Check if a file is not open nor being used by another process
Question:
I my application, i have below requests:
1. There has one thread will regularly record some logs in file. The log file will be rollovered in certain interval. for keeping the log files small.
2. There has another thread also will regularly to process these log files. ex: Move the log files to other place, parse the log’s content to generate some log reports.
But, there has a condition is the second thread can not process the log file that’s using to record the log. in code side, the pseudocode similars like below:
#code in second thread to process the log files
for logFile in os.listdir(logFolder):
if not file_is_open(logFile) or file_is_use(logFile):
ProcessLogFile(logFile) # move log file to other place, and generate log report....
So, how do i check is a file is already open or is used by other process?
I did some research in internet. And have some results:
try:
myfile = open(filename, "r+") # or "a+", whatever you need
except IOError:
print "Could not open file! Please close Excel!"
I tried this code, but it doesn’t work, no matter i use “r+” or “a+” flag
try:
os.remove(filename) # try to remove it directly
except OSError as e:
if e.errno == errno.ENOENT: # file doesn't exist
break
This code can work, but it can not reach my request, since i don’t want to delete the file to check if it is open.
Answers:
An issue with trying to find out if a file is being used by another process is the possibility of a race condition. You could check a file, decide that it is not in use, then just before you open it another process (or thread) leaps in and grabs it (or even deletes it).
Ok, let’s say you decide to live with that possibility and hope it does not occur. To check files in use by other processes is operating system dependant.
On Linux it is fairly easy, just iterate through the PIDs in /proc. Here is a generator that iterates over files in use for a specific PID:
def iterate_fds(pid):
dir = '/proc/'+str(pid)+'/fd'
if not os.access(dir,os.R_OK|os.X_OK): return
for fds in os.listdir(dir):
for fd in fds:
full_name = os.path.join(dir, fd)
try:
file = os.readlink(full_name)
if file == '/dev/null' or
re.match(r'pipe:[d+]',file) or
re.match(r'socket:[d+]',file):
file = None
except OSError as err:
if err.errno == 2:
file = None
else:
raise(err)
yield (fd,file)
On Windows it is not quite so straightforward, the APIs are not published. There is a sysinternals tool (handle.exe) that can be used, but I recommend the PyPi module psutil, which is portable (i.e., it runs on Linux as well, and probably on other OS):
import psutil
for proc in psutil.process_iter():
try:
# this returns the list of opened files by the current process
flist = proc.open_files()
if flist:
print(proc.pid,proc.name)
for nt in flist:
print("t",nt.path)
# This catches a race condition where a process ends
# before we can examine its files
except psutil.NoSuchProcess as err:
print("****",err)
You can use inotify to watch for activity in file system. You can watch for file close events, indicating that a roll-over has happened. You should also add additional condition on file-size. Make sure you filter out file close events from the second thread.
Instead on using os.remove() you may use the following workaround on Windows:
import os
file = "D:\temp\test.pdf"
if os.path.exists(file):
try:
os.rename(file,file+"_")
print "Access on file "" + str(file) +"" is available!"
os.rename(file+"_",file)
except OSError as e:
message = "Access-error on file "" + str(file) + ""!!! n" + str(e)
print message
I like Daniel’s answer, but for Windows users, I realized that it’s safer and simpler to rename the file to the name it already has. That solves the problems brought up in the comments to his answer. Here’s the code:
import os
f = 'C:/test.xlsx'
if os.path.exists(f):
try:
os.rename(f, f)
print 'Access on file "' + f +'" is available!'
except OSError as e:
print 'Access-error on file "' + f + '"! n' + str(e)
You can check if a file has a handle on it using the next function (remember to pass the full path to that file):
import psutil
def has_handle(fpath):
for proc in psutil.process_iter():
try:
for item in proc.open_files():
if fpath == item.path:
return True
except Exception:
pass
return False
I know I’m late to the party but I also had this problem and I used the lsof command to solve it (which I think is new from the approaches mentioned above). With lsof we can basically check for the processes that are using this particular file.
Here is how I did it:
from subprocess import check_output,Popen, PIPE
try:
lsout=Popen(['lsof',filename],stdout=PIPE, shell=False)
check_output(["grep",filename], stdin=lsout.stdout, shell=False)
except:
#check_output will throw an exception here if it won't find any process using that file
just write your log processing code in the except part and you are good to go.
A slightly more polished version of one of the answers from above.
from pathlib import Path
def is_file_in_use(file_path):
path = Path(file_path)
if not path.exists():
raise FileNotFoundError
try:
path.rename(path)
except PermissionError:
return True
else:
return False
I provided one solution. please see the following code.
def isFileinUsed(ifile):
widlcard = "/proc/*/fd/*"
lfds = glob.glob(widlcard)
for fds in lfds:
try:
file = os.readlink(fds)
if file == ifile:
return True
except OSError as err:
if err.errno == 2:
file = None
else:
raise(err)
return False
You can use this function to check if a file is in used.
Note:
This solution only can be used for Linux system.
I my application, i have below requests:
1. There has one thread will regularly record some logs in file. The log file will be rollovered in certain interval. for keeping the log files small.
2. There has another thread also will regularly to process these log files. ex: Move the log files to other place, parse the log’s content to generate some log reports.
But, there has a condition is the second thread can not process the log file that’s using to record the log. in code side, the pseudocode similars like below:
#code in second thread to process the log files
for logFile in os.listdir(logFolder):
if not file_is_open(logFile) or file_is_use(logFile):
ProcessLogFile(logFile) # move log file to other place, and generate log report....
So, how do i check is a file is already open or is used by other process?
I did some research in internet. And have some results:
try:
myfile = open(filename, "r+") # or "a+", whatever you need
except IOError:
print "Could not open file! Please close Excel!"
I tried this code, but it doesn’t work, no matter i use “r+” or “a+” flag
try:
os.remove(filename) # try to remove it directly
except OSError as e:
if e.errno == errno.ENOENT: # file doesn't exist
break
This code can work, but it can not reach my request, since i don’t want to delete the file to check if it is open.
An issue with trying to find out if a file is being used by another process is the possibility of a race condition. You could check a file, decide that it is not in use, then just before you open it another process (or thread) leaps in and grabs it (or even deletes it).
Ok, let’s say you decide to live with that possibility and hope it does not occur. To check files in use by other processes is operating system dependant.
On Linux it is fairly easy, just iterate through the PIDs in /proc. Here is a generator that iterates over files in use for a specific PID:
def iterate_fds(pid):
dir = '/proc/'+str(pid)+'/fd'
if not os.access(dir,os.R_OK|os.X_OK): return
for fds in os.listdir(dir):
for fd in fds:
full_name = os.path.join(dir, fd)
try:
file = os.readlink(full_name)
if file == '/dev/null' or
re.match(r'pipe:[d+]',file) or
re.match(r'socket:[d+]',file):
file = None
except OSError as err:
if err.errno == 2:
file = None
else:
raise(err)
yield (fd,file)
On Windows it is not quite so straightforward, the APIs are not published. There is a sysinternals tool (handle.exe) that can be used, but I recommend the PyPi module psutil, which is portable (i.e., it runs on Linux as well, and probably on other OS):
import psutil
for proc in psutil.process_iter():
try:
# this returns the list of opened files by the current process
flist = proc.open_files()
if flist:
print(proc.pid,proc.name)
for nt in flist:
print("t",nt.path)
# This catches a race condition where a process ends
# before we can examine its files
except psutil.NoSuchProcess as err:
print("****",err)
You can use inotify to watch for activity in file system. You can watch for file close events, indicating that a roll-over has happened. You should also add additional condition on file-size. Make sure you filter out file close events from the second thread.
Instead on using os.remove() you may use the following workaround on Windows:
import os
file = "D:\temp\test.pdf"
if os.path.exists(file):
try:
os.rename(file,file+"_")
print "Access on file "" + str(file) +"" is available!"
os.rename(file+"_",file)
except OSError as e:
message = "Access-error on file "" + str(file) + ""!!! n" + str(e)
print message
I like Daniel’s answer, but for Windows users, I realized that it’s safer and simpler to rename the file to the name it already has. That solves the problems brought up in the comments to his answer. Here’s the code:
import os
f = 'C:/test.xlsx'
if os.path.exists(f):
try:
os.rename(f, f)
print 'Access on file "' + f +'" is available!'
except OSError as e:
print 'Access-error on file "' + f + '"! n' + str(e)
You can check if a file has a handle on it using the next function (remember to pass the full path to that file):
import psutil
def has_handle(fpath):
for proc in psutil.process_iter():
try:
for item in proc.open_files():
if fpath == item.path:
return True
except Exception:
pass
return False
I know I’m late to the party but I also had this problem and I used the lsof command to solve it (which I think is new from the approaches mentioned above). With lsof we can basically check for the processes that are using this particular file.
Here is how I did it:
from subprocess import check_output,Popen, PIPE
try:
lsout=Popen(['lsof',filename],stdout=PIPE, shell=False)
check_output(["grep",filename], stdin=lsout.stdout, shell=False)
except:
#check_output will throw an exception here if it won't find any process using that file
just write your log processing code in the except part and you are good to go.
A slightly more polished version of one of the answers from above.
from pathlib import Path
def is_file_in_use(file_path):
path = Path(file_path)
if not path.exists():
raise FileNotFoundError
try:
path.rename(path)
except PermissionError:
return True
else:
return False
I provided one solution. please see the following code.
def isFileinUsed(ifile):
widlcard = "/proc/*/fd/*"
lfds = glob.glob(widlcard)
for fds in lfds:
try:
file = os.readlink(fds)
if file == ifile:
return True
except OSError as err:
if err.errno == 2:
file = None
else:
raise(err)
return False
You can use this function to check if a file is in used.
Note:
This solution only can be used for Linux system.