hgweb: use separate repo instances per thread Before this change, multiple threads/requests could share a localrepository instance. This meant that all of localrepository needed to be thread safe. Many bugs have been reported telling us that localrepository isn't actually thread safe. While making localrepository thread safe is a noble cause, it is a lot of work. And there is little gain from doing so. Due to Python's GIL, only 1 thread may be processing Python code at a time. The benefits to multi-threaded servers are marginal. Thread safety would be a lot of work for little gain. So, we're not going to even attempt it. This patch establishes a pool of repos in hgweb. When a request arrives, we obtain the most recently used repository from the pool or create a new one if none is available. When the request has finished, we put that repo back in the pool. We start with a pool size of 1. For servers using a single thread, the pool will only ever be of size 1. For multi-threaded servers, the pool size will grow to the max number of simultaneous requests the server processes. No logic for pruning the pool has been implemented. We assume server operators either limit the number of threads to something they can handle or restart the Mercurial process after a certain amount of requests or time has passed.

hg: establish a cache for localrepository instances hgweb contained code for determining whether a cached localrepository instance was up to date. This code was way too low-level to be in hgweb. This functionality has been moved to a new "cachedlocalrepo" class in hg.py. The code has been changed slightly to facilitate use inside a class. hgweb has been refactored to use the new API. As part of this refactor, hgweb.repo no longer exists! We're very close to using a distinct repo instance per thread. The new cache records state when it is created. This intelligence prevents an extra localrepository from being created on the first hgweb request. This is why some redundant output from test-extension.t has gone away.

hgweb: create function to perform actions on new repo We perform some common tasks when a new repo instance is obtained. In preparation for changing how we obtain repo instances, factor this functionality into a standalone function.

hgweb: remove proxy to hgweb instance We were temporarily routing attributes until all request-specific attributes from hgweb were moved to requestcontext. We have finally reached that juncture and we can remove the proxy. At this point, only the repo instance is prone to race conditions between threads. This will be dealt with shortly.

dispatch: disable demandimport when invoking the debugger Turns out that demandimport confuses pudb, which does some pretty complicated imports. I think it's reasonable to disable demandimport here.

templater: create string unescape helper (issue4798) This gives us a unified place to do error-handling of string-escaping syntax errors

parsers: use PyTuple_New and SET_ITEM to construct metadata pair of markers With these 2 patches, fm1readmarkers() gets slightly faster: obsolete._fm1readmarkers() for 78644 entries 58.0 -> 56.2msec