Ggthjy

1970s scifi/horror novel where protagonist is used by a crablike creature to feed its larvae, goes mad, and is defeated by retraumatising him

Practical reasons to have both a large police force and bounty hunting network?

Is there a frame of reference in which I was born before I was conceived?

A peculiar integral identity

Is there a way to find out the age of climbing ropes?

PTIJ: Aharon, King of Egypt

Specific Chinese carabiner QA?

Can we carry rice to Japan?

Would the melodic leap of the opening phrase of Mozart's K545 be considered dissonant?

Can an earth elemental drown/bury its opponent underground using earth glide?

Did Amazon pay $0 in taxes last year?

PTIJ: Why can't I sing about soda on certain days?

Misplaced tyre lever - alternatives?

Redirecting CellPrint output

What is a term for a function that when called repeatedly, has the same effect as calling once?

Lock enemy's y-axis when using Vector3.MoveTowards to follow the player

The need of reserving one's ability in job interviews

How to merge row in the first column in LaTeX

“I had a flat in the centre of town, but I didn’t like living there, so …”

How to disable or uninstall iTunes under High Sierra without disabling SIP

Why doesn't "adolescent" take any articles in "listen to adolescent agonising"?

Correct physics behind the colors on CD (compact disc)?

Can I solder 12/2 Romex to extend wire 5 ft?

If nine coins are tossed, what is the probability that the number of heads is even?

is 'sed' thread safe

What should someone know about using Python scripts in the shell?Nexenta bash script uses /usr/sun/bin/sed instead of /usr/bin/sedLeft and right square brackets treated differently by sed/bashsystemd daemon & python getting the wrong timesed multiple statements within a single command not workingHow to use sed to substitute strings which has “” in it?Python process can't create a file in a directory, keeps getting `permission denied` IOErrorIs a light weight process attached to a kernel thread in Linux?Extract every 2 lines from a 40 lines file and create a new fileRHEL upload / pull scripts from people without access to the server itseld

2

If I have a shell/python script that uses sed to modify a file in place based on user inputs, and then two users run the same script at the same time or approx. same time, is 'sed' thread safe ? Or perhaps it is not an issue because the file_descripor that was opened by the first thread will be used to lock the file anyway ? thx

linux sed python

share|improve this question

edited 4 hours ago

Jeff Schaller

42.9k1159137

asked 4 hours ago

terreysterreys

1613

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Slightly more info wanted. How do you use sed from Python (and why, can't Python do things like that fairly effortlessly?).
  
  – Kusalananda
  4 hours ago
  

  
  
  
  

add a comment | 

2

If I have a shell/python script that uses sed to modify a file in place based on user inputs, and then two users run the same script at the same time or approx. same time, is 'sed' thread safe ? Or perhaps it is not an issue because the file_descripor that was opened by the first thread will be used to lock the file anyway ? thx

linux sed python

share|improve this question

edited 4 hours ago

Jeff Schaller

42.9k1159137

asked 4 hours ago

terreysterreys

1613

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Slightly more info wanted. How do you use sed from Python (and why, can't Python do things like that fairly effortlessly?).
  
  – Kusalananda
  4 hours ago
  

  
  
  
  

add a comment | 

If I have a shell/python script that uses sed to modify a file in place based on user inputs, and then two users run the same script at the same time or approx. same time, is 'sed' thread safe ? Or perhaps it is not an issue because the file_descripor that was opened by the first thread will be used to lock the file anyway ? thx

linux sed python

share|improve this question

edited 4 hours ago

Jeff Schaller

42.9k1159137

asked 4 hours ago

terreysterreys

1613

share|improve this question

edited 4 hours ago

Jeff Schaller

42.9k1159137

asked 4 hours ago

terreysterreys

1613

share|improve this question

edited 4 hours ago

Jeff Schaller

42.9k1159137

asked 4 hours ago

terreysterreys

1613

edited 4 hours ago

Jeff Schaller

42.9k1159137

edited 4 hours ago

Jeff Schaller

42.9k1159137

asked 4 hours ago

terreysterreys

1613

asked 4 hours ago

terreysterreys

1613

1 Answer
1

active

oldest

votes

4

I'm not going to nitpick on the awful terminology, but yes, GNU sed with its -i ("in-place") flag could be safely used by more than one process at the same time without any extra locking, because sed is not actually modifying the file in-place, but it's redirecting the output to a temporary file, and if everything goes well, it will rename(2) (move) the temporary file to the original file, and the rename(2) is guaranteed to be atomic:

$ strace sed -i s/o/e/g foo.txt

open("foo.txt", O_RDONLY)               = 3

...

open("./sedDe80VL", O_RDWR|O_CREAT|O_EXCL, 0600) = 4

...

read(3, "foon", 4096)                  = 4

...

write(4, "feen", 4)                    = 4

read(3, "", 4096)                       = 0

...

close(3)                                = 0

close(4)                                = 0

rename("./sedDe80VL", "foo.txt")        = 0

At any point, foo.txt will refer either to the complete original file or to the complete processed file, never to something in between the two.

share|improve this answer

edited 4 hours ago

answered 4 hours ago

mosvymosvy

7,7821530

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  But what can happen is that two copies of sed start reading the file, make different changes, storing them to their respective temporary files, which are then renamed into place one after other, without regard for the fact that there was another sed working on the file at the same time. The changes made by one of the sed processes would be lost.
  
  – ilkkachu
  4 hours ago
  
  
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  @ilkkachu that will still be completely consistent -- the file will be either modified by both processes in turn (in any order) or by just one of them. At no point will the file contain garbage resulting from both processes modifying it at the same time.
  
  – mosvy
  4 hours ago
  

  
  
  
  


• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  it won't be total garbage, but having changes lost can still be an issue. The question refers to the file "being locked", and locking would usually refer to the second sed process waiting until the first completed. That might just be awful terminology on their part; it's hard to say what they really care about, but that particular issue is still possible.
  
  – ilkkachu
  3 hours ago
  

  
  
  
  

add a comment | 

Your Answer

StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "106"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);

StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});

function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: false,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: null,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});


}
});

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});

Sign up using Google

Sign up using Facebook

Sign up using Email and Password

Post as a guest

Name

Email

Required, but never shown

StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2funix.stackexchange.com%2fquestions%2f504810%2fis-sed-thread-safe%23new-answer', 'question_page');
}
);

Post as a guest

Name

Email

Required, but never shown

4

I'm not going to nitpick on the awful terminology, but yes, GNU sed with its -i ("in-place") flag could be safely used by more than one process at the same time without any extra locking, because sed is not actually modifying the file in-place, but it's redirecting the output to a temporary file, and if everything goes well, it will rename(2) (move) the temporary file to the original file, and the rename(2) is guaranteed to be atomic:

$ strace sed -i s/o/e/g foo.txt

open("foo.txt", O_RDONLY)               = 3

...

open("./sedDe80VL", O_RDWR|O_CREAT|O_EXCL, 0600) = 4

...

read(3, "foon", 4096)                  = 4

...

write(4, "feen", 4)                    = 4

read(3, "", 4096)                       = 0

...

close(3)                                = 0

close(4)                                = 0

rename("./sedDe80VL", "foo.txt")        = 0

At any point, foo.txt will refer either to the complete original file or to the complete processed file, never to something in between the two.

share|improve this answer

edited 4 hours ago

answered 4 hours ago

mosvymosvy

7,7821530

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  But what can happen is that two copies of sed start reading the file, make different changes, storing them to their respective temporary files, which are then renamed into place one after other, without regard for the fact that there was another sed working on the file at the same time. The changes made by one of the sed processes would be lost.
  
  – ilkkachu
  4 hours ago
  
  
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  @ilkkachu that will still be completely consistent -- the file will be either modified by both processes in turn (in any order) or by just one of them. At no point will the file contain garbage resulting from both processes modifying it at the same time.
  
  – mosvy
  4 hours ago
  

  
  
  
  


• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  it won't be total garbage, but having changes lost can still be an issue. The question refers to the file "being locked", and locking would usually refer to the second sed process waiting until the first completed. That might just be awful terminology on their part; it's hard to say what they really care about, but that particular issue is still possible.
  
  – ilkkachu
  3 hours ago
  

  
  
  
  

add a comment | 

4

I'm not going to nitpick on the awful terminology, but yes, GNU sed with its -i ("in-place") flag could be safely used by more than one process at the same time without any extra locking, because sed is not actually modifying the file in-place, but it's redirecting the output to a temporary file, and if everything goes well, it will rename(2) (move) the temporary file to the original file, and the rename(2) is guaranteed to be atomic:

$ strace sed -i s/o/e/g foo.txt

open("foo.txt", O_RDONLY)               = 3

...

open("./sedDe80VL", O_RDWR|O_CREAT|O_EXCL, 0600) = 4

...

read(3, "foon", 4096)                  = 4

...

write(4, "feen", 4)                    = 4

read(3, "", 4096)                       = 0

...

close(3)                                = 0

close(4)                                = 0

rename("./sedDe80VL", "foo.txt")        = 0

At any point, foo.txt will refer either to the complete original file or to the complete processed file, never to something in between the two.

share|improve this answer

edited 4 hours ago

answered 4 hours ago

mosvymosvy

7,7821530

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  But what can happen is that two copies of sed start reading the file, make different changes, storing them to their respective temporary files, which are then renamed into place one after other, without regard for the fact that there was another sed working on the file at the same time. The changes made by one of the sed processes would be lost.
  
  – ilkkachu
  4 hours ago
  
  
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  @ilkkachu that will still be completely consistent -- the file will be either modified by both processes in turn (in any order) or by just one of them. At no point will the file contain garbage resulting from both processes modifying it at the same time.
  
  – mosvy
  4 hours ago
  

  
  
  
  


• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  it won't be total garbage, but having changes lost can still be an issue. The question refers to the file "being locked", and locking would usually refer to the second sed process waiting until the first completed. That might just be awful terminology on their part; it's hard to say what they really care about, but that particular issue is still possible.
  
  – ilkkachu
  3 hours ago
  

  
  
  
  

add a comment | 

I'm not going to nitpick on the awful terminology, but yes, GNU sed with its -i ("in-place") flag could be safely used by more than one process at the same time without any extra locking, because sed is not actually modifying the file in-place, but it's redirecting the output to a temporary file, and if everything goes well, it will rename(2) (move) the temporary file to the original file, and the rename(2) is guaranteed to be atomic:

$ strace sed -i s/o/e/g foo.txt

open("foo.txt", O_RDONLY)               = 3

...

open("./sedDe80VL", O_RDWR|O_CREAT|O_EXCL, 0600) = 4

...

read(3, "foon", 4096)                  = 4

...

write(4, "feen", 4)                    = 4

read(3, "", 4096)                       = 0

...

close(3)                                = 0

close(4)                                = 0

rename("./sedDe80VL", "foo.txt")        = 0

At any point, foo.txt will refer either to the complete original file or to the complete processed file, never to something in between the two.

share|improve this answer

edited 4 hours ago

answered 4 hours ago

mosvymosvy

7,7821530

$ strace sed -i s/o/e/g foo.txt

open("foo.txt", O_RDONLY)               = 3

...

open("./sedDe80VL", O_RDWR|O_CREAT|O_EXCL, 0600) = 4

...

read(3, "foon", 4096)                  = 4

...

write(4, "feen", 4)                    = 4

read(3, "", 4096)                       = 0

...

close(3)                                = 0

close(4)                                = 0

rename("./sedDe80VL", "foo.txt")        = 0

share|improve this answer

edited 4 hours ago

answered 4 hours ago

mosvymosvy

7,7821530

answered 4 hours ago

mosvymosvy

7,7821530

answered 4 hours ago

mosvymosvy

7,7821530