I can't get the following code for Detecting USB Device Insertion to work on my Windows 10 (64 bit) computer with Python 3.7.
import win32serviceutil
import win32service
import win32event
import servicemanager
import win32gui
import win32gui_struct
struct = win32gui_struct.struct
pywintypes = win32gui_struct.pywintypes
import win32con
GUID_DEVINTERFACE_USB_DEVICE = "{A5DCBF10-6530-11D2-901F-00C04FB951ED}"
DBT_DEVICEARRIVAL = 0x8000
DBT_DEVICEREMOVECOMPLETE = 0x8004
import ctypes
#
# Cut-down clone of UnpackDEV_BROADCAST from win32gui_struct, to be
# used for monkey-patching said module with correct handling
# of the "name" param of DBT_DEVTYPE_DEVICEINTERFACE
#
def _UnpackDEV_BROADCAST (lparam):
if lparam == 0: return None
hdr_format = "iii"
hdr_size = struct.calcsize (hdr_format)
hdr_buf = win32gui.PyGetMemory (lparam, hdr_size)
size, devtype, reserved = struct.unpack ("iii", hdr_buf)
# Due to x64 alignment issues, we need to use the full format string over
# the entire buffer. ie, on x64:
# calcsize('iiiP') != calcsize('iii')+calcsize('P')
buf = win32gui.PyGetMemory (lparam, size)
extra = {}
if devtype == win32con.DBT_DEVTYP_DEVICEINTERFACE:
fmt = hdr_format + "16s"
_, _, _, guid_bytes = struct.unpack (fmt, buf[:struct.calcsize(fmt)])
extra['classguid'] = pywintypes.IID (guid_bytes, True)
extra['name'] = ctypes.wstring_at (lparam + struct.calcsize(fmt))
else:
raise NotImplementedError("unknown device type %d" % (devtype,))
return win32gui_struct.DEV_BROADCAST_INFO(devtype, **extra)
win32gui_struct.UnpackDEV_BROADCAST = _UnpackDEV_BROADCAST
class DeviceEventService (win32serviceutil.ServiceFramework):
_svc_name_ = "DevEventHandler"
_svc_display_name_ = "Device Event Handler"
_svc_description_ = "Handle device notification events"
def __init__(self, args):
win32serviceutil.ServiceFramework.__init__ (self, args)
self.hWaitStop = win32event.CreateEvent (None, 0, 0, None)
#
# Specify that we're interested in device interface
# events for USB devices
#
filter = win32gui_struct.PackDEV_BROADCAST_DEVICEINTERFACE (
GUID_DEVINTERFACE_USB_DEVICE
)
self.hDevNotify = win32gui.RegisterDeviceNotification (
self.ssh, # copy of the service status handle
filter,
win32con.DEVICE_NOTIFY_SERVICE_HANDLE
)
#
# Add to the list of controls already handled by the underlying
# ServiceFramework class. We're only interested in device events
#
def GetAcceptedControls(self):
rc = win32serviceutil.ServiceFramework.GetAcceptedControls (self)
rc |= win32service.SERVICE_CONTROL_DEVICEEVENT
return rc
#
# Handle non-standard service events (including our device broadcasts)
# by logging to the Application event log
#
def SvcOtherEx(self, control, event_type, data):
if control == win32service.SERVICE_CONTROL_DEVICEEVENT:
info = win32gui_struct.UnpackDEV_BROADCAST(data)
#
# This is the key bit here where you'll presumably
# do something other than log the event. Perhaps pulse
# a named event or write to a secure pipe etc. etc.
#
if event_type == DBT_DEVICEARRIVAL:
servicemanager.LogMsg (
servicemanager.EVENTLOG_INFORMATION_TYPE,
0xF000,
("Device %s arrived" % info.name, '')
)
elif event_type == DBT_DEVICEREMOVECOMPLETE:
servicemanager.LogMsg (
servicemanager.EVENTLOG_INFORMATION_TYPE,
0xF000,
("Device %s removed" % info.name, '')
)
#
# Standard stuff for stopping and running service; nothing
# specific to device notifications
#
def SvcStop(self):
self.ReportServiceStatus (win32service.SERVICE_STOP_PENDING)
win32event.SetEvent (self.hWaitStop)
def SvcDoRun(self):
win32event.WaitForSingleObject (self.hWaitStop, win32event.INFINITE)
servicemanager.LogMsg (
servicemanager.EVENTLOG_INFORMATION_TYPE,
servicemanager.PYS_SERVICE_STOPPED,
(self._svc_name_, '')
)
if __name__=='__main__':
win32serviceutil.HandleCommandLine (DeviceEventService)
I start the script with the following command: python main.py start
Then the following error messages appear in the command prompt:
Starting service DevEventHandler
Error starting service: Access denied
I then ran the script with administrator privileges: runas /user:administrator "python main.py start"
Another error messages appear in the command prompt:
Starting service DevEventHandler
Error starting service: The specified service does not exist as an installed service.
How can the 'The specified service does not exist as an installed service' error be fixed?
I tested with Python 3.8.2 x64.
Install pywin32 (pip install pywin32)
Install the current/last version (1.5) of the WMI module from https://github.com/tjguk/wmi (pip install -e git+https://github.com/tjguk/wmi.git#egg=wmi)
run a script (test.py in my case), like:
import wmi
raw_wql = "SELECT * FROM __InstanceCreationEvent WITHIN 2 WHERE TargetInstance ISA \'Win32_USBHub\'"
c = wmi.WMI ()
watcher = c.watch_for(raw_wql=raw_wql)
while 1:
usb = watcher ()
print(usb)
plug in a USB device. Output looks like:
(wmi-py) C:\Users\USER\Source\wmi-py>py test.py
instance of Win32_USBHub
{
Caption = "USB Composite Device";
ConfigManagerErrorCode = 0;
ConfigManagerUserConfig = FALSE;
CreationClassName = "Win32_USBHub";
Description = "USB Composite Device";
...
Many thanks to the WMI module author, and the Windows nerds' discussion here Detecting USB drive insertion and removal using windows service and c#
I tried to run the script with debug argument and a message saying that service is not installed appeared.
Try first to type
python main.py install
then
python main.py start
I have created a windwos service utilising the following code:
import win32service
import win32serviceutil
import win32api
import win32con
import win32event
import win32evtlogutil
import os, sys, string, time
class aservice(win32serviceutil.ServiceFramework):
_svc_name_ = "PAStoDistillerIFC"
_svc_display_name_ = "PAS DW to Distiller Interface"
_svc_description_ = "Service that checks the Clinical Research folder for any new files from PAS to process in Distiller"
def __init__(self, args):
win32serviceutil.ServiceFramework.__init__(self, args)
self.hWaitStop = win32event.CreateEvent(None, 0, 0, None)
def SvcStop(self):
self.ReportServiceStatus(win32service.SERVICE_STOP_PENDING)
win32event.SetEvent(self.hWaitStop)
def SvcDoRun(self):
import servicemanager
servicemanager.LogMsg(servicemanager.EVENTLOG_INFORMATION_TYPE,servicemanager.PYS_SERVICE_STARTED,(self._svc_name_, ''))
#self.timeout = 640000 #640 seconds / 10 minutes (value is in milliseconds)
self.timeout = 120000 #120 seconds / 2 minutes
# This is how long the service will wait to run / refresh itself (see script below)
while 1:
# Wait for service stop signal, if timeout, loop again
rc = win32event.WaitForSingleObject(self.hWaitStop, self.timeout)
# Check to see if self.hWaitStop happened
if rc == win32event.WAIT_OBJECT_0:
# Stop signal encountered
servicemanager.LogInfoMsg("PAStoDistillerIFC - STOPPED!") #For Event Log
break
else:
#[actual service code between rests]
try:
file_path = "D:\\SCRIPTS\\script.py"
execfile(file_path) #Execute the script
except:
servicemanager.LogInfoMsg("File CRASHED")
pass
#[actual service code between rests]
def ctrlHandler(ctrlType):
return True
if __name__ == '__main__':
win32api.SetConsoleCtrlHandler(ctrlHandler, True)
win32serviceutil.HandleCommandLine(aservice)
To run this script:
import os, re, urllib, urllib2, time, datetime
def postXML( path, fname):
fileresultop = open("D:\\CLinicalResearch\\SCRIPTS\\LOG.txt", 'a') # open result file
fileresultop.write('CheckXXX ')
fileresultop.close()
now = datetime.datetime.now() #####ALWAYS CRASHES HERE######
fileresult = open("D:\\SCRIPTS\\IFCPYTHONLOG.txt", 'a') # open result file
fileresultop = open("D:\\SCRIPTS\\LOG.txt", 'a')
fileresultop.write('Check2 ')
fileresultop.close()
path="D:\\Test2" # Put location of XML files here.
procpath="D:\\Test2Processed" # Location of processed files
now = datetime.datetime.now()
dirList=os.listdir(path)
for fname in dirList: # For each file in directory
if re.search("PatientIndexInsert", fname): # Brand new patient records
fileresultop = open("D:\\SCRIPTS\\LOG.txt", 'a') # open result file
fileresultop.write('Check1 ')
fileresultop.close()
postXML(path, fname)
I have pared down the script to the bare code where I believe this is crashing.
This works perfectly from the command line, I run the windows service under my own login.
Once I take the datetime function out of the function it seems to work.
Edit 1: I saw that the service runs in a blank environment. I don't have any environmental variables set myself.
Edit 2: Added traceback:
File "D:\ClinicalResearch\SCRIPTS\PAS2DIST.py", line 23, in <module>
postXML(path, fname)
File "D:\ClinicalResearch\SCRIPTS\PAS2DIST.py", line 6, in postXML
now = datetime.datetime.now()
NameError: global name 'datetime' is not defined
I didn't find the cause but I did find a workaround.
I needed to import all the same libraries into the function too. Once I did that, worked like a charm.
Hope this can help someone else.
I am fairly new to python, and have no experience with writing services for windows. I have tried to hack together a windows service based on afew tutorials i have found out there.
I need this service to constantly monitor a directory for changes and when it sees a change it runs a script. Here is what i have so far:
import win32service
import win32serviceutil
import time
class aservice(win32serviceutil.ServiceFramework):
_svc_name_ = "aservice"
_svc_display_name_ = "aservice - It Does nothing"
def __init__(self,args):
win32serviceutil.ServiceFramework.__init__(self,args)
self.isAlive = True
def SvcDoRun(self):
import servicemanager
while self.isAlive:
# This is where i am trying to run my code...is that right?
self.main()
#servicemanager.LogInfoMsg("aservice - is alive and well")
#time.sleep(5)
#servicemanager.LogInfoMsg("aservice - Stopped")
def SvcStop(self):
import servicemanager
servicemanager.LogInfoMsg("aservice - Recieved stop signal")
self.ReportServiceStatus(win32service.SERVICE_STOP_PENDING)
self.isAlive = False #this will make SvcDoRun() break the while loop at the next iteration.
# This code monitors a directory for changes and calls a script when there is a change
# At the moment, it creates a log file instead of calling the script
def main(self):
import os
import win32file
import win32con
ACTIONS = {
1: "Created",
2: "Deleted",
3: "Updated",
4: "Renamed from something",
5: "Ranamed to something"
}
FILE_LIST_DIRECTORY = 0x0001
path_to_watch = "folder"
hDir = win32file.CreateFile (
path_to_watch,
FILE_LIST_DIRECTORY,
win32con.FILE_SHARE_READ | win32con.FILE_SHARE_WRITE,
None,
win32con.OPEN_EXISTING,
win32con.FILE_FLAG_BACKUP_SEMANTICS,
None
)
while 1:
results = win32file.ReadDirectoryChangesW (
hDir,
1024,
True,
win32con.FILE_NOTIFY_CHANGE_FILE_NAME |
win32con.FILE_NOTIFY_CHANGE_DIR_NAME |
win32con.FILE_NOTIFY_CHANGE_ATTRIBUTES |
win32con.FILE_NOTIFY_CHANGE_SIZE |
win32con.FILE_NOTIFY_CHANGE_LAST_WRITE |
win32con.FILE_NOTIFY_CHANGE_SECURITY,
None,
None
)
for action, file in results:
#import script
log = open ('log.txt', 'w')
full_filename = os.path.join(path_to_watch)
log.write(full_filename + ACTIONS.get(action, "Unknown"))
log.close()
if __name__ == '__main__':
win32serviceutil.HandleCommandLine(aservice)
Any ideas on what i am doing wrong?
EDIT: Here is the event log error i am getting for it.
Event Type: Error
Event Source: aservice
Event Category: None
Event ID: 3
Date: 21/01/2010
Time: 11:27:43 AM
User: N/A
Computer:
Description:
The instance's SvcRun() method failed
Traceback (most recent call last):
File "C:\Python25\Lib\site-packages\win32\lib\win32serviceutil.py", line 806, in SvcRun
self.SvcDoRun()
File "D:\TEST\simpleservice2.py", line 35, in SvcDoRun
self.main()
File "D:\TEST\simpleservice2.py", line 72, in main
None
error: (2, 'CreateFile', 'The system cannot find the file specified.')
%2: %3
One thing to keep in mind with Windows services is that by default, they run under the LOCAL_SYSTEM account. This means that permissions to local volumes apply (LOCAL_SYSTEM can certainly be denied access to any given folder), and that LOCAL_SYSTEM does not have any access to any network volumes.
I'm not familiar with pywin32's ServiceFramework, but based on your code and the error message, I bet you have a problem with path_to_watch.
I assume you sanitized the folder name for your example, and you're not actually looking for folder.
How about:
Are you using the full path to the folder? The current working directory of the service may not be what you expect.
Are you escaping any backslashes in the folder path?
Try using:
path_to_watch = r"c:\foo\bar" + "\\"
Is there a Pythonic way to have only one instance of a program running?
The only reasonable solution I've come up with is trying to run it as a server on some port, then second program trying to bind to same port - fails. But it's not really a great idea, maybe there's something more lightweight than this?
(Take into consideration that program is expected to fail sometimes, i.e. segfault - so things like "lock file" won't work)
The following code should do the job, it is cross-platform and runs on Python 2.4-3.2. I tested it on Windows, OS X and Linux.
from tendo import singleton
me = singleton.SingleInstance() # will sys.exit(-1) if other instance is running
The latest code version is available singleton.py. Please file bugs here.
You can install tend using one of the following methods:
easy_install tendo
pip install tendo
manually by getting it from http://pypi.python.org/pypi/tendo
Simple, cross-platform solution, found in another question by zgoda:
import fcntl
import os
import sys
def instance_already_running(label="default"):
"""
Detect if an an instance with the label is already running, globally
at the operating system level.
Using `os.open` ensures that the file pointer won't be closed
by Python's garbage collector after the function's scope is exited.
The lock will be released when the program exits, or could be
released if the file pointer were closed.
"""
lock_file_pointer = os.open(f"/tmp/instance_{label}.lock", os.O_WRONLY)
try:
fcntl.lockf(lock_file_pointer, fcntl.LOCK_EX | fcntl.LOCK_NB)
already_running = False
except IOError:
already_running = True
return already_running
A lot like S.Lott's suggestion, but with the code.
This code is Linux specific. It uses 'abstract' UNIX domain sockets, but it is simple and won't leave stale lock files around. I prefer it to the solution above because it doesn't require a specially reserved TCP port.
try:
import socket
s = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
## Create an abstract socket, by prefixing it with null.
s.bind( '\0postconnect_gateway_notify_lock')
except socket.error as e:
error_code = e.args[0]
error_string = e.args[1]
print "Process already running (%d:%s ). Exiting" % ( error_code, error_string)
sys.exit (0)
The unique string postconnect_gateway_notify_lock can be changed to allow multiple programs that need a single instance enforced.
I don't know if it's pythonic enough, but in the Java world listening on a defined port is a pretty widely used solution, as it works on all major platforms and doesn't have any problems with crashing programs.
Another advantage of listening to a port is that you could send a command to the running instance. For example when the users starts the program a second time, you could send the running instance a command to tell it to open another window (that's what Firefox does, for example. I don't know if they use TCP ports or named pipes or something like that, 'though).
Never written python before, but this is what I've just implemented in mycheckpoint, to prevent it being started twice or more by crond:
import os
import sys
import fcntl
fh=0
def run_once():
global fh
fh=open(os.path.realpath(__file__),'r')
try:
fcntl.flock(fh,fcntl.LOCK_EX|fcntl.LOCK_NB)
except:
os._exit(0)
run_once()
Found Slava-N's suggestion after posting this in another issue (http://stackoverflow.com/questions/2959474). This one is called as a function, locks the executing scripts file (not a pid file) and maintains the lock until the script ends (normal or error).
Use a pid file. You have some known location, "/path/to/pidfile" and at startup you do something like this (partially pseudocode because I'm pre-coffee and don't want to work all that hard):
import os, os.path
pidfilePath = """/path/to/pidfile"""
if os.path.exists(pidfilePath):
pidfile = open(pidfilePath,"r")
pidString = pidfile.read()
if <pidString is equal to os.getpid()>:
# something is real weird
Sys.exit(BADCODE)
else:
<use ps or pidof to see if the process with pid pidString is still running>
if <process with pid == 'pidString' is still running>:
Sys.exit(ALREADAYRUNNING)
else:
# the previous server must have crashed
<log server had crashed>
<reopen pidfilePath for writing>
pidfile.write(os.getpid())
else:
<open pidfilePath for writing>
pidfile.write(os.getpid())
So, in other words, you're checking if a pidfile exists; if not, write your pid to that file. If the pidfile does exist, then check to see if the pid is the pid of a running process; if so, then you've got another live process running, so just shut down. If not, then the previous process crashed, so log it, and then write your own pid to the file in place of the old one. Then continue.
The best solution for this on windows is to use mutexes as suggested by #zgoda.
import win32event
import win32api
from winerror import ERROR_ALREADY_EXISTS
mutex = win32event.CreateMutex(None, False, 'name')
last_error = win32api.GetLastError()
if last_error == ERROR_ALREADY_EXISTS:
print("App instance already running")
Some answers use fctnl (included also in #sorin tendo package) which is not available on windows and should you try to freeze your python app using a package like pyinstaller which does static imports, it throws an error.
Also, using the lock file method, creates a read-only problem with database files( experienced this with sqlite3).
Here is my eventual Windows-only solution. Put the following into a module, perhaps called 'onlyone.py', or whatever. Include that module directly into your __ main __ python script file.
import win32event, win32api, winerror, time, sys, os
main_path = os.path.abspath(sys.modules['__main__'].__file__).replace("\\", "/")
first = True
while True:
mutex = win32event.CreateMutex(None, False, main_path + "_{<paste YOUR GUID HERE>}")
if win32api.GetLastError() == 0:
break
win32api.CloseHandle(mutex)
if first:
print "Another instance of %s running, please wait for completion" % main_path
first = False
time.sleep(1)
Explanation
The code attempts to create a mutex with name derived from the full path to the script. We use forward-slashes to avoid potential confusion with the real file system.
Advantages
No configuration or 'magic' identifiers needed, use it in as many different scripts as needed.
No stale files left around, the mutex dies with you.
Prints a helpful message when waiting
This may work.
Attempt create a PID file to a known location. If you fail, someone has the file locked, you're done.
When you finish normally, close and remove the PID file, so someone else can overwrite it.
You can wrap your program in a shell script that removes the PID file even if your program crashes.
You can, also, use the PID file to kill the program if it hangs.
For anybody using wxPython for their application, you can use the function wx.SingleInstanceChecker documented here.
I personally use a subclass of wx.App which makes use of wx.SingleInstanceChecker and returns False from OnInit() if there is an existing instance of the app already executing like so:
import wx
class SingleApp(wx.App):
"""
class that extends wx.App and only permits a single running instance.
"""
def OnInit(self):
"""
wx.App init function that returns False if the app is already running.
"""
self.name = "SingleApp-%s".format(wx.GetUserId())
self.instance = wx.SingleInstanceChecker(self.name)
if self.instance.IsAnotherRunning():
wx.MessageBox(
"An instance of the application is already running",
"Error",
wx.OK | wx.ICON_WARNING
)
return False
return True
This is a simple drop-in replacement for wx.App that prohibits multiple instances. To use it simply replace wx.App with SingleApp in your code like so:
app = SingleApp(redirect=False)
frame = wx.Frame(None, wx.ID_ANY, "Hello World")
frame.Show(True)
app.MainLoop()
Using a lock-file is a quite common approach on unix. If it crashes, you have to clean up manually. You could stor the PID in the file, and on startup check if there is a process with this PID, overriding the lock-file if not. (However, you also need a lock around the read-file-check-pid-rewrite-file). You will find what you need for getting and checking pid in the os-package. The common way of checking if there exists a process with a given pid, is to send it a non-fatal signal.
Other alternatives could be combining this with flock or posix semaphores.
Opening a network socket, as saua proposed, would probably be the easiest and most portable.
I'm posting this as an answer because I'm a new user and Stack Overflow won't let me vote yet.
Sorin Sbarnea's solution works for me under OS X, Linux and Windows, and I am grateful for it.
However, tempfile.gettempdir() behaves one way under OS X and Windows and another under other some/many/all(?) *nixes (ignoring the fact that OS X is also Unix!). The difference is important to this code.
OS X and Windows have user-specific temp directories, so a tempfile created by one user isn't visible to another user. By contrast, under many versions of *nix (I tested Ubuntu 9, RHEL 5, OpenSolaris 2008 and FreeBSD 8), the temp dir is /tmp for all users.
That means that when the lockfile is created on a multi-user machine, it's created in /tmp and only the user who creates the lockfile the first time will be able to run the application.
A possible solution is to embed the current username in the name of the lock file.
It's worth noting that the OP's solution of grabbing a port will also misbehave on a multi-user machine.
Building upon Roberto Rosario's answer, I come up with the following function:
SOCKET = None
def run_single_instance(uniq_name):
try:
import socket
global SOCKET
SOCKET = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
## Create an abstract socket, by prefixing it with null.
# this relies on a feature only in linux, when current process quits, the
# socket will be deleted.
SOCKET.bind('\0' + uniq_name)
return True
except socket.error as e:
return False
We need to define global SOCKET vaiable since it will only be garbage collected when the whole process quits. If we declare a local variable in the function, it will go out of scope after the function exits, thus the socket be deleted.
All the credit should go to Roberto Rosario, since I only clarify and elaborate upon his code. And this code will work only on Linux, as the following quoted text from https://troydhanson.github.io/network/Unix_domain_sockets.html explains:
Linux has a special feature: if the pathname for a UNIX domain socket
begins with a null byte \0, its name is not mapped into the
filesystem. Thus it won’t collide with other names in the filesystem.
Also, when a server closes its UNIX domain listening socket in the
abstract namespace, its file is deleted; with regular UNIX domain
sockets, the file persists after the server closes it.
Late answer, but for windows you can use:
from win32event import CreateMutex
from win32api import CloseHandle, GetLastError
from winerror import ERROR_ALREADY_EXISTS
import sys
class singleinstance:
""" Limits application to single instance """
def __init__(self):
self.mutexname = "testmutex_{D0E858DF-985E-4907-B7FB-8D732C3FC3B9}"
self.mutex = CreateMutex(None, False, self.mutexname)
self.lasterror = GetLastError()
def alreadyrunning(self):
return (self.lasterror == ERROR_ALREADY_EXISTS)
def __del__(self):
if self.mutex:
CloseHandle(self.mutex)
Usage
# do this at beginnig of your application
myapp = singleinstance()
# check is another instance of same program running
if myapp.alreadyrunning():
print ("Another instance of this program is already running")
sys.exit(1)
Here is a cross platform example that I've tested on Windows Server 2016 and Ubuntu 20.04 using Python 3.7.9:
import os
class SingleInstanceChecker:
def __init__(self, id):
if isWin():
ensure_win32api()
self.mutexname = id
self.lock = win32event.CreateMutex(None, False, self.mutexname)
self.running = (win32api.GetLastError() == winerror.ERROR_ALREADY_EXISTS)
else:
ensure_fcntl()
self.lock = open(f"/tmp/isnstance_{id}.lock", 'wb')
try:
fcntl.lockf(self.lock, fcntl.LOCK_EX | fcntl.LOCK_NB)
self.running = False
except IOError:
self.running = True
def already_running(self):
return self.running
def __del__(self):
if self.lock:
try:
if isWin():
win32api.CloseHandle(self.lock)
else:
os.close(self.lock)
except Exception as ex:
pass
# ---------------------------------------
# Utility Functions
# Dynamically load win32api on demand
# Install with: pip install pywin32
win32api=winerror=win32event=None
def ensure_win32api():
global win32api,winerror,win32event
if win32api is None:
import win32api
import winerror
import win32event
# Dynamically load fcntl on demand
# Install with: pip install fcntl
fcntl=None
def ensure_fcntl():
global fcntl
if fcntl is None:
import fcntl
def isWin():
return (os.name == 'nt')
# ---------------------------------------
Here is it in use:
import time, sys
def main(argv):
_timeout = 10
print("main() called. sleeping for %s seconds" % _timeout)
time.sleep(_timeout)
print("DONE")
if __name__ == '__main__':
SCR_NAME = "my_script"
sic = SingleInstanceChecker(SCR_NAME)
if sic.already_running():
print("An instance of {} is already running.".format(SCR_NAME))
sys.exit(1)
else:
main(sys.argv[1:])
I use single_process on my gentoo;
pip install single_process
example:
from single_process import single_process
#single_process
def main():
print 1
if __name__ == "__main__":
main()
refer: https://pypi.python.org/pypi/single_process/
I keep suspecting there ought to be a good POSIXy solution using process groups, without having to hit the file system, but I can't quite nail it down. Something like:
On startup, your process sends a 'kill -0' to all processes in a particular group. If any such processes exist, it exits. Then it joins the group. No other processes use that group.
However, this has a race condition - multiple processes could all do this at precisely the same time and all end up joining the group and running simultaneously. By the time you've added some sort of mutex to make it watertight, you no longer need the process groups.
This might be acceptable if your process only gets started by cron, once every minute or every hour, but it makes me a bit nervous that it would go wrong precisely on the day when you don't want it to.
I guess this isn't a very good solution after all, unless someone can improve on it?
I ran into this exact problem last week, and although I did find some good solutions, I decided to make a very simple and clean python package and uploaded it to PyPI. It differs from tendo in that it can lock any string resource name. Although you could certainly lock __file__ to achieve the same effect.
Install with: pip install quicklock
Using it is extremely simple:
[nate#Nates-MacBook-Pro-3 ~/live] python
Python 2.7.6 (default, Sep 9 2014, 15:04:36)
[GCC 4.2.1 Compatible Apple LLVM 6.0 (clang-600.0.39)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from quicklock import singleton
>>> # Let's create a lock so that only one instance of a script will run
...
>>> singleton('hello world')
>>>
>>> # Let's try to do that again, this should fail
...
>>> singleton('hello world')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/Users/nate/live/gallery/env/lib/python2.7/site-packages/quicklock/quicklock.py", line 47, in singleton
raise RuntimeError('Resource <{}> is currently locked by <Process {}: "{}">'.format(resource, other_process.pid, other_process.name()))
RuntimeError: Resource <hello world> is currently locked by <Process 24801: "python">
>>>
>>> # But if we quit this process, we release the lock automatically
...
>>> ^D
[nate#Nates-MacBook-Pro-3 ~/live] python
Python 2.7.6 (default, Sep 9 2014, 15:04:36)
[GCC 4.2.1 Compatible Apple LLVM 6.0 (clang-600.0.39)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from quicklock import singleton
>>> singleton('hello world')
>>>
>>> # No exception was thrown, we own 'hello world'!
Take a look: https://pypi.python.org/pypi/quicklock
linux example
This method is based on the creation of a temporary file automatically deleted after you close the application.
the program launch we verify the existence of the file;
if the file exists ( there is a pending execution) , the program is closed ; otherwise it creates the file and continues the execution of the program.
from tempfile import *
import time
import os
import sys
f = NamedTemporaryFile( prefix='lock01_', delete=True) if not [f for f in os.listdir('/tmp') if f.find('lock01_')!=-1] else sys.exit()
YOUR CODE COMES HERE
On a Linux system one could also ask
pgrep -a for the number of instances, the script
is found in the process list (option -a reveals the
full command line string). E.g.
import os
import sys
import subprocess
procOut = subprocess.check_output( "/bin/pgrep -u $UID -a python", shell=True,
executable="/bin/bash", universal_newlines=True)
if procOut.count( os.path.basename(__file__)) > 1 :
sys.exit( ("found another instance of >{}<, quitting."
).format( os.path.basename(__file__)))
Remove -u $UID if the restriction should apply to all users.
Disclaimer: a) it is assumed that the script's (base)name is unique, b) there might be race conditions.
Here's a good example for django with contextmanager and memcached:
https://docs.celeryproject.org/en/latest/tutorials/task-cookbook.html
Can be used to protect simultaneous operation on different hosts.
Can be used to manage multiple tasks.
Can also be changed for simple python scripts.
My modification of the above code is here:
import time
from contextlib import contextmanager
from django.core.cache import cache
#contextmanager
def memcache_lock(lock_key, lock_value, lock_expire):
timeout_at = time.monotonic() + lock_expire - 3
# cache.add fails if the key already exists
status = cache.add(lock_key, lock_value, lock_expire)
try:
yield status
finally:
# memcache delete is very slow, but we have to use it to take
# advantage of using add() for atomic locking
if time.monotonic() < timeout_at and status:
# don't release the lock if we exceeded the timeout
# to lessen the chance of releasing an expired lock owned by someone else
# also don't release the lock if we didn't acquire it
cache.delete(lock_key)
LOCK_EXPIRE = 60 * 10 # Lock expires in 10 minutes
def main():
lock_name, lock_value = "lock_1", "locked"
with memcache_lock(lock_name, lock_value, LOCK_EXPIRE) as acquired:
if acquired:
# single instance code here:
pass
if __name__ == "__main__":
main()
Here is a cross-platform implementation, creating a temporary lock file using a context manager.
Can be used to manage multiple tasks.
import os
from contextlib import contextmanager
from time import sleep
class ExceptionTaskInProgress(Exception):
pass
# Context manager for suppressing exceptions
class SuppressException:
def __init__(self):
pass
def __enter__(self):
return self
def __exit__(self, *exc):
return True
# Context manager for task
class TaskSingleInstance:
def __init__(self, task_name, lock_path):
self.task_name = task_name
self.lock_path = lock_path
self.lock_filename = os.path.join(self.lock_path, self.task_name + ".lock")
if os.path.exists(self.lock_filename):
raise ExceptionTaskInProgress("Resource already in use")
def __enter__(self):
self.fl = open(self.lock_filename, "w")
return self
def __exit__(self, exc_type, exc_val, exc_tb):
self.fl.close()
os.unlink(self.lock_filename)
# Here the task is silently interrupted
# if it is already running on another instance.
def main1():
task_name = "task1"
tmp_filename_path = "."
with SuppressException():
with TaskSingleInstance(task_name, tmp_filename_path):
print("The task `{}` has started.".format(task_name))
# The single task instance code is here.
sleep(5)
print("The task `{}` has completed.".format(task_name))
# Here the task is interrupted with a message
# if it is already running in another instance.
def main2():
task_name = "task1"
tmp_filename_path = "."
try:
with TaskSingleInstance(task_name, tmp_filename_path):
print("The task `{}` has started.".format(task_name))
# The single task instance code is here.
sleep(5)
print("Task `{}` completed.".format(task_name))
except ExceptionTaskInProgress as ex:
print("The task `{}` is already running.".format(task_name))
if __name__ == "__main__":
main1()
main2()
import sys,os
# start program
try: # (1)
os.unlink('lock') # (2)
fd=os.open("lock", os.O_CREAT|os.O_EXCL) # (3)
except:
try: fd=os.open("lock", os.O_CREAT|os.O_EXCL) # (4)
except:
print "Another Program running !.." # (5)
sys.exit()
# your program ...
# ...
# exit program
try: os.close(fd) # (6)
except: pass
try: os.unlink('lock')
except: pass
sys.exit()