adding h5e_get_auto wrapper for error handling manipulation

[getzdan]

HDF5 outputs a lot of DIAG messages. they can be turned off with:

   HDF5.h5e_set_auto(HDF5.H5E_DEFAULT, C_NULL, C_NULL)

nice, but if one wants to turn DIAG back on she needs the original error handlers.
to get those you can use h5e_get_auto. which can be wrapped in HDF5 with the following change:

   diff --git a/src/plain.jl b/src/plain.jl
   index 7c58932..ee857a9 100644
   --- a/src/plain.jl
   +++ b/src/plain.jl
         (:h5d_write, :H5Dwrite, Herr, (Hid, Hid, Hid, Hid, Hid, Ptr{Void}), (:dataset_id, :mem_type_id, :mem_space_id, :file_space_id
   +     (:h5e_get_auto, :H5Eget_auto2, Herr, (Hid, Ptr{Ptr{Void}},Ptr{Ptr{Void}}), (:estack_id, :func, :client_data), "Error getting 
         (:h5e_set_auto, :H5Eset_auto2, Herr, (Hid, Ptr{Void}, Ptr{Void}), (:estack_id, :func, :client_data), "Error setting error rep

then, turn off/on messages can be accomplished with:

   hdf5errorfunc = Array(Ptr{Void},1)
   hdf5errorprivdata = Array(Ptr{Void},1)
   # turn off messages
   res = HDF5.h5e_get_auto(HDF5.H5E_DEFAULT, hdf5errorfunc, hdf5errorprivdata)
   HDF5.h5e_set_auto(HDF5.H5E_DEFAULT, C_NULL, C_NULL)
   # turn on messages
   HDF5.h5e_set_auto(HDF5.H5E_DEFAULT, hdf5errorfunc[1], hdf5errorprivdata[1])

have little experience with turning things into pull requests, but can do so if I get a pull-request request.

[timholy]

Can you give us an example of the kind of error messages you want to suppress, and what the resulting output would be? I agree that the messages are long and ugly, but no messages would make debugging harder.

[getzdan]

When trying to open a non-existent file for example:

In  [12]: h5f = h5open("/ptmp/data/asdf.h5")
HDF5-DIAG: Error detected in HDF5 (1.8.11) thread 3059767040:
  #000: ../../../src/H5F.c line 858 in H5Fis_hdf5(): unable to open file
    major: Low-level I/O
    minor: Unable to initialize object
  #001: ../../../src/H5FD.c line 987 in H5FD_open(): open failed
    major: Virtual File Layer
    minor: Unable to initialize object
  #002: ../../../src/H5FDsec2.c line 343 in H5FD_sec2_open(): unable to open file: name = '/ptmp/data/asdf.h5', errno = 2, error message = 'No such file or directory', flags = 0, o_flags = 0
    major: File accessibilty
    minor: Unable to open file

Out [12]: ERROR: Cannot access file /ptmp/data/asdf.h5
while loading In[12], in expression starting on line 1
 in h5f_is_hdf5 at /home/dan/.julia/v0.4/HDF5/src/plain.jl:1944
 in h5open at /home/dan/.julia/v0.4/HDF5/src/plain.jl:513
 in h5open at /home/dan/.julia/v0.4/HDF5/src/plain.jl:523 (repeats 2 times)

The usefulness for debugging is exactly the reason I wanted an on/off ability for message suppression.

[timholy]

Are you proposing off by default, or on by default? We would also need a more convenient way of turning them back on. (Something where the user doesn't effectively have to know the libhdf5 API.)

As long as what you're proposing is merely an expansion of capabilities, then sure, it would be worth merging a PR.

[getzdan]

"on" by default is fine. a couple of functions for on/off toggling would be nice, especially in try/catch/finally blocks which are expected to generate errors occasionally.

currently, my only change was a one-liner in plain.jl (see above) and toggling is then possible (as described). a higher level API for this feature is a good idea.

[kleinhenz]

closed via #677.