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301 lines
11 KiB
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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN">
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<html>
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<head>
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<title>Code Review</title>
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</head>
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<body>
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<center><h1>Code Review 1</h1></center>
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<h3>Some background...</h3>
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<p>This is one of the functions exported from the
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<code>H5B.c</code> file that implements a B-link-tree class
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without worrying about concurrency yet (thus the `Note:' in the
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function prologue). The <code>H5B.c</code> file provides the
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basic machinery for operating on generic B-trees, but it isn't
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much use by itself. Various subclasses of the B-tree (like
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symbol tables or indirect storage) provide their own interface
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and back end to this function. For instance,
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<code>H5G_stab_find()</code> takes a symbol table OID and a name
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and calls <code>H5B_find()</code> with an appropriate
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<code>udata</code> argument that eventually gets passed to the
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<code>H5G_stab_find()</code> function.
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<p><code><pre>
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1 /*-------------------------------------------------------------------------
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2 * Function: H5B_find
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3 *
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4 * Purpose: Locate the specified information in a B-tree and return
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5 * that information by filling in fields of the caller-supplied
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6 * UDATA pointer depending on the type of leaf node
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7 * requested. The UDATA can point to additional data passed
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8 * to the key comparison function.
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9 *
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10 * Note: This function does not follow the left/right sibling
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11 * pointers since it assumes that all nodes can be reached
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12 * from the parent node.
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13 *
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14 * Return: Success: SUCCEED if found, values returned through the
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15 * UDATA argument.
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16 *
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17 * Failure: FAIL if not found, UDATA is undefined.
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18 *
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19 * Programmer: Robb Matzke
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20 * matzke@llnl.gov
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21 * Jun 23 1997
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22 *
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23 * Modifications:
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24 *
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25 *-------------------------------------------------------------------------
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26 */
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27 herr_t
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28 H5B_find (H5F_t *f, const H5B_class_t *type, const haddr_t *addr, void *udata)
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29 {
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30 H5B_t *bt=NULL;
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31 intn idx=-1, lt=0, rt, cmp=1;
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32 int ret_value = FAIL;
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</pre></code>
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<p>All pointer arguments are initialized when defined. I don't
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worry much about non-pointers because it's usually obvious when
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the value isn't initialized.
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<p><code><pre>
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33
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34 FUNC_ENTER (H5B_find, NULL, FAIL);
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35
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36 /*
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37 * Check arguments.
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38 */
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39 assert (f);
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40 assert (type);
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41 assert (type->decode);
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42 assert (type->cmp3);
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43 assert (type->found);
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44 assert (addr && H5F_addr_defined (addr));
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</pre></code>
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<p>I use <code>assert</code> to check invariant conditions. At
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this level of the library, none of these assertions should fail
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unless something is majorly wrong. The arguments should have
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already been checked by higher layers. It also provides
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documentation about what arguments might be optional.
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<p><code><pre>
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45
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46 /*
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47 * Perform a binary search to locate the child which contains
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48 * the thing for which we're searching.
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49 */
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50 if (NULL==(bt=H5AC_protect (f, H5AC_BT, addr, type, udata))) {
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51 HGOTO_ERROR (H5E_BTREE, H5E_CANTLOAD, FAIL);
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52 }
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</pre></code>
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<p>You'll see this quite often in the low-level stuff and it's
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documented in the <code>H5AC.c</code> file. The
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<code>H5AC_protect</code> insures that the B-tree node (which
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inherits from the H5AC package) whose OID is <code>addr</code>
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is locked into memory for the duration of this function (see the
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<code>H5AC_unprotect</code> on line 90). Most likely, if this
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node has been accessed in the not-to-distant past, it will still
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be in memory and the <code>H5AC_protect</code> is almost a
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no-op. If cache debugging is compiled in, then the protect also
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prevents other parts of the library from accessing the node
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while this function is protecting it, so this function can allow
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the node to be in an inconsistent state while calling other
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parts of the library.
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<p>The alternative is to call the slighlty cheaper
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<code>H5AC_find</code> and assume that the pointer it returns is
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valid only until some other library function is called, but
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since we're accessing the pointer throughout this function, I
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chose to use the simpler protect scheme. All protected objects
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<em>must be unprotected</em> before the file is closed, thus the
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use of <code>HGOTO_ERROR</code> instead of
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<code>HRETURN_ERROR</code>.
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<p><code><pre>
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53 rt = bt->nchildren;
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54
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55 while (lt<rt && cmp) {
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56 idx = (lt + rt) / 2;
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57 if (H5B_decode_keys (f, bt, idx)<0) {
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58 HGOTO_ERROR (H5E_BTREE, H5E_CANTDECODE, FAIL);
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59 }
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60
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61 /* compare */
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62 if ((cmp=(type->cmp3)(f, bt->key[idx].nkey, udata,
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63 bt->key[idx+1].nkey))<0) {
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64 rt = idx;
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65 } else {
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66 lt = idx+1;
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67 }
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68 }
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69 if (cmp) {
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70 HGOTO_ERROR (H5E_BTREE, H5E_NOTFOUND, FAIL);
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71 }
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</pre></code>
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<p>Code is arranged in paragraphs with a comment starting each
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paragraph. The previous paragraph is a standard binary search
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algorithm. The <code>(type->cmp3)()</code> is an indirect
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function call into the subclass of the B-tree. All indirect
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function calls have the function part in parentheses to document
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that it's indirect (quite obvious here, but not so obvious when
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the function is a variable).
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<p>It's also my standard practice to have side effects in
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conditional expressions because I can write code faster and it's
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more apparent to me what the condition is testing. But if I
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have an assignment in a conditional expr, then I use an extra
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set of parens even if they're not required (usually they are, as
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in this case) so it's clear that I meant <code>=</code> instead
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of <code>==</code>.
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<p><code><pre>
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72
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73 /*
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74 * Follow the link to the subtree or to the data node.
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75 */
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76 assert (idx>=0 && idx<bt->nchildren);
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77 if (bt->level > 0) {
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78 if ((ret_value = H5B_find (f, type, bt->child+idx, udata))<0) {
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79 HGOTO_ERROR (H5E_BTREE, H5E_NOTFOUND, FAIL);
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80 }
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81 } else {
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82 ret_value = (type->found)(f, bt->child+idx, bt->key[idx].nkey,
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83 udata, bt->key[idx+1].nkey);
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84 if (ret_value<0) {
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85 HGOTO_ERROR (H5E_BTREE, H5E_NOTFOUND, FAIL);
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86 }
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87 }
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</pre></code>
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<p>Here I broke the "side effect in conditional" rule, which I
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sometimes do if the expression is so long that the
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<code><0</code> gets lost at the end. Another thing to note is
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that success/failure is always determined by comparing with zero
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instead of <code>SUCCEED</code> or <code>FAIL</code>. I do this
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because occassionally one might want to return other meaningful
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values (always non-negative) or distinguish between various types of
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failure (always negative).
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<p><code><pre>
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88
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89 done:
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90 if (bt && H5AC_unprotect (f, H5AC_BT, addr, bt)<0) {
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91 HRETURN_ERROR (H5E_BTREE, H5E_PROTECT, FAIL);
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92 }
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93 FUNC_LEAVE (ret_value);
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94 }
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</pre></code>
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<p>For lack of a better way to handle errors during error cleanup,
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I just call the <code>HRETURN_ERROR</code> macro even though it
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will make the error stack not quite right. I also use short
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circuiting boolean operators instead of nested <code>if</code>
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statements since that's standard C practice.
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<center><h1>Code Review 2</h1></center>
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<p>The following code is an API function from the H5F package...
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<p><code><pre>
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1 /*--------------------------------------------------------------------------
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2 NAME
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3 H5Fflush
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4
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5 PURPOSE
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6 Flush all cached data to disk and optionally invalidates all cached
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7 data.
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8
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9 USAGE
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10 herr_t H5Fflush(fid, invalidate)
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11 hid_t fid; IN: File ID of file to close.
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12 hbool_t invalidate; IN: Invalidate all of the cache?
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13
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14 ERRORS
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15 ARGS BADTYPE Not a file atom.
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16 ATOM BADATOM Can't get file struct.
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17 CACHE CANTFLUSH Flush failed.
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18
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19 RETURNS
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20 SUCCEED/FAIL
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21
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22 DESCRIPTION
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23 This function flushes all cached data to disk and, if INVALIDATE
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24 is non-zero, removes cached objects from the cache so they must be
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25 re-read from the file on the next access to the object.
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26
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27 MODIFICATIONS:
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28 --------------------------------------------------------------------------*/
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</pre></code>
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<p>An API prologue is used for each API function instead of my
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normal function prologue. I use the prologue from Code Review 1
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for non-API functions because it's more suited to C programmers,
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it requires less work to keep it synchronized with the code, and
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I have better editing tools for it.
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<p><code><pre>
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29 herr_t
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30 H5Fflush (hid_t fid, hbool_t invalidate)
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31 {
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32 H5F_t *file = NULL;
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33
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34 FUNC_ENTER (H5Fflush, H5F_init_interface, FAIL);
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35 H5ECLEAR;
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</pre></code>
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<p>API functions are never called internally, therefore I always
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clear the error stack before doing anything.
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<p><code><pre>
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36
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37 /* check arguments */
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38 if (H5_FILE!=H5Aatom_group (fid)) {
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39 HRETURN_ERROR (H5E_ARGS, H5E_BADTYPE, FAIL); /*not a file atom*/
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40 }
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41 if (NULL==(file=H5Aatom_object (fid))) {
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42 HRETURN_ERROR (H5E_ATOM, H5E_BADATOM, FAIL); /*can't get file struct*/
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43 }
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</pre></code>
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<p>If something is wrong with the arguments then we raise an
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error. We never <code>assert</code> arguments at this level.
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We also convert atoms to pointers since atoms are really just a
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pointer-hiding mechanism. Functions that can be called
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internally always have pointer arguments instead of atoms
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because (1) then they don't have to always convert atoms to
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pointers, and (2) the various pointer data types provide more
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documentation and type checking than just an <code>hid_t</code>
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type.
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<p><code><pre>
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44
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45 /* do work */
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46 if (H5F_flush (file, invalidate)<0) {
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47 HRETURN_ERROR (H5E_CACHE, H5E_CANTFLUSH, FAIL); /*flush failed*/
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48 }
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</pre></code>
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<p>An internal version of the function does the real work. That
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internal version calls <code>assert</code> to check/document
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it's arguments and can be called from other library functions.
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<p><code><pre>
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49
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50 FUNC_LEAVE (SUCCEED);
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51 }
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</pre></code>
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<hr>
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<address><a href="mailto:matzke@llnl.gov">Robb Matzke</a></address>
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<!-- Created: Sat Nov 8 17:09:33 EST 1997 -->
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<!-- hhmts start -->
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Last modified: Mon Nov 10 15:33:33 EST 1997
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<!-- hhmts end -->
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</body>
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</html>
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