BUG Use /tmp for joblib temp files instead of /shm (#37)

Instruct joblib to use disk for temporary files. Joblib defaults to /shm when that directory is present. In the Docker container, /shm is present but defaults to 64 MB. That's not enough space to handle even moderate-sized computations. The temporary directory is a bit slower, but has much more space.

 https://github.com/joblib/joblib/blob/0.11/joblib/parallel.py#L328L342

CHANGELOG.md

@@ -9,6 +9,10 @@ Version number changes (major.minor.micro) in this package denote the following:
 
 ## Unreleased
 
+### Fixes
+- Use /tmp for joblib temporary files instead of /shm
+
+
 ## [3.0.1] - 2017-05-25
 ### Package Updates
 - muffnn 1.1.1 -> 1.1.2

Dockerfile

@@ -92,6 +92,12 @@ RUN mkdir -p ${HOME}/.config/matplotlib && \
     echo "backend      : Agg" > ${HOME}/.config/matplotlib/matplotlibrc && \
     python -c "import matplotlib.pyplot"
 
+# Instruct joblib to use disk for temporary files. Joblib defaults to
+# /shm when that directory is present. In the Docker container, /shm is
+# present but defaults to 64 MB.
+# https://github.com/joblib/joblib/blob/0.11/joblib/parallel.py#L328L342
+ENV JOBLIB_TEMP_FOLDER=/tmp
+
 ENV VERSION=3.0.1 \
     VERSION_MAJOR=3 \
     VERSION_MINOR=0 \

README.md

@@ -57,6 +57,15 @@ VERSION_MICRO
 VERSION contains the full version string, e.g. "1.0.3". VERSION_MAJOR,
 VERSION_MINOR, and VERSION_MICRO each contain a single integer.
 
+## Joblib Temporary Files
+
+The [`joblib`](https://pythonhosted.org/joblib/) library enhances multiprocessing
+capabilities for scientific Python computing. In particular, the `scikit-learn`
+library uses `joblib` for parallelization. This Docker image sets `joblib`'s
+default location for staging temporary files to the /tmp directory.
+The normal default is /shm. /shm is a RAM disk which defaults to a 64 MB size
+in Docker containers, too small for typical scientific computing.
+
 # Creating Equivalent Local Environments
 
 The `environment.yml` file in this repo can be used to create a python environment that is