mirror of https://github.com/BOINC/boinc.git
110 lines
3.2 KiB
PHP
110 lines
3.2 KiB
PHP
<?php
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require_once("docutil.php");
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page_head("Core/app interaction (basic)");
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echo "
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INCOMPLETE AND OUT OF DATE
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<p>
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Explain startup files
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<p>
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Explain shared memory mechanism in general
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<p>
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Explain work-related use of shmem
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<p>
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Application are executed in separate 'catbox' directories,
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allowing them to create and use temporary files without name conflicts.
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Input and output files are kept outside the catbox.
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The mappings from virtual to physical filenames use
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'symbolic link' files in the catbox directory.
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The name of such a file is the virtual name,
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and the file contains an XML tag with the physical name.
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(This scheme is used because of the lack of filesystem links in Windows.)
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<p>
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Communication between the core client and applications
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is done through XML files in the catbox directory.
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Several files are used.
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<p>
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<b>Files created by the core client, read by the app:</b>
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(Once, at start of app)
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<ul>
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<li> Symbolic link files
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<li> <b>init_data.xml</b>: this contains the initialization data
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returned by <tt>boinc_init()</tt> (see above),
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as well as the minimum checkpoint period.
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</ul>
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<p>
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<b>Files created by the API implementation, read by the core client:</b>
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<ul>
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<li>
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<b>fraction_done.xml</b>:
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contains the WU fraction done and the current CPU time from start of WU.
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Written by the timer routine as needed.
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<li>
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<b>checkpoint_cpu.xml</b>
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CPU time (from start of WU) at last checkpoint.
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Written by checkpoint_completed.
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</ul>
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<p>
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The API implementation uses a timer (60Hz);
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the real-time clock is not available to applications.
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This timer is used for several purposes:
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<ul>
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<li> To tell the app when to checkpoint;
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<li> To regenerate the fraction done file
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<li> To refresh graphics
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</ul>
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<p>
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<b>Exit status</b>
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The core client does a wait() to get the status.
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boinc_finish() ends with an exit(status);
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<p>
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<b>Accounting of CPU time</b>:
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(note: in Unix, a parent can't get the CPU time of a child
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until the child exits. So we're forced to measure it in the child.)
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The core passes the WU CPU time in init_data.xml.
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boinc_checkpoint_completed() and boinc_finish() compute the new WU CPU time,
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and write it to checkpoint_cpu.xml.
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The core deletes this after reading.
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If on exit there is no checkpoint_cpu.xml, it means the app
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called exit(0) rather than boinc_finish().
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In this case the core measures the child CPU itself.
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<p>
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The core client maintains
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<p>
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<b>Timing of checkpoints</b>
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<p>
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The app library maintains time_until_checkpoint,
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decremented from the timer handler.
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boinc_time_to_checkpoint() returns nonzero if
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time_until_checkpoint is zero or less.
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boinc_checkpoint_completed() resets it.
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<p>
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<b>Maintaining fraction done and current CPU</b>
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<p>
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These two quantities are transferred from the app library to
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the core client in the file fraction_done.xml.
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The parameter <tt>time_until_fraction_done_update</tt>,
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passed in the initialization file,
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determines how often this file is written.
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It is written from the timer handler.
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<p>
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For multi-program applications, only the active application
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must write the file.
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The functions boinc_child_start() and boinc_child_done()
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tell the app library to stop and start writing the file.
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<p>
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TO DO: this creates disk traffic.
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Either figure out a way of increasing the period for users who don't
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want disk access, or don't use disk files.
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";
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page_tail();
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?>
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