diff options
Diffstat (limited to 'manual')
| -rw-r--r-- | manual/search.texi | 72 |
1 files changed, 72 insertions, 0 deletions
diff --git a/manual/search.texi b/manual/search.texi index a714ba7812..509a54313a 100644 --- a/manual/search.texi +++ b/manual/search.texi @@ -72,6 +72,7 @@ two functions can be found in @file{search.h}. @comment search.h @comment SVID @deftypefun {void *} lfind (const void *@var{key}, const void *@var{base}, size_t *@var{nmemb}, size_t @var{size}, comparison_fn_t @var{compar}) +@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} The @code{lfind} function searches in the array with @code{*@var{nmemb}} elements of @var{size} bytes pointed to by @var{base} for an element which matches the one pointed to by @var{key}. The function pointed to @@ -90,6 +91,21 @@ searching. @comment search.h @comment SVID @deftypefun {void *} lsearch (const void *@var{key}, void *@var{base}, size_t *@var{nmemb}, size_t @var{size}, comparison_fn_t @var{compar}) +@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} +@c A signal handler that interrupted an insertion and performed an +@c insertion itself would leave the array in a corrupt state (e.g. one +@c new element initialized twice, with parts of both initializations +@c prevailing, and another uninitialized element), but this is just a +@c special case of races on user-controlled objects, that have to be +@c avoided by users. + +@c In case of cancellation, we know the array won't be left in a corrupt +@c state; the new element is initialized before the element count is +@c incremented, and the compiler can't reorder these operations because +@c it can't know that they don't alias. So, we'll either cancel after +@c the increment and the initialization are both complete, or the +@c increment won't have taken place, and so how far the initialization +@c got doesn't matter. The @code{lsearch} function is similar to the @code{lfind} function. It searches the given array for an element and returns it if found. The difference is that if no matching element is found the @code{lsearch} @@ -113,6 +129,7 @@ the header file @file{stdlib.h}. @comment stdlib.h @comment ISO @deftypefun {void *} bsearch (const void *@var{key}, const void *@var{array}, size_t @var{count}, size_t @var{size}, comparison_fn_t @var{compare}) +@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} The @code{bsearch} function searches the sorted array @var{array} for an object that is equivalent to @var{key}. The array contains @var{count} elements, each of which is of size @var{size} bytes. @@ -146,6 +163,7 @@ To sort an array using an arbitrary comparison function, use the @comment stdlib.h @comment ISO @deftypefun void qsort (void *@var{array}, size_t @var{count}, size_t @var{size}, comparison_fn_t @var{compare}) +@safety{@prelim{}@mtsafe{}@assafe{}@acunsafe{@acucorrupt{}}} The @var{qsort} function sorts the array @var{array}. The array contains @var{count} elements, each of which is of size @var{size}. @@ -256,6 +274,9 @@ The following functions are declared in the header file @file{search.h}. @comment search.h @comment SVID @deftypefun int hcreate (size_t @var{nel}) +@safety{@prelim{}@mtunsafe{@mtasurace{:hsearch}}@asunsafe{@ascuheap{}}@acunsafe{@acucorrupt{} @acsmem{}}} +@c hcreate @mtasurace:hsearch @ascuheap @acucorrupt @acsmem +@c hcreate_r dup @mtsrace:htab @ascuheap @acucorrupt @acsmem The @code{hcreate} function creates a hashing table which can contain at least @var{nel} elements. There is no possibility to grow this table so it is necessary to choose the value for @var{nel} wisely. The method @@ -285,6 +306,9 @@ table in use or the program runs out of memory. @comment search.h @comment SVID @deftypefun void hdestroy (void) +@safety{@prelim{}@mtunsafe{@mtasurace{:hsearch}}@asunsafe{@ascuheap{}}@acunsafe{@acucorrupt{} @acsmem{}}} +@c hdestroy @mtasurace:hsearch @ascuheap @acucorrupt @acsmem +@c hdestroy_r dup @mtsrace:htab @ascuheap @acucorrupt @acsmem The @code{hdestroy} function can be used to free all the resources allocated in a previous call of @code{hcreate}. After a call to this function it is again possible to call @code{hcreate} and allocate a new @@ -328,6 +352,9 @@ this element might stay undefined since it is not used. @comment search.h @comment SVID @deftypefun {ENTRY *} hsearch (ENTRY @var{item}, ACTION @var{action}) +@safety{@prelim{}@mtunsafe{@mtasurace{:hsearch}}@asunsafe{}@acunsafe{@acucorrupt{/action==ENTER}}} +@c hsearch @mtasurace:hsearch @acucorrupt/action==ENTER +@c hsearch_r dup @mtsrace:htab @acucorrupt/action==ENTER To search in a hashing table created using @code{hcreate} the @code{hsearch} function must be used. This function can perform simple search for an element (if @var{action} has the @code{FIND}) or it can @@ -358,6 +385,24 @@ members should be changed directly. @comment search.h @comment GNU @deftypefun int hcreate_r (size_t @var{nel}, struct hsearch_data *@var{htab}) +@safety{@prelim{}@mtsafe{@mtsrace{:htab}}@asunsafe{@ascuheap{}}@acunsafe{@acucorrupt{} @acsmem{}}} +@c Unlike the lsearch array, the htab is (at least in part) opaque, so +@c let's make it absolutely clear that ensuring exclusive access is a +@c caller responsibility. + +@c Cancellation is unlikely to leave the htab in a corrupt state: the +@c last field to be initialized is the one that tells whether the entire +@c data structure was initialized, and there's a function call (calloc) +@c in between that will often ensure all other fields are written before +@c the table. However, should this call be inlined (say with LTO), this +@c assumption may not hold. The calloc call doesn't cross our library +@c interface barrier, so let's consider this could happen and mark this +@c with @acucorrupt. It's no safety loss, since we already have +@c @ascuheap anyway... + +@c hcreate_r @mtsrace:htab @ascuheap @acucorrupt @acsmem +@c isprime ok +@c calloc dup @ascuheap @acsmem The @code{hcreate_r} function initializes the object pointed to by @var{htab} to contain a hashing table with at least @var{nel} elements. So this function is equivalent to the @code{hcreate} function except @@ -376,6 +421,16 @@ programs ran out of memory. @comment search.h @comment GNU @deftypefun void hdestroy_r (struct hsearch_data *@var{htab}) +@safety{@prelim{}@mtsafe{@mtsrace{:htab}}@asunsafe{@ascuheap{}}@acunsafe{@acucorrupt{} @acsmem{}}} +@c The table is released while the table pointer still points to it. +@c Async cancellation is thus unsafe, but it already was because we call +@c free(). Using the table in a handler while it's being released would +@c also be dangerous, but calling free() already makes it unsafe, and +@c the requirement on the caller to ensure exclusive access already +@c guarantees this doesn't happen, so we don't get @asucorrupt. + +@c hdestroy_r @mtsrace:htab @ascuheap @acucorrupt @acsmem +@c free dup @ascuheap @acsmem The @code{hdestroy_r} function frees all resources allocated by the @code{hcreate_r} function for this very same object @var{htab}. As for @code{hdestroy} it is the programs responsibility to free the strings @@ -385,6 +440,13 @@ for the elements of the table. @comment search.h @comment GNU @deftypefun int hsearch_r (ENTRY @var{item}, ACTION @var{action}, ENTRY **@var{retval}, struct hsearch_data *@var{htab}) +@safety{@prelim{}@mtsafe{@mtsrace{:htab}}@assafe{}@acunsafe{@acucorrupt{/action==ENTER}}} +@c Callers have to ensure mutual exclusion; insertion, if cancelled, +@c leaves the table in a corrupt state. + +@c hsearch_r @mtsrace:htab @acucorrupt/action==ENTER +@c strlen dup ok +@c strcmp dup ok The @code{hsearch_r} function is equivalent to @code{hsearch}. The meaning of the first two arguments is identical. But instead of operating on a single global hashing table the function works on the @@ -436,6 +498,12 @@ in the header file @file{search.h}. @comment search.h @comment SVID @deftypefun {void *} tsearch (const void *@var{key}, void **@var{rootp}, comparison_fn_t @var{compar}) +@safety{@prelim{}@mtsafe{@mtsrace{:rootp}}@asunsafe{@ascuheap{}}@acunsafe{@acucorrupt{} @acsmem{}}} +@c The tree is not modified in a thread-safe manner, and rotations may +@c leave the tree in an inconsistent state that could be observed in an +@c asynchronous signal handler (except for the caller-synchronization +@c requirement) or after asynchronous cancellation of the thread +@c performing the rotation or the insertion. The @code{tsearch} function searches in the tree pointed to by @code{*@var{rootp}} for an element matching @var{key}. The function pointed to by @var{compar} is used to determine whether two elements @@ -465,6 +533,7 @@ of space @code{NULL} is returned. @comment search.h @comment SVID @deftypefun {void *} tfind (const void *@var{key}, void *const *@var{rootp}, comparison_fn_t @var{compar}) +@safety{@prelim{}@mtsafe{@mtsrace{:rootp}}@assafe{}@acsafe{}} The @code{tfind} function is similar to the @code{tsearch} function. It locates an element matching the one pointed to by @var{key} and returns a pointer to this element. But if no matching element is available no @@ -479,6 +548,7 @@ elements. @comment search.h @comment SVID @deftypefun {void *} tdelete (const void *@var{key}, void **@var{rootp}, comparison_fn_t @var{compar}) +@safety{@prelim{}@mtsafe{@mtsrace{:rootp}}@asunsafe{@ascuheap{}}@acunsafe{@acucorrupt{} @acsmem{}}} To remove a specific element matching @var{key} from the tree @code{tdelete} can be used. It locates the matching element using the same method as @code{tfind}. The corresponding element is then removed @@ -492,6 +562,7 @@ is deleted @code{tdelete} returns some unspecified value not equal to @comment search.h @comment GNU @deftypefun void tdestroy (void *@var{vroot}, __free_fn_t @var{freefct}) +@safety{@prelim{}@mtsafe{}@asunsafe{@ascuheap{}}@acunsafe{@acsmem{}}} If the complete search tree has to be removed one can use @code{tdestroy}. It frees all resources allocated by the @code{tsearch} function to generate the tree pointed to by @var{vroot}. @@ -546,6 +617,7 @@ The current node is a leaf. @comment search.h @comment SVID @deftypefun void twalk (const void *@var{root}, __action_fn_t @var{action}) +@safety{@prelim{}@mtsafe{@mtsrace{:root}}@assafe{}@acsafe{}} For each node in the tree with a node pointed to by @var{root}, the @code{twalk} function calls the function provided by the parameter @var{action}. For leaf nodes the function is called exactly once with |