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Example Code : Shared Memory with Mutex (pywin32 and ctypes)

Hello,
Here is some sample code with pywin32 build 203 and ctypes 0.9.6.

Best regards,
/Srijit

File: SharedMemCreate_Mutex_win32all.py

# This application should be used with SharedMemAccess_Mutex_ctypes.py
or SharedMemAccess_Mutex_win32all.py
#~ a) Creates a shared memory
#~ b) Creates or Opens a mutex
#~ c) Reads the contents (null terminated string) of shared memory
#~ d) Acquires a mutex and then writes a null terminated string to the
shared memory
#~ e) Sleeps upto 2 seconds. Sleep time is generated by a random number
#~ f) Repeats steps (c), (d) and (e) indefintely

import mmap, random, time
import win32event, pywintypes, win32api

def main():
SHMEMSIZE = 256

ERROR_ALREADY_EXISTS = 183

szName = "MyFileMappingObject"
szMsg1 = "Message from first process using win32all and mmap - "
szMutex = "MyMutexObject"

shmem = mmap.mmap(0, SHMEMSIZE, szName, mmap.ACCESS_WRITE)

try:
hMutex = win32event.CreateMutex(None, pywintypes.FALSE,
szMutex)
if (win32api.GetLastError() == ERROR_ALREADY_EXISTS):
print"Opened existing mutex object", szMutex
else:
print "Created new mutex"

i=0
random.seed()
while 1:
szMsg1 = szMsg1 + hex(i) + "\0"
if (len(szMsg1) > SHMEMSIZE):
print "Current size of string message is", len(szMsg1),
"and greater than", SHMEMSIZE
break
shmem_read = shmem.read(SHMEMSIZE)
shmem_read = shmem_read.rstrip(chr(0))
shmem_read = shmem_read.rstrip(" ")
print "RECEIVED from SECOND Process: ", shmem_read
shmem.seek(0)
wait_result = win32event.WaitForSingleObject(hMutex, 1000)
if (wait_result == win32event.WAIT_OBJECT_0):
shmem.write(szMsg1)
while (shmem.tell() != SHMEMSIZE):
shmem.write_byte(" ")
shmem.seek(0)
print "WROTE in FIRST process: ", szMsg1
win32event.ReleaseMutex(hMutex)
elif(wait_result == win32event.WAIT_TIMEOUT):
print "COULD NOT ACQUIRE MUTEX. TIMEOUT OCCURED"
elif (wait_result == win32event.WAIT_ABONDONED):
print "WAIT ABANDONED"
i = i + 1
szMsg1 = "Message from first process using win32all and
mmap - "
time.sleep(random.random()*2)

except pywintypes.error, (errno, object, strerror):
print "Error in", object, ":", strerror

if __name__ == "__main__":
main()
File: SharedMemCreate_Mutex_ctypes.py

# This application should be used with SharedMemAccess_Mutex_ctypes.py
or SharedMemAccess_Mutex_win32all.py
#~ a) Creates a shared memory
#~ b) Creates or Opens a mutex
#~ c) Reads the contents (null terminated string) of shared memory
#~ d) Acquires a mutex and then writes a null terminated string to the
shared memory
#~ e) Sleeps upto 2 seconds. Sleep time is generated by a random number
#~ f) Repeats steps (c), (d) and (e) indefintely
# There are two options to implement this code - Option A or Option B.
If Option B(A) is chosen then
# Option A(B) should be commented.
import random, time
from ctypes import *

def main():
try:
SHMEMSIZE = 256

TRUE = 1
FALSE = 0
ERROR_ALREADY_EXISTS = 183
FILE_MAP_ALL_ACCESS = 0xF001F
WAIT_OBJECT_0 = 0
WAIT_TIMEOUT = 0x102
WAIT_ABANDONED = 0x80
PAGE_READWRITE = 0x04
INVALID_HANDLE_VALUE = 0xFFFFFFFF

szName = "MyFileMappingObject"
szMsg1 = "Message from first process using ctypes - "
szMutex = "MyMutexObject"

hMutex = windll.kernel32.CreateMutexA(None, FALSE, szMutex)
if (hMutex == 0):
raise WinError()
elif (windll.kernel32.GetLastError() == ERROR_ALREADY_EXISTS):
print"Opened existing mutex object", szMutex
else:
print "Created new mutex"

hMap = windll.kernel32.CreateFileMappingA(INVALID_HANDLE_ VALUE,
None, PAGE_READWRITE, 0, SHMEMSIZE, szName)
if (hMap == 0):
print "Could not open file mapping object"
raise WinError()

MapViewOfFile = windll.kernel32.MapViewOfFile
MapViewOfFile.restype = POINTER(c_char) # Option A
pBuf = MapViewOfFile(hMap, FILE_MAP_ALL_ACCESS, 0, 0, 0)
if (pBuf == 0):
raise WinError()

i=0
random.seed()
while 1:
szMsg1 = szMsg1 + hex(i) + "\0"
pBuf_str = cast(pBuf, c_char_p) # Option A
if (len(szMsg1) > SHMEMSIZE):
print "Current size of string message is", len(szMsg1),
"and greater than", SHMEMSIZE
break
print "RECEIVED from SECOND Process: ", pBuf_str.value #
Option A
#~ print "RECEIVED from SECOND Process: ", string_at(pBuf)
# Option B
wait_result = windll.kernel32.WaitForSingleObject(hMutex,
1000)
if (wait_result == WAIT_OBJECT_0):
memset(pBuf, ord(" "), SHMEMSIZE)
cdll.msvcrt.strcpy(pBuf_str, szMsg1) # Option A
#~ cdll.msvcrt.strcpy(pBuf, szMsg1) # Option B
print "WROTE in FIRST process: ", szMsg1
release_mutex = windll.kernel32.ReleaseMutex(hMutex)
if (release_mutex == 0):
print "CANNOT RELEASE ACQUIRED MUTEX"
elif(wait_result == WAIT_TIMEOUT):
print "COULD NOT ACQUIRE MUTEX. TIMEOUT OCCURED"
elif (wait_result == WAIT_ABONDONED):
print "WAIT ABANDONED"
i = i + 1
szMsg1 = "Message from first process using ctypes - "
time.sleep(random.random()*2)

windll.kernel32.UnmapViewOfFile(pBuf)
windll.kernel32.CloseHandle(hMap)
return
except WindowsError, (strerror):
print strerror
if (pBuf != 0):
windll.kernel32.UnmapViewOfFile(pBuf)
if (hMap != 0):
windll.kernel32.CloseHandle(hMap)
return

if __name__ == "__main__":
main()
File : SharedMemAccess_Mutex_win32all.py

# This application should be used with SharedMemCreate_Mutex_ctypes.py
or SharedMemCreate_Mutex_win32all.py
#~ a) Opens an existing shared memory
#~ b) Opens an existing mutex
#~ c) Reads the contents (null terminated string) of shared memory
#~ d) Acquires a mutex and then writes a null terminated string to the
shared memory
#~ e) Sleeps upto 2 seconds. Sleep time is generated by a random number
#~ f) Repeats steps (c), (d) and (e) indefintely

import mmap, random, time
import win32event, pywintypes

def main():
SHMEMSIZE = 256

STANDARD_RIGHTS_REQUIRED = 0xF0000
SYNCHRONIZE = 0x100000
MUTANT_QUERY_STATE = 0x1

MUTEX_ALL_ACCESS = STANDARD_RIGHTS_REQUIRED | SYNCHRONIZE |
MUTANT_QUERY_STATE

szName = "MyFileMappingObject"
szMsg1 = "Message from second process using win32all and mmap - "
szMutex = "MyMutexObject"

shmem = mmap.mmap(0, SHMEMSIZE, szName, mmap.ACCESS_WRITE)
try:
hMutex = win32event.OpenMutex(MUTEX_ALL_ACCESS,
pywintypes.FALSE, szMutex)
print"Opened existing mutex object", szMutex
i = 0;
random.seed()
while 1:
szMsg1 = szMsg1 + hex(i) + "\0"
if (len(szMsg1) > SHMEMSIZE):
print "Current size of string message is", len(szMsg1),
"and greater than", SHMEMSIZE
break
shmem_read = shmem.read(SHMEMSIZE)
shmem_read = shmem_read.rstrip(chr(0))
shmem_read = shmem_read.rstrip(" ")
print "RECEIVED from FIRST Process: ", shmem_read
shmem.seek(0)
wait_result = win32event.WaitForSingleObject(hMutex, 1000)
if (wait_result == win32event.WAIT_OBJECT_0):
shmem.write(szMsg1)
while (shmem.tell() != SHMEMSIZE):
shmem.write_byte(" ")
shmem.seek(0)
print "WROTE in SECOND process: ", szMsg1
win32event.ReleaseMutex(hMutex)
elif(wait_result == win32event.WAIT_TIMEOUT):
print "COULD NOT ACQUIRE MUTEX. TIMEOUT OCCURED"
elif (wait_result == win32event.WAIT_ABONDONED):
print "WAIT ABANDONED"
i = i + 1
szMsg1 = "Message from second process using win32all and
mmap - "
time.sleep(random.random()*2)
except pywintypes.error, (errno, object, strerror):
print "Error in", object, ":", strerror

shmem.close()
return
if __name__ == "__main__":
main()
File: SharedMemAccess_Mutex_ctypes.py

# This application should be used with SharedMemCreate_Mutex_ctypes.py
or SharedMemCreate_Mutex_win32all.py
#~ a) Opens an existing shared memory
#~ b) Opens an existing mutex
#~ c) Reads the contents (null terminated string) of shared memory
#~ d) Acquires a mutex and then writes a null terminated string to the
shared memory
#~ e) Sleeps upto 2 seconds. Sleep time is generated by a random number
#~ f) Repeats steps (c), (d) and (e) indefintely
# There are two options to implement this code - Option A or Option B.
If Option B(A) is chosen then
# Option A(B) should be commented.
import random, time
from ctypes import *

def main():

SHMEMSIZE = 256

FILE_MAP_ALL_ACCESS = 0xF001F
STANDARD_RIGHTS_REQUIRED = 0xF0000
SYNCHRONIZE = 0x100000
MUTANT_QUERY_STATE = 0x1
MUTEX_ALL_ACCESS = STANDARD_RIGHTS_REQUIRED | SYNCHRONIZE |
MUTANT_QUERY_STATE
WAIT_OBJECT_0 = 0
WAIT_TIMEOUT = 0x102
WAIT_ABANDONED = 0x80
TRUE = 1
FALSE = 0

szName = "MyFileMappingObject"
szMsg1 = "Message from second process using ctypes - "
szMutex = "MyMutexObject"

hMap = 0
pBuf = 0
hMutex = 0

try:
hMap = windll.kernel32.OpenFileMappingA(FILE_MAP_ALL_ACCE SS,
FALSE, szName)
if (hMap == 0):
raise WinError()

MapViewOfFile = windll.kernel32.MapViewOfFile
MapViewOfFile.restype = POINTER(c_char) # Option A
pBuf = MapViewOfFile(hMap, FILE_MAP_ALL_ACCESS, 0, 0, 0)
if (pBuf == 0):
raise WinError()

hMutex = windll.kernel32.OpenMutexA(MUTEX_ALL_ACCESS, FALSE,
szMutex)
if (hMutex == 0):
raise WinError()
else:
print"Opened existing mutex object", szMutex

i=0
random.seed()
while 1:
szMsg1 = szMsg1 + hex(i) + "\0"
pBuf_str = cast(pBuf, c_char_p) # Option A
if (len(szMsg1) > SHMEMSIZE):
print "Current size of string message is", len(szMsg1),
"and greater than", SHMEMSIZE
break
print "RECEIVED from FIRST Process: ", pBuf_str.value #
Option A
#~ print "RECEIVED from FIRST Process: ", string_at(pBuf) #
Option B
wait_result = windll.kernel32.WaitForSingleObject(hMutex,
1000)
if (wait_result == WAIT_OBJECT_0):
memset(pBuf, ord(" "), SHMEMSIZE)
cdll.msvcrt.strcpy(pBuf_str, szMsg1) # Option A
#~ cdll.msvcrt.strcpy(pBuf, szMsg1) # Option B
print "WROTE in SECOND process: ", szMsg1
release_mutex = windll.kernel32.ReleaseMutex(hMutex)
if (release_mutex == 0):
print "CANNOT RELEASE ACQUIRED MUTEX"
elif(wait_result == WAIT_TIMEOUT):
print "COULD NOT ACQUIRE MUTEX. TIMEOUT OCCURED"
elif (wait_result == WAIT_ABONDONED):
print "WAIT ABANDONED"
i = i + 1
szMsg1 = "Message from second process using ctypes - "
time.sleep(random.random()*2)

windll.kernel32.UnmapViewOfFile(pBuf)
windll.kernel32.CloseHandle(hMap)
return
except WindowsError, (strerror):
print strerror
if (pBuf != 0):
windll.kernel32.UnmapViewOfFile(pBuf)
if (hMap != 0):
windll.kernel32.CloseHandle(hMap)
return

if __name__ == "__main__":
main()

Jul 18 '05 #1
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