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"""Implement a client cache
The cache is managed as two files, var/c0.zec and var/c1.zec.
Each cache file is a sequence of records of the form:
oid -- 8-byte object id
status -- 1-byte status v': valid, 'n': non-version valid, 'i': invalid
tlen -- 4-byte (unsigned) record length
vlen -- 2-bute (unsigned) version length
dlen -- 4-byte length of non-version data
serial -- 8-byte non-version serial (timestamp)
data -- non-version data
version -- Version string (if vlen > 0)
vdlen -- 4-byte length of version data (if vlen > 0)
vdata -- version data (if vlen > 0)
vserial -- 8-byte version serial (timestamp)
tlen -- 4-byte (unsigned) record length (for redundancy and backward
traversal)
There is a cache size limit.
The cache is managed as follows:
- Data are written to file 0 until file 0 exceeds limit/2 in size.
- Data are written to file 1 until file 1 exceeds limit/2 in size.
- File 0 is truncated to size 0 (or deleted and recreated).
- Data are written to file 0 until file 0 exceeds limit/2 in size.
- File 1 is truncated to size 0 (or deleted and recreated).
- Data are written to file 1 until file 1 exceeds limit/2 in size.
and so on.
On startup, index information is read from file 0 and file 1.
Current serial numbers are sent to the server for verification.
If any serial numbers are not valid, then the server will send back
invalidation messages and the cache entries will be invalidated.
When a cache record is invalidated, the data length is overwritten
with '\0\0\0\0'.
If var is not writable, then temporary files are used for
file 0 and file 1.
"""
__version__ = "$Revision: 1.5 $"[11:-2]
import os, tempfile
from struct import pack, unpack
magic='ZEC0'
class ClientCache:
def __init__(self, storage='', size=20000000, client=None, var=None):
if client:
if var is None: var=os.path.join(INSTANCE_HOME,'var')
self._p=p=map(lambda i, p=storage, var=var, c=client:
os.path.join(var,'c%s-%s-%s.zec' % (p, c, i)),
(0,1))
self._f=f=[None, None]
s=['\0\0\0\0\0\0\0\0', '\0\0\0\0\0\0\0\0']
for i in 0,1:
if os.path.exists(p[i]):
fi=open(p[i],'r+b')
if fi.read(4)==magic: # Minimal sanity
fi.seek(0,2)
if fi.tell() > 30:
fi.seek(22)
s[i]=fi.read(8)
if s[i]!='\0\0\0\0\0\0\0\0': f[i]=fi
fi=None
if s[1] > s[0]: current=1
elif s[0] > s[1]: current=0
else:
if f[0] is None:
f[0]=open(p[0], 'w+b')
f[0].write(magic)
current=0
f[1]=None
else:
self._p=p=map(
lambda i, p=storage:
tempfile.mktemp('.zec'),
(0,1))
self._f=f=[open(p[0],'w+b'), None]
f[0].write(magic)
current=0
self._limit=size/2
self._current=current
def open(self):
self._index=index={}
self._get=index.get
serial={}
f=self._f
current=self._current
if f[not current] is not None:
read_index(index, serial, f[not current], not current)
self._pos=read_index(index, serial, f[current], current)
return serial.items()
def invalidate(self, oid, version):
p=self._get(oid, None)
if p is None: return None
f=self._f[p < 0]
ap=abs(p)
f.seek(ap)
h=f.read(8)
if h != oid: return
f.write(version and 'n' or 'i')
def load(self, oid, version):
p=self._get(oid, None)
if p is None: return None
f=self._f[p < 0]
ap=abs(p)
seek=f.seek
read=f.read
seek(ap)
h=read(27)
if len(h)==27 and h[8] in 'nv' and h[:8]==oid:
tlen, vlen, dlen = unpack(">iHi", h[9:19])
else: tlen=-1
if tlen <= 0 or vlen < 0 or dlen <= 0 or vlen+dlen > tlen:
del self._index[oid]
return None
if version and h[8]=='n': return None
if not vlen or not version:
return read(dlen), h[19:]
seek(dlen, 1)
v=read(vlen)
if version != v:
seek(-dlen-vlen, 1)
return read(dlen), h[19:]
dlen=unpack(">i", read(4))[0]
return read(dlen), read(8)
def update(self, oid, serial, version, data):
if version:
# We need to find and include non-version data
p=self._get(oid, None)
if p is None: return None
f=self._f[p < 0]
ap=abs(p)
seek=f.seek
read=f.read
seek(ap)
h=read(27)
if len(h)==27 and h[8] in 'nv' and h[:8]==oid:
tlen, vlen, dlen = unpack(">iHi", h[9:19])
else: tlen=-1
if tlen <= 0 or vlen < 0 or dlen <= 0 or vlen+dlen > tlen:
del self._index[oid]
return None
p=read(dlen)
s=h[19:]
self.store(oid, p, s, version, data, serial)
else:
# Simple case, just store new data:
self.store(oid, data, serial, '', None, None)
def modifiedInVersion(self, oid):
p=self._get(oid, None)
if p is None: return None
f=self._f[p < 0]
ap=abs(p)
seek=f.seek
read=f.read
seek(ap)
h=read(27)
if len(h)==27 and h[8] in 'nv' and h[:8]==oid:
tlen, vlen, dlen = unpack(">iHi", h[9:19])
else: tlen=-1
if tlen <= 0 or vlen < 0 or dlen <= 0 or vlen+dlen > tlen:
del self._index[oid]
return None
if h[8]=='n': return None
if not vlen: return ''
seek(dlen, 1)
return read(vlen)
def store(self, oid, p, s, version, pv, sv):
tlen=31+len(p)
if version:
tlen=tlen+len(version)+12+len(pv)
vlen=len(version)
else:
vlen=0
pos=self._pos
current=self._current
if pos+tlen > self._limit:
current=not current
self._current=current
self._f[current]=open(self._p[current],'w+b')
self._f[current].write(magic)
self._pos=pos=4
f=self._f[current]
f.seek(pos)
stlen=pack(">I",tlen)
write=f.write
write(oid+'v'+stlen+pack(">HI", vlen, len(p))+s)
write(p)
if version:
write(pack(">I", len(pv)))
write(pv)
write(sv+stlen)
if current: self._index[oid]=-pos
else: self._index[oid]=pos
self._pos=pos+tlen
def read_index(index, serial, f, current):
seek=f.seek
read=f.read
pos=4
seek(0,2)
size=f.tell()
while 1:
f.seek(pos)
h=read(27)
if len(h)==27 and h[8] in 'vni':
tlen, vlen, dlen = unpack(">iHi", h[9:19])
else: tlen=-1
if tlen <= 0 or vlen < 0 or dlen <= 0 or vlen+dlen > tlen:
break
oid=h[:8]
if h[8]=='v' and vlen:
seek(dlen+vlen, 1)
vdlen=read(4)
if len(vdlen) != 4: break
vdlen=unpack(">i", vdlen)[0]
if vlen+dlen+42+vdlen > tlen: break
seek(vdlen, 1)
vs=read(8)
if read(4) != h[9:13]: break
else: vs=None
if h[8] in 'vn':
if current: index[oid]=-pos
else: index[oid]=pos
serial[oid]=h[-8:], vs
else:
if serial.has_key(oid):
# We has a record for this oid, but it was invalidated!
del serial[oid]
del index[oid]
pos=pos+tlen
f.seek(pos)
try: f.truncate()
except: pass
return pos