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POErlang file truncation
 

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    <p>I'm trying to write a basic Erlang program that reads in a file in one process and writes the file in another process. I'm finding that sometimes the output file gets truncated.</p> <p>For instance I wrote eunit test. If I run the single test <strong>drive_test:write_file_test()</strong> the output is correctly written. But running <strong>drive_test:test()</strong> truncates the output file in a different place each time. </p> <p>Do I need to do something special to make sure that the process finishes writing before it closes?</p> <p>drive.erl:</p> <pre><code>-module(drive). -include("library.hrl"). -export([init/1]). init(Drive) -&gt; loop(Drive). loop(Drive) -&gt; receive {write, Data} -&gt; write(Drive,Data), loop(Drive); close -&gt; close(Drive) end. write(Drive,Data) -&gt; %io:format("~p", [Data]), Handler = Drive#drive.volume, file:write(Handler, [Data]). close(Drive) -&gt; Handler = Drive#drive.volume, file:close(Handler), io:format("closed ~w~n", [Drive]). </code></pre> <p>drive_test.erl</p> <pre><code>-module(drive_test). -include_lib("eunit/include/eunit.hrl"). -include("library.hrl"). startupShutdown_test() -&gt; DrivePid = spawn(drive,init,[#drive{number=1}]), DrivePid ! close. write_basic_test() -&gt; {ok, F} =file:open("test/library/eunit.txt", write), DrivePid = spawn(drive,init,[#drive{number=1,volume=F}]), DrivePid ! {write, "Some Data"}, DrivePid ! close. write_file_test() -&gt; {ok, Fin} = file:open("cathedral.pdf", read), {ok, Fout} =file:open("test/library/eunit2.txt", write), DrivePid = spawn(drive,init,[#drive{number=1,volume=Fout}]), write_file( Fin, DrivePid), DrivePid ! close. write_file(F, DrivePid ) -&gt; Rd = file:read(F, 256), case Rd of {ok, Data} -&gt; DrivePid ! {write, Data}, write_file(F, DrivePid ); eof -&gt; file:close(F); _ -&gt; ?_assert(false) end. </code></pre> <p>truncated file:</p> <pre><code>$ ls -l cathedral.pdf test/library/eunit2.txt -rwx------+ 1 218879 Sep 16 22:21 cathedral.pdf -rwxr-xr-x 1 60928 Dec 17 09:31 test/library/eunit2.txt </code></pre>
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