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__revision__ = "src/engine/SCons/CacheDir.py 5134 2010/08/16 23:02:40 bdeegan"

__doc__ = """
CacheDir support
"""

import os.path
import stat
import sys

import SCons.Action

cache_enabled = True
cache_debug = False
cache_force = False
cache_show = False

def CacheRetrieveFunc(target, source, env):
    t = target[0]
    fs = t.fs
    cd = env.get_CacheDir()
    cachedir, cachefile = cd.cachepath(t)
    if not fs.exists(cachefile):
        cd.CacheDebug('CacheRetrieve(%s):  %s not in cache\n', t, cachefile)
        return 1
    cd.CacheDebug('CacheRetrieve(%s):  retrieving from %s\n', t, cachefile)
    if SCons.Action.execute_actions:
        if fs.islink(cachefile):
            fs.symlink(fs.readlink(cachefile), t.path)
        else:
            env.copy_from_cache(cachefile, t.path)
        st = fs.stat(cachefile)
        fs.chmod(t.path, stat.S_IMODE(st[stat.ST_MODE]) | stat.S_IWRITE)
    return 0

def CacheRetrieveString(target, source, env):
    t = target[0]
    fs = t.fs
    cd = env.get_CacheDir()
    cachedir, cachefile = cd.cachepath(t)
    if t.fs.exists(cachefile):
        return "Retrieved `%s' from cache" % t.path
    return None

CacheRetrieve = SCons.Action.Action(CacheRetrieveFunc, CacheRetrieveString)

CacheRetrieveSilent = SCons.Action.Action(CacheRetrieveFunc, None)

def CachePushFunc(target, source, env):
    t = target[0]
    if t.nocache:
        return
    fs = t.fs
    cd = env.get_CacheDir()
    cachedir, cachefile = cd.cachepath(t)
    if fs.exists(cachefile):
        # Don't bother copying it if it's already there.  Note that
        # usually this "shouldn't happen" because if the file already
        # existed in cache, we'd have retrieved the file from there,
        # not built it.  This can happen, though, in a race, if some
        # other person running the same build pushes their copy to
        # the cache after we decide we need to build it but before our
        # build completes.
        cd.CacheDebug('CachePush(%s):  %s already exists in cache\n', t, cachefile)
        return

    cd.CacheDebug('CachePush(%s):  pushing to %s\n', t, cachefile)

    tempfile = cachefile+'.tmp'+str(os.getpid())
    errfmt = "Unable to copy %s to cache. Cache file is %s"

    if not fs.isdir(cachedir):
        try:
            fs.makedirs(cachedir)
        except EnvironmentError:
            # We may have received an exception because another process
            # has beaten us creating the directory.
            if not fs.isdir(cachedir):
                msg = errfmt % (str(target), cachefile)
                raise SCons.Errors.EnvironmentError(msg)

    try:
        if fs.islink(t.path):
            fs.symlink(fs.readlink(t.path), tempfile)
        else:
            fs.copy2(t.path, tempfile)
        fs.rename(tempfile, cachefile)
        st = fs.stat(t.path)
        fs.chmod(cachefile, stat.S_IMODE(st[stat.ST_MODE]) | stat.S_IWRITE)
    except EnvironmentError:
        # It's possible someone else tried writing the file at the
        # same time we did, or else that there was some problem like
        # the CacheDir being on a separate file system that's full.
        # In any case, inability to push a file to cache doesn't affect
        # the correctness of the build, so just print a warning.
        msg = errfmt % (str(target), cachefile)
        SCons.Warnings.warn(SCons.Warnings.CacheWriteErrorWarning, msg)

CachePush = SCons.Action.Action(CachePushFunc, None)

class CacheDir(object):

    def __init__(self, path):
        try:
            import hashlib
        except ImportError:
            msg = "No hashlib or MD5 module available, CacheDir() not supported"
            SCons.Warnings.warn(SCons.Warnings.NoMD5ModuleWarning, msg)
            self.path = None
        else:
            self.path = path
        self.current_cache_debug = None
        self.debugFP = None

    def CacheDebug(self, fmt, target, cachefile):
        if cache_debug != self.current_cache_debug:
            if cache_debug == '-':
                self.debugFP = sys.stdout
            elif cache_debug:
                self.debugFP = open(cache_debug, 'w')
            else:
                self.debugFP = None
            self.current_cache_debug = cache_debug
        if self.debugFP:
            self.debugFP.write(fmt % (target, os.path.split(cachefile)[1]))

    def is_enabled(self):
        return (cache_enabled and not self.path is None)

    def cachepath(self, node):
        """
        """
        if not self.is_enabled():
            return None, None

        sig = node.get_cachedir_bsig()
        subdir = sig[0].upper()
        dir = os.path.join(self.path, subdir)
        return dir, os.path.join(dir, sig)

    def retrieve(self, node):
        """
        This method is called from multiple threads in a parallel build,
        so only do thread safe stuff here. Do thread unsafe stuff in
        built().

        Note that there's a special trick here with the execute flag
        (one that's not normally done for other actions).  Basically
        if the user requested a no_exec (-n) build, then
        SCons.Action.execute_actions is set to 0 and when any action
        is called, it does its showing but then just returns zero
        instead of actually calling the action execution operation.
        The problem for caching is that if the file does NOT exist in
        cache then the CacheRetrieveString won't return anything to
        show for the task, but the Action.__call__ won't call
        CacheRetrieveFunc; instead it just returns zero, which makes
        the code below think that the file *was* successfully
        retrieved from the cache, therefore it doesn't do any
        subsequent building.  However, the CacheRetrieveString didn't
        print anything because it didn't actually exist in the cache,
        and no more build actions will be performed, so the user just
        sees nothing.  The fix is to tell Action.__call__ to always
        execute the CacheRetrieveFunc and then have the latter
        explicitly check SCons.Action.execute_actions itself.
        """
        if not self.is_enabled():
            return False

        env = node.get_build_env()
        if cache_show:
            if CacheRetrieveSilent(node, [], env, execute=1) == 0:
                node.build(presub=0, execute=0)
                return True
        else:
            if CacheRetrieve(node, [], env, execute=1) == 0:
                return True

        return False

    def push(self, node):
        if not self.is_enabled():
            return
        return CachePush(node, [], node.get_build_env())

    def push_if_forced(self, node):
        if cache_force:
            return self.push(node)

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