gdbm documentation

--- gdbm-cvs1.39/gdbm.c	2006-09-19 17:19:24.000000000 +0200
+++ gdbm/gdbm.c	2006-09-19 19:42:20.000000000 +0200
@@ -6,6 +6,8 @@
   $Date: 2006/09/02 14:41:01 $
   modified at: Mon Jan 24 15:59:52 JST 1994
 
+  Documentation by Peter Adolphs < futzilogik at users dot sourceforge dot net >
+
 ************************************************/
 
 #include "ruby.h"
@@ -14,6 +16,62 @@
 #include <fcntl.h>
 #include <errno.h>
 
+/*
+ * Document-class: GDBM
+ *
+ * == Summary
+ *
+ * Ruby extension for GNU dbm (gdbm) -- a simple database engine for storing
+ * key-value pairs on disk.
+ *
+ * == Description
+ *
+ * GNU dbm is a library for simple databases. A database is a file that stores
+ * key-value pairs. Gdbm allows the user to store, retrieve, and delete data by
+ * key. It furthermore allows a non-sorted traversal of all key-value pairs.
+ * A gdbm database thus provides the same functionality as a hash. As
+ * with objects of the Hash class, elements can be accessed with <tt>[]</tt>.
+ * Furthermore, GDBM mixes in the Enumerable module, thus providing convenient
+ * methods such as #find, #collect, #map, etc.
+ *
+ * A process is allowed to open several different databases at the same time.
+ * A process can open a database as a "reader" or a "writer". Whereas a reader
+ * has only read-access to the database, a writer has read- and write-access.
+ * A database can be accessed either by any number of readers or by exactly one
+ * writer at the same time.
+ *
+ * == Examples
+ *
+ * 1. Opening/creating a database, and filling it with some entries:
+ *
+ *      require 'gdbm'
+ *      
+ *      gdbm = GDBM.new("fruitstore.db")
+ *      gdbm["ananas"]    = "3"
+ *      gdbm["banana"]    = "8"
+ *      gdbm["cranberry"] = "4909"
+ *      gdbm.close
+ *
+ * 2. Reading out a database:
+ *
+ *      require 'gdbm'
+ *      
+ *      gdbm = GDBM.new("fruitstore.db")
+ *      gdbm.each_pair do |key, value|
+ *        print "#{key}: #{value}\n"
+ *      end
+ *      gdbm.close
+ *
+ *    produces
+ *
+ *      banana: 8
+ *      ananas: 3
+ *      cranberry: 4909
+ *
+ * == Links
+ *
+ * * http://www.gnu.org/software/gdbm/
+ */
 static VALUE rb_cGDBM, rb_eGDBMError, rb_eGDBMFatalError;
 
 #define RUBY_GDBM_RW_BIT 0x20000000
@@ -52,11 +110,17 @@
 free_dbm(struct dbmdata *dbmp)
 {
     if (dbmp) {
-	if (dbmp->di_dbm) gdbm_close(dbmp->di_dbm);
-	free(dbmp);
+        if (dbmp->di_dbm) gdbm_close(dbmp->di_dbm);
+        free(dbmp);
     }
 }
 
+/*
+ * call-seq:
+ *     gdbm.close -> nil
+ *
+ * Closes the associated database file.
+ */
 static VALUE
 fgdbm_close(VALUE obj)
 {
@@ -69,6 +133,12 @@
     return Qnil;
 }
 
+/*
+ * call-seq:
+ *     gdbm.closed?  -> true or false
+ *
+ * Returns true if the associated database file has been closed.
+ */
 static VALUE
 fgdbm_closed(VALUE obj)
 {
@@ -76,9 +146,9 @@
 
     Data_Get_Struct(obj, struct dbmdata, dbmp);
     if (dbmp == 0)
-	return Qtrue;
+        return Qtrue;
     if (dbmp->di_dbm == 0)
-	return Qtrue;
+        return Qtrue;
 
     return Qfalse;
 }
@@ -89,6 +159,29 @@
     return Data_Wrap_Struct(klass, 0, free_dbm, 0);
 }
 
+/*
+ * call-seq:
+ *      GDBM.new(filename, mode = 0666, flags = nil)
+ *
+ * Creates a new GDBM instance by opening a gdbm file named _filename_.
+ * If the file does not exist, a new file with file mode _mode_ will be
+ * created. _flags_ may be one of the following:
+ * * *READER*  - open as a reader
+ * * *WRITER*  - open as a writer
+ * * *WRCREAT* - open as a writer; if the database does not exist, create a new one
+ * * *NEWDB*   - open as a writer; overwrite any existing databases
+ *
+ * The values *WRITER*, *WRCREAT* and *NEWDB* may be combined with the following
+ * values by bitwise or:
+ * * *SYNC*    - cause all database operations to be synchronized to the disk
+ * * *NOLOCK*  - do not lock the database file
+ *
+ * If no _flags_ are specified, the GDBM object will try to open the database
+ * file as a writer and will create it if it does not already exist
+ * (cf. flag <tt>WRCREAT</tt>). If this fails (for instance, if another process
+ * has already opened the database as a reader), it will try to open the
+ * database file as a reader (cf. flag <tt>READER</tt>).
+ */
 static VALUE
 fgdbm_initialize(int argc, VALUE *argv, VALUE obj)
 {
@@ -98,13 +191,13 @@
     int mode, flags = 0;
 
     if (rb_scan_args(argc, argv, "12", &file, &vmode, &vflags) == 1) {
-	mode = 0666;		/* default value */
+        mode = 0666;            /* default value */
     }
     else if (NIL_P(vmode)) {
-	mode = -1;		/* return nil if DB not exist */
+        mode = -1;              /* return nil if DB does not exist */
     }
     else {
-	mode = NUM2INT(vmode);
+        mode = NUM2INT(vmode);
     }
 
     if (!NIL_P(vflags))
@@ -114,8 +207,8 @@
 
     if (flags & RUBY_GDBM_RW_BIT) {
         flags &= ~RUBY_GDBM_RW_BIT;
-	dbm = gdbm_open(RSTRING_PTR(file), MY_BLOCK_SIZE, 
-			flags, mode, MY_FATAL_FUNC);
+        dbm = gdbm_open(RSTRING_PTR(file), MY_BLOCK_SIZE, 
+                        flags, mode, MY_FATAL_FUNC);
     }
     else {
         dbm = 0;
@@ -131,14 +224,14 @@
     }
 
     if (!dbm) {
-	if (mode == -1) return Qnil;
+        if (mode == -1) return Qnil;
 
-	if (gdbm_errno == GDBM_FILE_OPEN_ERROR ||
-	    gdbm_errno == GDBM_CANT_BE_READER ||
-	    gdbm_errno == GDBM_CANT_BE_WRITER)
-	    rb_sys_fail(RSTRING_PTR(file));
-	else
-	    rb_raise(rb_eGDBMError, "%s", gdbm_strerror(gdbm_errno));
+        if (gdbm_errno == GDBM_FILE_OPEN_ERROR ||
+            gdbm_errno == GDBM_CANT_BE_READER ||
+            gdbm_errno == GDBM_CANT_BE_WRITER)
+            rb_sys_fail(RSTRING_PTR(file));
+        else
+            rb_raise(rb_eGDBMError, "%s", gdbm_strerror(gdbm_errno));
     }
 
     dbmp = ALLOC(struct dbmdata);
@@ -150,13 +243,32 @@
     return obj;
 }
 
+/*
+ * call-seq:
+ *      GDBM.open(filename, mode = 0666, flags = nil)
+ *      GDBM.open(filename, mode = 0666, flags = nil) { |gdbm| ... }
+ *
+ * If called without a block, this is synonymous to GDBM::new.
+ * If a block is given, the new GDBM instance will be passed to the block
+ * as a parameter, and the corresponding database file will be closed
+ * after the execution of the block code has been finished.
+ *
+ * Example for an open call with a block:
+ *
+ *   require 'gdbm'
+ *   GDBM.open("fruitstore.db") do |gdbm|
+ *     gdbm.each_pair do |key, value|
+ *       print "#{key}: #{value}\n"
+ *     end
+ *   end
+ */
 static VALUE
 fgdbm_s_open(int argc, VALUE *argv, VALUE klass)
 {
     VALUE obj = Data_Wrap_Struct(klass, 0, free_dbm, 0);
 
     if (NIL_P(fgdbm_initialize(argc, argv, obj))) {
-	return Qnil;
+        return Qnil;
     }
 
     if (rb_block_given_p()) {
@@ -244,19 +356,32 @@
 
     valstr = rb_gdbm_fetch3(obj, keystr);
     if (NIL_P(valstr)) {
-	if (ifnone == Qnil && rb_block_given_p())
-	    return rb_yield(keystr);
-	return ifnone;
+        if (ifnone == Qnil && rb_block_given_p())
+            return rb_yield(keystr);
+        return ifnone;
     }
     return valstr;
 }
 
+/*
+ * call-seq:
+ *      gdbm[key] -> value
+ *
+ * Retrieves the _value_ corresponding to _key_.
+ */
 static VALUE
 fgdbm_aref(VALUE obj, VALUE keystr)
 {
     return rb_gdbm_fetch3(obj, keystr);
 }
 
+/*
+ * call-seq:
+ *      gdbm.fetch(key [, default]) -> value
+ *
+ * Retrieves the _value_ corresponding to _key_. If there is no value
+ * associated with _key_, _default_ will be returned instead.
+ */
 static VALUE
 fgdbm_fetch_m(int argc, VALUE *argv, VALUE obj)
 {
@@ -265,11 +390,18 @@
     rb_scan_args(argc, argv, "11", &keystr, &ifnone);
     valstr = fgdbm_fetch(obj, keystr, ifnone);
     if (argc == 1 && !rb_block_given_p() && NIL_P(valstr))
-	rb_raise(rb_eIndexError, "key not found");
+        rb_raise(rb_eIndexError, "key not found");
 
     return valstr;
 }
 
+/*
+ * call-seq:
+ *      gdbm.index(value) -> key
+ *
+ * Returns the _key_ for a given _value_. If several keys may map to the
+ * same value, the key that is found first will be returned.
+ */
 static VALUE
 fgdbm_index(VALUE obj, VALUE valstr)
 {
@@ -282,17 +414,24 @@
     for (keystr = rb_gdbm_firstkey(dbm); RTEST(keystr);
          keystr = rb_gdbm_nextkey(dbm, keystr)) {
 
-	valstr2 = rb_gdbm_fetch2(dbm, keystr);
+        valstr2 = rb_gdbm_fetch2(dbm, keystr);
         if (!NIL_P(valstr2) &&
             RSTRING_LEN(valstr) == RSTRING_LEN(valstr2) &&
             memcmp(RSTRING_PTR(valstr), RSTRING_PTR(valstr2),
                    RSTRING_LEN(valstr)) == 0) {
-	    return keystr;
+            return keystr;
         }
     }
     return Qnil;
 }
 
+/*
+ * call-seq:
+ *      gdbm.select { |value| block } -> array
+ *
+ * Returns a new array of all values of the database for which _block_
+ * evaluates to true.
+ */
 static VALUE
 fgdbm_select(VALUE obj)
 {
@@ -303,19 +442,25 @@
 
     GetDBM2(obj, dbmp, dbm);
     for (keystr = rb_gdbm_firstkey(dbm); RTEST(keystr);
-	 keystr = rb_gdbm_nextkey(dbm, keystr)) {
-	VALUE assoc = rb_assoc_new(keystr, rb_gdbm_fetch2(dbm, keystr));
-	VALUE v = rb_yield(assoc);
-
-	if (RTEST(v)) {
-	    rb_ary_push(new, assoc);
-	}
-	GetDBM2(obj, dbmp, dbm);
+         keystr = rb_gdbm_nextkey(dbm, keystr)) {
+        VALUE assoc = rb_assoc_new(keystr, rb_gdbm_fetch2(dbm, keystr));
+        VALUE v = rb_yield(assoc);
+
+        if (RTEST(v)) {
+            rb_ary_push(new, assoc);
+        }
+        GetDBM2(obj, dbmp, dbm);
     }
 
     return new;
 }
 
+/*
+ * call-seq:
+ *      gdbm.values_at(key, ...) -> array
+ *
+ * Returns an array of the values associated with each specified _key_.
+ */
 static VALUE
 fgdbm_values_at(int argc, VALUE *argv, VALUE obj)
 {
@@ -350,19 +495,26 @@
 
     GetDBM2(obj, dbmp, dbm);
     if (!gdbm_exists(dbm, key)) {
-	return Qnil;
+        return Qnil;
     }
 
     if (gdbm_delete(dbm, key)) {
-	dbmp->di_size = -1;
-	rb_raise(rb_eGDBMError, "%s", gdbm_strerror(gdbm_errno));
+        dbmp->di_size = -1;
+        rb_raise(rb_eGDBMError, "%s", gdbm_strerror(gdbm_errno));
     }
     else if (dbmp->di_size >= 0) {
-	dbmp->di_size--;
+        dbmp->di_size--;
     }
     return obj;
 }
 
+/*
+ * call-seq:
+ *      gdbm.delete(key) -> value or nil
+ *
+ * Removes the key-value-pair with the specified _key_ from this database and
+ * returns the corresponding _value_. Returns nil if the database is empty.
+ */
 static VALUE
 fgdbm_delete(VALUE obj, VALUE keystr)
 {
@@ -373,6 +525,13 @@
     return valstr;
 }
 
+/*
+ * call-seq:
+ *      gdbm.shift -> (key, value) or nil
+ *
+ * Removes a key-value-pair from this database and returns it as a 
+ * two-item array [ _key_, _value_ ]. Returns nil if the database is empty.
+ */
 static VALUE
 fgdbm_shift(VALUE obj)
 {
@@ -390,6 +549,13 @@
     return rb_assoc_new(keystr, valstr);
 }
 
+/*
+ * call-seq:
+ *      gdbm.delete_if { |key, value| block } -> gdbm
+ *      gdbm.reject! { |key, value| block } -> gdbm
+ *
+ * Deletes every key-value pair from _gdbm_ for which _block_ evaluates to true.
+ */
 static VALUE
 fgdbm_delete_if(VALUE obj)
 {
@@ -407,11 +573,11 @@
     for (keystr = rb_gdbm_firstkey(dbm); RTEST(keystr);
          keystr = rb_gdbm_nextkey(dbm, keystr)) {
 
-	valstr = rb_gdbm_fetch2(dbm, keystr);
+        valstr = rb_gdbm_fetch2(dbm, keystr);
         ret = rb_protect(rb_yield, rb_assoc_new(keystr, valstr), &status);
         if (status != 0) break;
-	if (RTEST(ret)) rb_ary_push(ary, keystr);
-	GetDBM2(obj, dbmp, dbm);
+        if (RTEST(ret)) rb_ary_push(ary, keystr);
+        GetDBM2(obj, dbmp, dbm);
     }
 
     for (i = 0; i < RARRAY_LEN(ary); i++)
@@ -422,6 +588,12 @@
     return obj;
 }
 
+/*
+ * call-seq:
+ *      gdbm.clear -> gdbm
+ *
+ * Removes all the key-value pairs within _gdbm_.
+ */
 static VALUE
 fgdbm_clear(VALUE obj)
 {
@@ -435,11 +607,11 @@
 
 #if 0
     while (key = gdbm_firstkey(dbm), key.dptr) {
-	if (gdbm_delete(dbm, key)) {
-	    free(key.dptr);
-	    rb_raise(rb_eGDBMError, "%s", gdbm_strerror(gdbm_errno));
-	}
-	free(key.dptr); 
+        if (gdbm_delete(dbm, key)) {
+            free(key.dptr);
+            rb_raise(rb_eGDBMError, "%s", gdbm_strerror(gdbm_errno));
+        }
+        free(key.dptr); 
     }
 #else
     while (key = gdbm_firstkey(dbm), key.dptr) {
@@ -459,6 +631,13 @@
     return obj;
 }
 
+/*
+ * call-seq:
+ *     gdbm.invert  -> hash
+ *
+ * Returns a hash created by using _gdbm_'s values as keys, and the keys
+ * as values.
+ */
 static VALUE
 fgdbm_invert(VALUE obj)
 {
@@ -470,13 +649,20 @@
     GetDBM2(obj, dbmp, dbm);
     for (keystr = rb_gdbm_firstkey(dbm); RTEST(keystr);
          keystr = rb_gdbm_nextkey(dbm, keystr)) {
-	valstr = rb_gdbm_fetch2(dbm, keystr);
+        valstr = rb_gdbm_fetch2(dbm, keystr);
 
-	rb_hash_aset(hash, valstr, keystr);
+        rb_hash_aset(hash, valstr, keystr);
     }
     return hash;
 }
 
+/*
+ * call-seq:
+ *      gdbm[key]= value -> value
+ *      gdbm.store(key, value) -> value
+ *
+ * Associates the value _value_ with the specified _key_.
+ */
 static VALUE
 fgdbm_store(VALUE obj, VALUE keystr, VALUE valstr)
 {
@@ -497,8 +683,8 @@
     GetDBM2(obj, dbmp, dbm);
     dbmp->di_size = -1;
     if (gdbm_store(dbm, key, val, GDBM_REPLACE)) {
-	if (errno == EPERM) rb_sys_fail(0);
-	rb_raise(rb_eGDBMError, "%s", gdbm_strerror(gdbm_errno));
+        if (errno == EPERM) rb_sys_fail(0);
+        rb_raise(rb_eGDBMError, "%s", gdbm_strerror(gdbm_errno));
     }
 
     return valstr;
@@ -509,12 +695,20 @@
 {
     Check_Type(pair, T_ARRAY);
     if (RARRAY_LEN(pair) < 2) {
-	rb_raise(rb_eArgError, "pair must be [key, value]");
+        rb_raise(rb_eArgError, "pair must be [key, value]");
     }
     fgdbm_store(dbm, RARRAY_PTR(pair)[0], RARRAY_PTR(pair)[1]);
     return Qnil;
 }
 
+/*
+ * call-seq:
+ *     gdbm.update(other) -> gdbm
+ *
+ * Adds the key-value pairs of _other_ to _gdbm_, overwriting entries with
+ * duplicate keys with those from _other_. _other_ must have an each_pair
+ * method.
+ */
 static VALUE
 fgdbm_update(VALUE obj, VALUE other)
 {
@@ -522,6 +716,13 @@
     return obj;
 }
 
+/*
+ * call-seq:
+ *     gdbm.replace(other) -> gdbm
+ *
+ * Replaces the content of _gdbm_ with the key-value pairs of _other_.
+ * _other_ must have an each_pair method.
+ */
 static VALUE
 fgdbm_replace(VALUE obj, VALUE other)
 {
@@ -530,6 +731,13 @@
     return obj;
 }
 
+/*
+ * call-seq:
+ *      gdbm.length -> fixnum
+ *      gdbm.size -> fixnum
+ *
+ * Returns the number of key-value pairs in this database.
+ */
 static VALUE
 fgdbm_length(VALUE obj)
 {
@@ -544,13 +752,19 @@
     for (key = gdbm_firstkey(dbm); key.dptr; key = nextkey) {
         nextkey = gdbm_nextkey(dbm, key);
         free(key.dptr);
-	i++;
+        i++;
     }
     dbmp->di_size = i;
 
     return INT2FIX(i);
 }
 
+/*
+ * call-seq:
+ *      gdbm.empty? -> true or false
+ *
+ * Returns true if the database is empty.
+ */
 static VALUE
 fgdbm_empty_p(VALUE obj)
 {
@@ -560,13 +774,13 @@
 
     GetDBM(obj, dbmp);
     if (dbmp->di_size < 0) {
-	dbm = dbmp->di_dbm;
+        dbm = dbmp->di_dbm;
 
-	key = gdbm_firstkey(dbm);
+        key = gdbm_firstkey(dbm);
         if (key.dptr) {
             free(key.dptr);
             return Qfalse;
-	}
+        }
         return Qtrue;
     }
 
@@ -574,6 +788,13 @@
     return Qfalse;
 }
 
+/*
+ * call-seq:
+ *      gdbm.each_value { |value| block } -> gdbm
+ *
+ * Executes _block_ for each key in the database, passing the corresponding
+ * _value_ as a parameter.
+ */
 static VALUE
 fgdbm_each_value(VALUE obj)
 {
@@ -586,11 +807,18 @@
          keystr = rb_gdbm_nextkey(dbm, keystr)) {
 
         rb_yield(rb_gdbm_fetch2(dbm, keystr));
-	GetDBM2(obj, dbmp, dbm);
+        GetDBM2(obj, dbmp, dbm);
     }
     return obj;
 }
 
+/*
+ * call-seq:
+ *      gdbm.each_key { |key| block } -> gdbm
+ *
+ * Executes _block_ for each key in the database, passing the
+ * _key_ as a parameter.
+ */
 static VALUE
 fgdbm_each_key(VALUE obj)
 {
@@ -603,11 +831,18 @@
          keystr = rb_gdbm_nextkey(dbm, keystr)) {
 
         rb_yield(keystr);
-	GetDBM2(obj, dbmp, dbm);
+        GetDBM2(obj, dbmp, dbm);
     }
     return obj;
 }
 
+/*
+ * call-seq:
+ *      gdbm.each_pair { |key, value| block } -> gdbm
+ *
+ * Executes _block_ for each key in the database, passing the _key_ and the
+ * correspoding _value_ as a parameter.
+ */
 static VALUE
 fgdbm_each_pair(VALUE obj)
 {
@@ -620,12 +855,18 @@
          keystr = rb_gdbm_nextkey(dbm, keystr)) {
 
         rb_yield(rb_assoc_new(keystr, rb_gdbm_fetch2(dbm, keystr)));
-	GetDBM2(obj, dbmp, dbm);
+        GetDBM2(obj, dbmp, dbm);
     }
 
     return obj;
 }
 
+/*
+ * call-seq:
+ *      gdbm.keys -> array
+ *
+ * Returns an array of all keys of this database.
+ */
 static VALUE
 fgdbm_keys(VALUE obj)
 {
@@ -644,6 +885,12 @@
     return ary;
 }
 
+/*
+ * call-seq:
+ *      gdbm.values -> array
+ *
+ * Returns an array of all values of this database.
+ */
 static VALUE
 fgdbm_values(VALUE obj)
 {
@@ -656,14 +903,22 @@
     ary = rb_ary_new();
     for (key = gdbm_firstkey(dbm); key.dptr; key = nextkey) {
         nextkey = gdbm_nextkey(dbm, key);
-	valstr = rb_gdbm_fetch(dbm, key);
+        valstr = rb_gdbm_fetch(dbm, key);
         free(key.dptr);
-	rb_ary_push(ary, valstr);
+        rb_ary_push(ary, valstr);
     }
 
     return ary;
 }
 
+/*
+ * call-seq:
+ *      gdbm.has_key?(k) -> true or false
+ *      gdbm.key?(k) -> true or false
+ *
+ * Returns true if the given key _k_ exists within the database.
+ * Returns false otherwise.
+ */
 static VALUE
 fgdbm_has_key(VALUE obj, VALUE keystr)
 {
@@ -681,6 +936,14 @@
     return Qfalse;
 }
 
+/*
+ * call-seq:
+ *      gdbm.has_value?(v) -> true or false
+ *      gdbm.value?(v) -> true or false
+ *
+ * Returns true if the given value _v_ exists within the database.
+ * Returns false otherwise.
+ */
 static VALUE
 fgdbm_has_value(VALUE obj, VALUE valstr)
 {
@@ -693,18 +956,24 @@
     for (keystr = rb_gdbm_firstkey(dbm); RTEST(keystr);
          keystr = rb_gdbm_nextkey(dbm, keystr)) {
 
-	valstr2 = rb_gdbm_fetch2(dbm, keystr);
+        valstr2 = rb_gdbm_fetch2(dbm, keystr);
 
         if (!NIL_P(valstr2) &&
             RSTRING_LEN(valstr) == RSTRING_LEN(valstr2) &&
             memcmp(RSTRING_PTR(valstr), RSTRING_PTR(valstr2),
                    RSTRING_LEN(valstr)) == 0) {
-	    return Qtrue;
+            return Qtrue;
         }
     }
     return Qfalse;
 }
 
+/*
+ * call-seq:
+ *     gdbm.to_a -> array
+ *
+ * Returns an array of all key-value pairs contained in the database.
+ */
 static VALUE
 fgdbm_to_a(VALUE obj)
 {
@@ -723,6 +992,14 @@
     return ary;
 }
 
+/*
+ * call-seq:
+ *     gdbm.reorganize -> gdbm
+ *
+ * Reorganizes the database file. This operation removes reserved space of
+ * elements that have already been deleted. It is only useful after a lot of
+ * deletions in the database.
+ */
 static VALUE
 fgdbm_reorganize(VALUE obj)
 {
@@ -735,6 +1012,16 @@
     return obj;
 }
 
+/*
+ * call-seq:
+ *     gdbm.sync -> gdbm
+ *
+ * Unless the _gdbm_ object has been opened with the *SYNC* flag, it is not
+ * guarenteed that database modification operations are immediately applied to
+ * the database file. This method ensures that all recent modifications
+ * to the database are written to the file. Blocks until all writing operations
+ * to the disk have been finished.
+ */
 static VALUE
 fgdbm_sync(VALUE obj)
 {
@@ -747,6 +1034,12 @@
     return obj;
 }
 
+/*
+ * call-seq:
+ *     gdbm.cachesize = size -> size
+ *
+ * Sets the size of the internal bucket cache to _size_.
+ */
 static VALUE
 fgdbm_set_cachesize(VALUE obj, VALUE val)
 {
@@ -757,11 +1050,21 @@
     GetDBM2(obj, dbmp, dbm);
     optval = FIX2INT(val);
     if (gdbm_setopt(dbm, GDBM_CACHESIZE, &optval, sizeof(optval)) == -1) {
-	rb_raise(rb_eGDBMError, "%s", gdbm_strerror(gdbm_errno));
+        rb_raise(rb_eGDBMError, "%s", gdbm_strerror(gdbm_errno));
     }
     return val;
 }
 
+/*
+ * call-seq:
+ *     gdbm.fastmode = boolean -> boolean
+ *
+ * Turns the database's fast mode on or off. If fast mode is turned on, gdbm
+ * does not wait for writes to be flushed to the disk before continuing.
+ *
+ * This option is obsolete for gdbm >= 1.8 since fast mode is turned on by
+ * default. See also: #syncmode=
+ */
 static VALUE
 fgdbm_set_fastmode(VALUE obj, VALUE val)
 {
@@ -775,11 +1078,24 @@
         optval = 1;
 
     if (gdbm_setopt(dbm, GDBM_FASTMODE, &optval, sizeof(optval)) == -1) {
-	rb_raise(rb_eGDBMError, "%s", gdbm_strerror(gdbm_errno));
+        rb_raise(rb_eGDBMError, "%s", gdbm_strerror(gdbm_errno));
     }
     return val;
 }
 
+/*
+ * call-seq:
+ *     gdbm.syncmode = boolean -> boolean
+ *
+ * Turns the database's synchronization mode on or off. If the synchronization
+ * mode is turned on, the database's in-memory state will be synchronized to
+ * disk after every database modification operation. If the synchronization
+ * mode is turned off, GDBM does not wait for writes to be flushed to the disk
+ * before continuing.
+ *
+ * This option is only available for gdbm >= 1.8 where syncmode is turned off
+ * by default. See also: #fastmode=
+ */
 static VALUE
 fgdbm_set_syncmode(VALUE obj, VALUE val)
 {
@@ -797,12 +1113,18 @@
         optval = 1;
 
     if (gdbm_setopt(dbm, GDBM_FASTMODE, &optval, sizeof(optval)) == -1) {
-	rb_raise(rb_eGDBMError, "%s", gdbm_strerror(gdbm_errno));
+        rb_raise(rb_eGDBMError, "%s", gdbm_strerror(gdbm_errno));
     }
     return val;
 #endif
 }
 
+/*
+ * call-seq:
+ *     gdbm.to_hash -> hash
+ *
+ * Returns a hash of all key-value pairs contained in the database.
+ */
 static VALUE
 fgdbm_to_hash(VALUE obj)
 {
@@ -821,6 +1143,13 @@
     return hash;
 }
 
+/*
+ * call-seq:
+ *      gdbm.reject { |key, value| block } -> hash
+ *
+ * Returns a hash copy of _gdbm_ where all key-value pairs from _gdbm_ for
+ * which _block_ evaluates to true are removed. See also: #delete_if
+ */
 static VALUE
 fgdbm_reject(VALUE obj)
 {
@@ -863,15 +1192,15 @@
     rb_define_method(rb_cGDBM, "reject!", fgdbm_delete_if, 0);
     rb_define_method(rb_cGDBM, "reject", fgdbm_reject, 0);
     rb_define_method(rb_cGDBM, "clear", fgdbm_clear, 0);
-    rb_define_method(rb_cGDBM,"invert", fgdbm_invert, 0);
-    rb_define_method(rb_cGDBM,"update", fgdbm_update, 1);
-    rb_define_method(rb_cGDBM,"replace", fgdbm_replace, 1);
-    rb_define_method(rb_cGDBM,"reorganize", fgdbm_reorganize, 0);
-    rb_define_method(rb_cGDBM,"sync", fgdbm_sync, 0);
-    /* rb_define_method(rb_cGDBM,"setopt", fgdbm_setopt, 2); */
-    rb_define_method(rb_cGDBM,"cachesize=", fgdbm_set_cachesize, 1);
-    rb_define_method(rb_cGDBM,"fastmode=", fgdbm_set_fastmode, 1);
-    rb_define_method(rb_cGDBM,"syncmode=", fgdbm_set_syncmode, 1);
+    rb_define_method(rb_cGDBM, "invert", fgdbm_invert, 0);
+    rb_define_method(rb_cGDBM, "update", fgdbm_update, 1);
+    rb_define_method(rb_cGDBM, "replace", fgdbm_replace, 1);
+    rb_define_method(rb_cGDBM, "reorganize", fgdbm_reorganize, 0);
+    rb_define_method(rb_cGDBM, "sync", fgdbm_sync, 0);
+    /* rb_define_method(rb_cGDBM, "setopt", fgdbm_setopt, 2); */
+    rb_define_method(rb_cGDBM, "cachesize=", fgdbm_set_cachesize, 1);
+    rb_define_method(rb_cGDBM, "fastmode=", fgdbm_set_fastmode, 1);
+    rb_define_method(rb_cGDBM, "syncmode=", fgdbm_set_syncmode, 1);
 
     rb_define_method(rb_cGDBM, "include?", fgdbm_has_key, 1);
     rb_define_method(rb_cGDBM, "has_key?", fgdbm_has_key, 1);
@@ -883,22 +1212,29 @@
     rb_define_method(rb_cGDBM, "to_a", fgdbm_to_a, 0);
     rb_define_method(rb_cGDBM, "to_hash", fgdbm_to_hash, 0);
 
-    /* flags for gdbm_open() */
+    /* flag for #new and #open: open database as a reader */
     rb_define_const(rb_cGDBM, "READER",  INT2FIX(GDBM_READER|RUBY_GDBM_RW_BIT));
+    /* flag for #new and #open: open database as a writer */
     rb_define_const(rb_cGDBM, "WRITER",  INT2FIX(GDBM_WRITER|RUBY_GDBM_RW_BIT));
+    /* flag for #new and #open: open database as a writer; if the database does not exist, create a new one */
     rb_define_const(rb_cGDBM, "WRCREAT", INT2FIX(GDBM_WRCREAT|RUBY_GDBM_RW_BIT));
+    /* flag for #new and #open: open database as a writer; overwrite any existing databases  */
     rb_define_const(rb_cGDBM, "NEWDB",   INT2FIX(GDBM_NEWDB|RUBY_GDBM_RW_BIT));
 
+    /* flag for #new and #open. this flag is obsolete for gdbm >= 1.8 */
     rb_define_const(rb_cGDBM, "FAST", INT2FIX(GDBM_FAST));
     /* this flag is obsolete in gdbm 1.8.
        On gdbm 1.8, fast mode is default behavior. */
 
     /* gdbm version 1.8 specific */
 #if defined(GDBM_SYNC)
+    /* flag for #new and #open. only for gdbm >= 1.8 */
     rb_define_const(rb_cGDBM, "SYNC",    INT2FIX(GDBM_SYNC));
 #endif
 #if defined(GDBM_NOLOCK)
+    /* flag for #new and #open */
     rb_define_const(rb_cGDBM, "NOLOCK",  INT2FIX(GDBM_NOLOCK));
 #endif
+    /* version of the gdbm library*/
     rb_define_const(rb_cGDBM, "VERSION",  rb_str_new2(gdbm_version));
 }