[go-nuts] Why file write in routine can not be read outside?

Davy zhang

at Mar 7, 2013 at 5:45 am

but when I put

time.Sleep(1 * time.Second)

after the

<-time.Tick(2 * time.Second)

the file can be read after that, so is there explanation ?

On Thursday, March 7, 2013 1:42:21 PM UTC+8, davy zhang wrote:

code first
http://play.golang.org/p/YldOJZNg1a

its been report written 2 times, but after 2 seconds tick the main
function can not read the content of the file

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Davy zhang

at Mar 7, 2013 at 5:57 am

⇧

I used sync and os.O_SYNC

http://play.golang.org/p/q5SA0eV2pi

but the result is the same

but when manually open the file using less /tmp/filesave

the content is there! So the file is written actually but the problem is
the way I read it?

On Thursday, March 7, 2013 1:45:00 PM UTC+8, davy zhang wrote:

but when I put

time.Sleep(1 * time.Second)

after the

<-time.Tick(2 * time.Second)

the file can be read after that, so is there explanation ?

On Thursday, March 7, 2013 1:42:21 PM UTC+8, davy zhang wrote:

code first
http://play.golang.org/p/YldOJZNg1a

its been report written 2 times, but after 2 seconds tick the main
function can not read the content of the file

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Tamás Gulácsi

at Mar 7, 2013 at 6:14 am

⇧

It works for me
gthomas@waterhouse /tmp % go test -v x_test.go
warning: building out-of-date packages:
flag
text/tabwriter
runtime/pprof
testing
installing these packages with 'go test -i x_test.go' will speed future
tests.

=== RUN TestStoreFileSave
updated value 12345789 /tmp/filesave
written 8
updated value 12345789 /tmp/filesave
written 8
12345789
--- PASS: TestStoreFileSave (2.00 seconds)
PASS
ok command-line-arguments 2.018s

gthomas@waterhouse /tmp % go version
go version devel +08dc15884e88 Mon Feb 25 08:29:46 2013 -0800 linux/amd64

GThomas

2013. március 7., csütörtök 6:57:36 UTC+1 időpontban davy zhang a
következőt írta:

I used sync and os.O_SYNC

http://play.golang.org/p/q5SA0eV2pi

but the result is the same

but when manually open the file using less /tmp/filesave

the content is there! So the file is written actually but the problem is
the way I read it?

On Thursday, March 7, 2013 1:45:00 PM UTC+8, davy zhang wrote:

but when I put

time.Sleep(1 * time.Second)

after the

<-time.Tick(2 * time.Second)

the file can be read after that, so is there explanation ?

On Thursday, March 7, 2013 1:42:21 PM UTC+8, davy zhang wrote:

code first
http://play.golang.org/p/YldOJZNg1a

its been report written 2 times, but after 2 seconds tick the main
function can not read the content of the file

--
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Davy zhang

at Mar 7, 2013 at 6:16 am

⇧

I am using the stable version is that the main reason ?

go version go1.0.3

On Thursday, March 7, 2013 2:14:19 PM UTC+8, Tamás Gulácsi wrote:

It works for me
gthomas@waterhouse /tmp % go test -v x_test.go
warning: building out-of-date packages:
flag
text/tabwriter
runtime/pprof
testing
installing these packages with 'go test -i x_test.go' will speed future
tests.

=== RUN TestStoreFileSave
updated value 12345789 /tmp/filesave
written 8
updated value 12345789 /tmp/filesave
written 8
12345789
--- PASS: TestStoreFileSave (2.00 seconds)
PASS
ok command-line-arguments 2.018s

gthomas@waterhouse /tmp % go version
go version devel +08dc15884e88 Mon Feb 25 08:29:46 2013 -0800 linux/amd64

GThomas

2013. március 7., csütörtök 6:57:36 UTC+1 időpontban davy zhang a
következőt írta:

I used sync and os.O_SYNC

http://play.golang.org/p/q5SA0eV2pi

but the result is the same

but when manually open the file using less /tmp/filesave

the content is there! So the file is written actually but the problem is
the way I read it?

On Thursday, March 7, 2013 1:45:00 PM UTC+8, davy zhang wrote:

but when I put

time.Sleep(1 * time.Second)

after the

<-time.Tick(2 * time.Second)

the file can be read after that, so is there explanation ?

On Thursday, March 7, 2013 1:42:21 PM UTC+8, davy zhang wrote:

code first
http://play.golang.org/p/YldOJZNg1a

its been report written 2 times, but after 2 seconds tick the main
function can not read the content of the file

--
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Davy zhang

at Mar 7, 2013 at 6:25 am

⇧

Thanks for the test, but could you run few more times? This test sometimes
is right, but not always. Thanks again.

On Thu, Mar 7, 2013 at 2:14 PM, Tamás Gulácsi wrote:

It works for me
gthomas@waterhouse /tmp % go test -v x_test.go
warning: building out-of-date packages:
flag
text/tabwriter
runtime/pprof
testing
installing these packages with 'go test -i x_test.go' will speed future
tests.

=== RUN TestStoreFileSave
updated value 12345789 /tmp/filesave
written 8
updated value 12345789 /tmp/filesave
written 8
12345789
--- PASS: TestStoreFileSave (2.00 seconds)
PASS
ok command-line-arguments 2.018s

gthomas@waterhouse /tmp % go version
go version devel +08dc15884e88 Mon Feb 25 08:29:46 2013 -0800 linux/amd64

GThomas

2013. március 7., csütörtök 6:57:36 UTC+1 időpontban davy zhang a
következőt írta:

I used sync and os.O_SYNC

http://play.golang.org/p/**q5SA0eV2pi<http://play.golang.org/p/q5SA0eV2pi>

but the result is the same

but when manually open the file using less /tmp/filesave

the content is there! So the file is written actually but the problem is
the way I read it?

On Thursday, March 7, 2013 1:45:00 PM UTC+8, davy zhang wrote:

but when I put

time.Sleep(1 * time.Second)

after the

<-time.Tick(2 * time.Second)

the file can be read after that, so is there explanation ?

On Thursday, March 7, 2013 1:42:21 PM UTC+8, davy zhang wrote:

code first
http://play.golang.org/p/**YldOJZNg1a<http://play.golang.org/p/YldOJZNg1a>

its been report written 2 times, but after 2 seconds tick the main
function can not read the content of the file

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Davy zhang

at Mar 7, 2013 at 7:04 am

⇧

I tested using
go version devel +131f8c8eb722 Wed Mar 06 16:52:03 2013 -0800 darwin/amd64

and there's no real improvement, it did printed the content at first time
but after that, the result is unstable, sometimes right, sometimes nothing
printed

On Thursday, March 7, 2013 2:25:20 PM UTC+8, davy zhang wrote:

Thanks for the test, but could you run few more times? This test sometimes
is right, but not always. Thanks again.

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Gulácsi Tamás

at Mar 7, 2013 at 7:24 am

⇧

Works consistently.
Just for the record, my /tmp is a tmpfs...

Questions:
1. why do you open the file with truncating in each goroutine, and not
close the file handler at the end?
2. why don't you synchronize betweem the trunncates and the read? If you
read just when the goroutine opens (ant truncates) the file, than you will
read zero length.
3. what do you test here? Two instances of time.Tick don't happen at once.

GThomas

2013/3/7 davy zhang <davyzhang@gmail.com>

Thanks for the test, but could you run few more times? This test sometimes
is right, but not always. Thanks again.

On Thu, Mar 7, 2013 at 2:14 PM, Tamás Gulácsi wrote:

It works for me
gthomas@waterhouse /tmp % go test -v x_test.go
warning: building out-of-date packages:
flag
text/tabwriter
runtime/pprof
testing
installing these packages with 'go test -i x_test.go' will speed future
tests.

=== RUN TestStoreFileSave
updated value 12345789 /tmp/filesave
written 8
updated value 12345789 /tmp/filesave
written 8
12345789
--- PASS: TestStoreFileSave (2.00 seconds)
PASS
ok command-line-arguments 2.018s

gthomas@waterhouse /tmp % go version
go version devel +08dc15884e88 Mon Feb 25 08:29:46 2013 -0800 linux/amd64

GThomas

2013. március 7., csütörtök 6:57:36 UTC+1 időpontban davy zhang a
következőt írta:

I used sync and os.O_SYNC

http://play.golang.org/p/**q5SA0eV2pi<http://play.golang.org/p/q5SA0eV2pi>

but the result is the same

but when manually open the file using less /tmp/filesave

the content is there! So the file is written actually but the problem is
the way I read it?

On Thursday, March 7, 2013 1:45:00 PM UTC+8, davy zhang wrote:

but when I put

time.Sleep(1 * time.Second)

after the

<-time.Tick(2 * time.Second)

the file can be read after that, so is there explanation ?

On Thursday, March 7, 2013 1:42:21 PM UTC+8, davy zhang wrote:

code first
http://play.golang.org/p/**YldOJZNg1a<http://play.golang.org/p/YldOJZNg1a>

its been report written 2 times, but after 2 seconds tick the main
function can not read the content of the file

--

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Davy zhang

at Mar 7, 2013 at 9:18 am

⇧

I get it, there's a race condition here, I didn't realize it at the first
place. Your point 2 is the main reason of my problem. Thanks so much for
helping me out
The test may seemed weird, I know. But the real case I am working on is to
save mem content to disk at certain time, so I need to update the file
(truncating it) every-time I open it and write to it.
for your point3 , I just write a test code to test if the content been
successfully written, maybe time.Sleep() more suitable ?

On Thursday, March 7, 2013 3:24:05 PM UTC+8, Tamás Gulácsi wrote:

Works consistently.
Just for the record, my /tmp is a tmpfs...

Questions:
1. why do you open the file with truncating in each goroutine, and not
close the file handler at the end?
2. why don't you synchronize betweem the trunncates and the read? If you
read just when the goroutine opens (ant truncates) the file, than you will
read zero length.
3. what do you test here? Two instances of time.Tick don't happen at once.

GThomas

2013/3/7 davy zhang <davy...@gmail.com <javascript:>>

Thanks for the test, but could you run few more times? This test
sometimes is right, but not always. Thanks again.

On Thu, Mar 7, 2013 at 2:14 PM, Tamás Gulácsi <tgula...@gmail.com<javascript:>

wrote:
It works for me
gthomas@waterhouse /tmp % go test -v x_test.go
warning: building out-of-date packages:
flag
text/tabwriter
runtime/pprof
testing
installing these packages with 'go test -i x_test.go' will speed future
tests.

=== RUN TestStoreFileSave
updated value 12345789 /tmp/filesave
written 8
updated value 12345789 /tmp/filesave
written 8
12345789
--- PASS: TestStoreFileSave (2.00 seconds)
PASS
ok command-line-arguments 2.018s

gthomas@waterhouse /tmp % go version
go version devel +08dc15884e88 Mon Feb 25 08:29:46 2013 -0800 linux/amd64

GThomas

2013. március 7., csütörtök 6:57:36 UTC+1 időpontban davy zhang a
következőt írta:

I used sync and os.O_SYNC

http://play.golang.org/p/**q5SA0eV2pi<http://play.golang.org/p/q5SA0eV2pi>

but the result is the same

but when manually open the file using less /tmp/filesave

the content is there! So the file is written actually but the problem
is the way I read it?

On Thursday, March 7, 2013 1:45:00 PM UTC+8, davy zhang wrote:

but when I put

time.Sleep(1 * time.Second)

after the

<-time.Tick(2 * time.Second)

the file can be read after that, so is there explanation ?

On Thursday, March 7, 2013 1:42:21 PM UTC+8, davy zhang wrote:

code first
http://play.golang.org/p/**YldOJZNg1a<http://play.golang.org/p/YldOJZNg1a>

its been report written 2 times, but after 2 seconds tick the main
function can not read the content of the file

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Tamás Gulácsi

at Mar 7, 2013 at 9:28 am

⇧

No, Tick is ok, but you have to signal the reader that the writing isdone. Can be a mutex, or a channel.

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Davy zhang

at Mar 7, 2013 at 9:32 am

⇧

You'r totally right, I gonna add a mutex there. Thanks again

On Thursday, March 7, 2013 5:28:11 PM UTC+8, Tamás Gulácsi wrote:

No, Tick is ok, but you have to signal the reader that the writing isdone.
Can be a mutex, or a channel.

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Jan Mercl

at Mar 7, 2013 at 7:27 am

⇧

On Thu, Mar 7, 2013 at 6:42 AM, davy zhang wrote:
code first
http://play.golang.org/p/YldOJZNg1a

its been report written 2 times, but after 2 seconds tick the main function
can not read the content of the file

Your OS has a write cache and your program has a (file content) race
condition. Use http://golang.org/pkg/os/#File.Sync.

-j

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[go-nuts] Why file write in routine can not be read outside?

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