code review 6610064: race: syscall changes

src/pkg/syscall/syscall_plan9.go

 // Copyright 2011 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.
 
 // Plan 9 system calls.
 // This file is compiled as ordinary Go code,
 // but it is also input to mksyscall,
 // which parses the //sys lines and generates system call stubs.
 // Note that sometimes we use a lowercase //sys name and
 // wrap it in our own nicer implementation.
@@ skipping 97 matching lines @@
         n, _ := readnum("#c/pid")
         return int(n)
 }
 
 func Getppid() (ppid int) {
         n, _ := readnum("#c/ppid")
         return int(n)
 }
 
 func Read(fd int, p []byte) (n int, err error) {
-        return Pread(fd, p, -1)
+        n, err = Pread(fd, p, -1)
+        if raceenabled && err == nil {
+                raceAcquire(unsafe.Pointer(&ioSync))
+        }
+        return
 }
 
 func Write(fd int, p []byte) (n int, err error) {
+        if raceenabled {
+                raceReleaseMerge(unsafe.Pointer(&ioSync))
+        }
         return Pwrite(fd, p, -1)
 }
 
+var ioSync int64
+
 func Getwd() (wd string, err error) {
         fd, e := Open(".", O_RDONLY)
 
         if e != nil {
                 return "", e
         }
         defer Close(fd)
 
         return Fd2path(fd)
 }
@@ skipping 210 matching lines @@
 //sys   Pread(fd int, p []byte, offset int64) (n int, err error)
 //sys   Pwrite(fd int, p []byte, offset int64) (n int, err error)
 //sys   Close(fd int) (err error)
 //sys   Chdir(path string) (err error)
 //sys   Bind(name string, old string, flag int) (err error)
 //sys   Mount(fd int, afd int, old string, flag int, aname string) (err error)
 //sys   Stat(path string, edir []byte) (n int, err error)
 //sys   Fstat(fd int, edir []byte) (n int, err error)
 //sys   Wstat(path string, edir []byte) (err error)
 //sys   Fwstat(fd int, edir []byte) (err error)