"type sys._esys_146 (sys._esys_147 sys._osys_685 sys._isys_687)\n"
+	"var !sys.readfile sys._esys_146\n"
+	"type sys._esys_149 {}\n"
+	"type sys._osys_694 {_esys_691 sys.bool}\n"
+	"type sys._isys_696 {_esys_692 sys.string _esys_693 sys.string}\n"
+	"type sys._esys_148 (sys._esys_149 sys._osys_694 sys._isys_696)\n"
+	"var !sys.writefile sys._esys_148\n"
+	"type sys._esys_151 {}\n"
+	"type sys._osys_706 {_esys_701 sys.int32 _esys_702 sys.int32}\n"
+	"type sys._esys_152 *sys.uint8\n"
+	"type sys._isys_708 {_esys_703 sys._esys_152 _esys_704 sys.int32 _esys_705 sys.int32}\n"
+	"type sys._esys_150 (sys._esys_151 sys._osys_706 sys._isys_708)\n"
+	"var !sys.bytestorune sys._esys_150\n"
+	"type sys._esys_154 {}\n"
+	"type sys._osys_719 {_esys_714 sys.int32 _esys_715 sys.int32}\n"
+	"type sys._isys_721 {_esys_716 sys.string _esys_717 sys.int32 _esys_718 sys.int32}\n"
+	"type sys._esys_153 (sys._esys_154 sys._osys_719 sys._isys_721)\n"
+	"var !sys.stringtorune sys._esys_153\n"
 	"type sys._esys_156 {}\n"
-	"type sys._isys_717 {_esys_716 sys.int32}\n"
-	"type sys._esys_154 (sys._esys_155 sys._esys_156 sys._isys_717)\n"
-	"var !sys.exit sys._esys_154\n"
-	"type sys._esys_158 {}\n"
+	"type sys._esys_157 {}\n"
+	"type sys._isys_728 {_esys_727 sys.int32}\n"
+	"type sys._esys_155 (sys._esys_156 sys._esys_157 sys._isys_728)\n"
+	"var !sys.exit sys._esys_155\n"
 	"type sys._esys_159 {}\n"
 	"type sys._esys_160 {}\n"
-	"type sys._esys_157 (sys._esys_158 sys._esys_159 sys._esys_160)\n"
+	"type sys._esys_161 {}\n"
+	"type sys._esys_158 (sys._esys_159 sys._esys_160 sys._esys_161)\n"
 	"))\n"
 ;
diff --git a/src/cmd/gc/walk.c b/src/cmd/gc/walk.c
index 5cabba736b2..45dc62dbbd0 100644
--- a/src/cmd/gc/walk.c
+++ b/src/cmd/gc/walk.c
@@ -1910,7 +1910,6 @@ chanop(Node *n, int top)
 			goto shape;
 
 		// chanrecv2(hchan *chan any) (elem any, pres bool);
-
 		t = fixchan(n->right->left->type);
 		if(t == T)
 			break;
@@ -1950,19 +1949,27 @@ chanop(Node *n, int top)
 		break;
 
 	recv2:
-		// chanrecv2(hchan *chan any) (elem any, pres bool);
-fatal("recv2 not yet");
+		// chanrecv3(hchan *chan any, *elem any) (pres bool);
 		t = fixchan(n->right->type);
 		if(t == T)
 			break;
 
 		a = n->right;			// chan
 		r = a;
+		a = n->left;			// elem
+		if(a == N) {
+			a = nil;
+			a = nod(OLITERAL, N, N);
+			a->val.ctype = CTNIL;
+			a->val.vval = 0;
+		} else
+			a = nod(OADDR, a, N);
 
-		on = syslook("chanrecv2", 1);
+		on = syslook("chanrecv3", 1);
 
 		argtype(on, t->type);	// any-1
 		argtype(on, t->type);	// any-2
+
 		r = nod(OCALL, on, r);
 		n->right = r;
 		r = n;
diff --git a/src/runtime/chan.c b/src/runtime/chan.c
index 50a8855f1d0..9796e6c091f 100644
--- a/src/runtime/chan.c
+++ b/src/runtime/chan.c
@@ -33,8 +33,6 @@ struct	Hchan
 	uint32	elemsize;
 	uint32	dataqsiz;		// size of the circular q
 	uint32	qcount;			// total data in the q
-	uint16	eo;			// vararg of element
-	uint16	po;			// vararg of present bool
 	Alg*	elemalg;		// interface for element type
 	Link*	senddataq;		// pointer for sender
 	Link*	recvdataq;		// pointer for receiver
@@ -65,9 +63,12 @@ struct	Select
 {
 	uint16	tcase;			// total count of scase[]
 	uint16	ncase;			// currently filled scase[]
+	Select*	link;			// for freelist
 	Scase	scase[1];		// one per case
 };
 
+static	Select*	selfree[20];
+
 static	SudoG*	dequeue(WaitQ*, Hchan*);
 static	void	enqueue(WaitQ*, SudoG*);
 static	SudoG*	allocsg(Hchan*);
@@ -119,10 +120,6 @@ sys·newchan(uint32 elemsize, uint32 elemalg, uint32 hint,
 		c->dataqsiz = hint;
 	}
 
-	// these calculations are compiler dependent
-	c->eo = rnd(sizeof(c), elemsize);
-	c->po = rnd(c->eo+elemsize, 1);
-
 	ret = c;
 	FLUSH(&ret);
 
@@ -139,216 +136,205 @@ sys·newchan(uint32 elemsize, uint32 elemalg, uint32 hint,
 	}
 }
 
-// chansend1(hchan *chan any, elem any);
+/*
+ * generic single channel send/recv
+ * if the bool pointer is nil,
+ * then the full exchange will
+ * occur. if pres is not nil,
+ * then the protocol will not
+ * sleep but return if it could
+ * not complete
+ */
 void
-sys·chansend1(Hchan* c, ...)
+sendchan(Hchan *c, byte *ep, bool *pres)
 {
-	byte *ae;
-	SudoG *sgr;
-	G* gr;
+	SudoG *sg;
+	G* gp;
 
-	ae = (byte*)&c + c->eo;
 	if(debug) {
 		prints("chansend: chan=");
 		sys·printpointer(c);
 		prints("; elem=");
-		c->elemalg->print(c->elemsize, ae);
+		c->elemalg->print(c->elemsize, ep);
 		prints("\n");
 	}
+
 	if(c->dataqsiz > 0)
 		goto asynch;
 
-	sgr = dequeue(&c->recvq, c);
-	if(sgr != nil) {
-		c->elemalg->copy(c->elemsize, sgr->elem, ae);
+	sg = dequeue(&c->recvq, c);
+	if(sg != nil) {
+		if(ep != nil)
+			c->elemalg->copy(c->elemsize, sg->elem, ep);
 
-		gr = sgr->g;
-		gr->param = sgr;
-		gr->status = Grunnable;
+		gp = sg->g;
+		gp->param = sg;
+		gp->status = Grunnable;
+
+		if(pres != nil)
+			*pres = true;
 		return;
 	}
 
-	sgr = allocsg(c);
-	c->elemalg->copy(c->elemsize, sgr->elem, ae);
+	if(pres != nil) {
+		*pres = false;
+		return;
+	}
+
+	sg = allocsg(c);
+	if(ep != nil)
+		c->elemalg->copy(c->elemsize, sg->elem, ep);
+	g->param = nil;
 	g->status = Gwaiting;
-	enqueue(&c->sendq, sgr);
+	enqueue(&c->sendq, sg);
 	sys·gosched();
+
+	sg = g->param;
+	freesg(c, sg);
 	return;
 
 asynch:
 	while(c->qcount >= c->dataqsiz) {
-		sgr = allocsg(c);
+		sg = allocsg(c);
 		g->status = Gwaiting;
-		enqueue(&c->sendq, sgr);
+		enqueue(&c->sendq, sg);
 		sys·gosched();
 	}
-	c->elemalg->copy(c->elemsize, c->senddataq->elem, ae);
+	if(ep != nil)
+		c->elemalg->copy(c->elemsize, c->senddataq->elem, ep);
 	c->senddataq = c->senddataq->link;
 	c->qcount++;
-	sgr = dequeue(&c->recvq, c);
-	if(sgr != nil) {
-		gr = sgr->g;
-		freesg(c, sgr);
-		gr->status = Grunnable;
+
+	sg = dequeue(&c->recvq, c);
+	if(sg != nil) {
+		gp = sg->g;
+		freesg(c, sg);
+		gp->status = Grunnable;
 	}
 }
 
+static void
+chanrecv(Hchan* c, byte *ep, bool* pres)
+{
+	SudoG *sg;
+	G *gp;
+
+	if(debug) {
+		prints("chanrecv: chan=");
+		sys·printpointer(c);
+		prints("\n");
+	}
+
+	if(c->dataqsiz > 0)
+		goto asynch;
+
+	sg = dequeue(&c->sendq, c);
+	if(sg != nil) {
+		c->elemalg->copy(c->elemsize, ep, sg->elem);
+
+		gp = sg->g;
+		gp->param = sg;
+		gp->status = Grunnable;
+
+		if(pres != nil)
+			*pres = true;
+		return;
+	}
+
+	if(pres != nil) {
+		*pres = false;
+		return;
+	}
+		
+	sg = allocsg(c);
+	g->param = nil;
+	g->status = Gwaiting;
+	enqueue(&c->recvq, sg);
+	sys·gosched();
+
+	sg = g->param;
+	c->elemalg->copy(c->elemsize, ep, sg->elem);
+	freesg(c, sg);
+	return;
+
+asynch:
+	while(c->qcount <= 0) {
+		sg = allocsg(c);
+		g->status = Gwaiting;
+		enqueue(&c->recvq, sg);
+		sys·gosched();
+	}
+	c->elemalg->copy(c->elemsize, ep, c->recvdataq->elem);
+	c->recvdataq = c->recvdataq->link;
+	c->qcount--;
+	sg = dequeue(&c->sendq, c);
+	if(sg != nil) {
+		gp = sg->g;
+		freesg(c, sg);
+		gp->status = Grunnable;
+	}
+}
+
+// chansend1(hchan *chan any, elem any);
+void
+sys·chansend1(Hchan* c, ...)
+{
+	int32 o;
+	byte *ae;
+
+	o = rnd(sizeof(c), c->elemsize);
+	ae = (byte*)&c + o;
+	sendchan(c, ae, nil);
+}
+
 // chansend2(hchan *chan any, elem any) (pres bool);
 void
 sys·chansend2(Hchan* c, ...)
 {
+	int32 o;
 	byte *ae, *ap;
-	SudoG *sgr;
-	G *gr;
 
-	ae = (byte*)&c + c->eo;
-	ap = (byte*)&c + c->po;
+	o = rnd(sizeof(c), c->elemsize);
+	ae = (byte*)&c + o;
+	o = rnd(o+c->elemsize, 1);
+	ap = (byte*)&c + o;
 
-	if(debug) {
-		prints("chansend: chan=");
-		sys·printpointer(c);
-		prints("; elem=");
-		c->elemalg->print(c->elemsize, ae);
-		prints("\n");
-	}
-	if(c->dataqsiz > 0)
-		goto asynch;
-
-	sgr = dequeue(&c->recvq, c);
-	if(sgr != nil) {
-		gr = sgr->g;
-		c->elemalg->copy(c->elemsize, sgr->elem, ae);
-
-		gr->param = sgr;
-		gr->status = Grunnable;
-		*ap = true;
-		return;
-	}
-	*ap = false;
-	return;
-
-asynch:
-	if(c->qcount >= c->dataqsiz) {
-		*ap = false;
-		return;
-	}
-	c->elemalg->copy(c->elemsize, c->senddataq->elem, ae);
-	c->senddataq = c->senddataq->link;
-	c->qcount++;
-	sgr = dequeue(&c->recvq, c);
-	if(gr != nil) {
-		gr = sgr->g;
-		freesg(c, sgr);
-		gr->status = Grunnable;
-	}
-	*ap = true;
+	sendchan(c, ae, ap);
 }
 
 // chanrecv1(hchan *chan any) (elem any);
 void
 sys·chanrecv1(Hchan* c, ...)
 {
+	int32 o;
 	byte *ae;
-	SudoG *sgs;
-	G *gs;
 
-	ae = (byte*)&c + c->eo;
-	if(debug) {
-		prints("chanrecv1: chan=");
-		sys·printpointer(c);
-		prints("\n");
-	}
-	if(c->dataqsiz > 0)
-		goto asynch;
+	o = rnd(sizeof(c), c->elemsize);
+	ae = (byte*)&c + o;
 
-	sgs = dequeue(&c->sendq, c);
-	if(sgs != nil) {
-		c->elemalg->copy(c->elemsize, ae, sgs->elem);
-
-		gs = sgs->g;
-		gs->param = sgs;
-		gs->status = Grunnable;
-
-		freesg(c, sgs);
-		return;
-	}
-	sgs = allocsg(c);
-	g->status = Gwaiting;
-	enqueue(&c->recvq, sgs);
-	sys·gosched();
-	c->elemalg->copy(c->elemsize, ae, sgs->elem);
-	freesg(c, sgs);
-	return;
-
-asynch:
-	while(c->qcount <= 0) {
-		sgs = allocsg(c);
-		g->status = Gwaiting;
-		enqueue(&c->recvq, sgs);
-		sys·gosched();
-	}
-	c->elemalg->copy(c->elemsize, ae, c->recvdataq->elem);
-	c->recvdataq = c->recvdataq->link;
-	c->qcount--;
-	sgs = dequeue(&c->sendq, c);
-	if(gs != nil) {
-		gs = sgs->g;
-		freesg(c, sgs);
-
-		gs->status = Grunnable;
-	}
+	chanrecv(c, ae, nil);
 }
 
 // chanrecv2(hchan *chan any) (elem any, pres bool);
 void
 sys·chanrecv2(Hchan* c, ...)
 {
+	int32 o;
 	byte *ae, *ap;
-	SudoG *sgs;
-	G *gs;
 
-	ae = (byte*)&c + c->eo;
-	ap = (byte*)&c + c->po;
+	o = rnd(sizeof(c), c->elemsize);
+	ae = (byte*)&c + o;
+	o = rnd(o+c->elemsize, 1);
+	ap = (byte*)&c + o;
 
-	if(debug) {
-		prints("chanrecv2: chan=");
-		sys·printpointer(c);
-		prints("\n");
-	}
-	if(c->dataqsiz > 0)
-		goto asynch;
+	chanrecv(c, ae, ap);
+}
 
-	sgs = dequeue(&c->sendq, c);
-	if(sgs != nil) {
-		c->elemalg->copy(c->elemsize, ae, sgs->elem);
-
-		gs = sgs->g;
-		gs->param = sgs;
-		gs->status = Grunnable;
-
-		freesg(c, sgs);
-		*ap = true;
-		return;
-	}
-	*ap = false;
-	return;
-
-asynch:
-	if(c->qcount <= 0) {
-		*ap = false;
-		return;
-	}
-	c->elemalg->copy(c->elemsize, ae, c->recvdataq->elem);
-	c->recvdataq = c->recvdataq->link;
-	c->qcount--;
-	sgs = dequeue(&c->sendq, c);
-	if(sgs != nil) {
-		gs = sgs->g;
-		freesg(c, sgs);
-
-		gs->status = Grunnable;
-	}
-	*ap = true;
+// chanrecv3(hchan *chan any, elem *any) (pres bool);
+void
+sys·chanrecv3(Hchan* c, byte* ep, byte pres)
+{
+	chanrecv(c, ep, &pres);
 }
 
 // newselect(size uint32) (sel *byte);
@@ -360,7 +346,16 @@ sys·newselect(int32 size, Select *sel)
 	n = 0;
 	if(size > 1)
 		n = size-1;
-	sel = mal(sizeof(*sel) + n*sizeof(sel->scase[0]));
+
+	sel = nil;
+	if(size >= 1 && size < nelem(selfree)) {
+		sel = selfree[size];
+		if(sel != nil)
+			selfree[size] = sel->link;
+	}
+	if(sel == nil)
+		sel = mal(sizeof(*sel) + n*sizeof(sel->scase[0]));
+
 	sel->tcase = size;
 	sel->ncase = 0;
 	FLUSH(&sel);
@@ -419,7 +414,7 @@ sys·selectsend(Select *sel, Hchan *c, ...)
 void
 sys·selectrecv(Select *sel, Hchan *c, ...)
 {
-	int32 i, epo;
+	int32 i, eo;
 	Scase *cas;
 
 	// nil cases do not compete
@@ -435,11 +430,11 @@ sys·selectrecv(Select *sel, Hchan *c, ...)
 	cas->pc = sys·getcallerpc(&sel);
 	cas->chan = c;
 
-	epo = rnd(sizeof(sel), sizeof(c));
-	epo = rnd(epo+sizeof(c), sizeof(byte*));
-	cas->so = rnd(epo+sizeof(byte*), 1);
+	eo = rnd(sizeof(sel), sizeof(c));
+	eo = rnd(eo+sizeof(c), sizeof(byte*));
+	cas->so = rnd(eo+sizeof(byte*), 1);
 	cas->send = 0;
-	cas->u.elemp = *(byte**)((byte*)&sel + epo);
+	cas->u.elemp = *(byte**)((byte*)&sel + eo);
 
 	if(debug) {
 		prints("newselect s=");
@@ -456,6 +451,8 @@ sys·selectrecv(Select *sel, Hchan *c, ...)
 	}
 }
 
+uint32	xxx	= 0;
+
 // selectgo(sel *byte);
 void
 sys·selectgo(Select *sel)
@@ -468,7 +465,7 @@ sys·selectgo(Select *sel)
 
 	byte *ae, *as;
 
-	if(0) {
+	if(xxx) {
 		prints("selectgo: sel=");
 		sys·printpointer(sel);
 		prints("\n");
@@ -502,20 +499,23 @@ sys·selectgo(Select *sel)
 		c = cas->chan;
 
 		if(c->dataqsiz > 0) {
-			if(cas->send)
-				throw("selectgo: send asynch");
-			else
-				throw("selectgo: recv asynch");
+			if(cas->send) {
+				if(c->qcount < c->dataqsiz)
+					goto asyns;
+			} else {
+				if(c->qcount > 0)
+					goto asynr;
+			}
 		}
 
 		if(cas->send) {
 			sg = dequeue(&c->recvq, c);
 			if(sg != nil)
-				goto gotr;
+				goto gots;
 		} else {
 			sg = dequeue(&c->sendq, c);
 			if(sg != nil)
-				goto gots;
+				goto gotr;
 		}
 
 		o += p;
@@ -527,19 +527,39 @@ sys·selectgo(Select *sel)
 	for(i=0; i<sel->ncase; i++) {
 		cas = &sel->scase[o];
 		c = cas->chan;
+
+		if(c->dataqsiz > 0) {
+			if(cas->send) {
+				if(c->qcount < c->dataqsiz) {
+					prints("second pass asyn send\n");
+					goto asyns;
+				}
+			} else {
+				if(c->qcount > 0) {
+					prints("second pass asyn recv\n");
+					goto asynr;
+				}
+			}
+		}
+
 		if(cas->send) {
 			sg = dequeue(&c->recvq, c);
-			if(sg != nil)
-				goto gotr;	// probably an error
+			if(sg != nil) {
+				prints("second pass syn send\n");
+				g->selgen++;
+				goto gots;	// probably an error
+			}
 			sg = allocsg(c);
 			sg->offset = o;
 			c->elemalg->copy(c->elemsize, sg->elem, cas->u.elem);
 			enqueue(&c->sendq, sg);
 		} else {
 			sg = dequeue(&c->sendq, c);
-			if(sg != nil)
-				goto gots;	// probably an error
-
+			if(sg != nil) {
+				prints("second pass syn recv\n");
+				g->selgen++;
+				goto gotr;	// probably an error
+			}
 			sg = allocsg(c);
 			sg->offset = o;
 			enqueue(&c->recvq, sg);
@@ -550,56 +570,44 @@ sys·selectgo(Select *sel)
 			o -= sel->ncase;
 	}
 
-	if(0) {
-		prints("wait: sel=");
-		sys·printpointer(sel);
-		prints("\n");
-	}
+	// send and recv paths to sleep for a rendezvous
 	g->status = Gwaiting;
 	sys·gosched();
 
-	if(0) {
-		prints("wait-return: sel=");
-		sys·printpointer(sel);
-		prints("\n");
-	}
-
 	sg = g->param;
 	o = sg->offset;
 	cas = &sel->scase[o];
 	c = cas->chan;
 
-	if(0) {
-		prints("wake: sel=");
+	if(xxx) {
+		prints("wait-return: sel=");
 		sys·printpointer(sel);
 		prints(" c=");
 		sys·printpointer(c);
+		prints(" cas=");
+		sys·printpointer(cas);
+		prints(" send=");
+		sys·printint(cas->send);
 		prints(" o=");
 		sys·printint(o);
 		prints("\n");
 	}
-	if(cas->send)
-		goto gots;
 
-gotr:
-	if(0) {
-		prints("gotr: sel=");
-		sys·printpointer(sel);
-		prints(" c=");
-		sys·printpointer(c);
-		prints(" o=");
-		sys·printint(o);
-		prints("\n");
+	if(!cas->send) {
+		if(cas->u.elemp != nil)
+			c->elemalg->copy(c->elemsize, cas->u.elemp, sg->elem);
 	}
-	c->elemalg->copy(c->elemsize, sg->elem, cas->u.elem);
-	gp = sg->g;
-	gp->param = sg;
-	gp->status = Grunnable;
+
+	freesg(c, sg);
 	goto retc;
 
-gots:
-	if(0) {
-		prints("gots: sel=");
+asynr:
+asyns:
+	throw("asyn");
+gotr:
+	// recv path to wakeup the sender (sg)
+	if(xxx) {
+		prints("gotr: sel=");
 		sys·printpointer(sel);
 		prints(" c=");
 		sys·printpointer(c);
@@ -612,9 +620,30 @@ gots:
 	gp = sg->g;
 	gp->param = sg;
 	gp->status = Grunnable;
-	freesg(c, sg);
+	goto retc;
+
+gots:
+	// send path to wakeup the receiver (sg)
+	if(xxx) {
+		prints("gots: sel=");
+		sys·printpointer(sel);
+		prints(" c=");
+		sys·printpointer(c);
+		prints(" o=");
+		sys·printint(o);
+		prints("\n");
+	}
+	c->elemalg->copy(c->elemsize, sg->elem, cas->u.elem);
+	gp = sg->g;
+	gp->param = sg;
+	gp->status = Grunnable;
 
 retc:
+	if(sel->ncase >= 1 && sel->ncase < nelem(selfree)) {
+		sel->link = selfree[sel->ncase];
+		selfree[sel->ncase] = sel;
+	}
+
 	sys·setcallerpc(&sel, cas->pc);
 	as = (byte*)&sel + cas->so;
 	*as = true;
@@ -668,6 +697,8 @@ allocsg(Hchan *c)
 		sg = mal(sizeof(*sg));
 	sg->selgen = g->selgen;
 	sg->g = g;
+	sg->offset = 0;
+
 	return sg;
 }