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Contents
module ThreadSafe
class MriCacheBackend < NonConcurrentCacheBackend
# We can get away with a single global write lock (instead of a per-instance one) because of the GVL/green threads.
#
# The previous implementation used `Thread.critical` on 1.8 MRI to implement the 4 composed atomic operations (`put_if_absent`, `replace_pair`,
# `replace_if_exists`, `delete_pair`) this however doesn't work for `compute_if_absent` because on 1.8 the Mutex class is itself implemented
# via `Thread.critical` and a call to `Mutex#lock` does not restore the previous `Thread.critical` value (thus any synchronisation clears the
# `Thread.critical` flag and we loose control). This poses a problem as the provided block might use synchronisation on its own.
#
# NOTE: a neat idea of writing a c-ext to manually perform atomic put_if_absent, while relying on Ruby not releasing a GVL while calling
# a c-ext will not work because of the potentially Ruby implemented `#hash` and `#eql?` key methods.
WRITE_LOCK = Mutex.new
def []=(key, value)
WRITE_LOCK.synchronize { super }
end
def compute_if_absent(key)
if stored_value = _get(key) # fast non-blocking path for the most likely case
stored_value
else
WRITE_LOCK.synchronize { super }
end
end
def compute_if_present(key)
WRITE_LOCK.synchronize { super }
end
def compute(key)
WRITE_LOCK.synchronize { super }
end
def merge_pair(key, value)
WRITE_LOCK.synchronize { super }
end
def replace_pair(key, old_value, new_value)
WRITE_LOCK.synchronize { super }
end
def replace_if_exists(key, new_value)
WRITE_LOCK.synchronize { super }
end
def get_and_set(key, value)
WRITE_LOCK.synchronize { super }
end
def delete(key)
WRITE_LOCK.synchronize { super }
end
def delete_pair(key, value)
WRITE_LOCK.synchronize { super }
end
def clear
WRITE_LOCK.synchronize { super }
end
end
end
Version data entries
10 entries across 10 versions & 3 rubygems