| // Copyright 2010 The Go Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| #include "runtime.h" |
| #include "os_GOOS.h" |
| #include "../../cmd/ld/textflag.h" |
| |
| #pragma textflag NOSPLIT |
| int64 |
| runtime·nanotime(void) |
| { |
| static int32 fd = -1; |
| byte b[8]; |
| uint32 hi, lo; |
| |
| // As long as all goroutines share the same file |
| // descriptor table we can get away with using |
| // just a static fd. Without a lock the file can |
| // be opened twice but that's okay. |
| // |
| // Using /dev/bintime gives us a latency on the |
| // order of ten microseconds between two calls. |
| // |
| // The naïve implementation (without the cached |
| // file descriptor) is roughly four times slower |
| // in 9vx on a 2.16 GHz Intel Core 2 Duo. |
| |
| if(fd < 0 && (fd = runtime·open("/dev/bintime", OREAD|OCEXEC, 0)) < 0) |
| return 0; |
| if(runtime·pread(fd, b, sizeof b, 0) != sizeof b) |
| return 0; |
| hi = b[0]<<24 | b[1]<<16 | b[2]<<8 | b[3]; |
| lo = b[4]<<24 | b[5]<<16 | b[6]<<8 | b[7]; |
| return (int64)hi<<32 | (int64)lo; |
| } |
