libc: add glibc-compatible tdestroy(3)

The function clears the whole tree.

Relnotes: yes
Reviewed by: alc, emaste
Discussed with: dougm
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differ

libc: add glibc-compatible tdestroy(3)

The function clears the whole tree.

Relnotes: yes
Reviewed by: alc, emaste
Discussed with: dougm
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D54365

show more ...

Remove $FreeBSD$: one-line .h pattern

Remove /^\s*\*+\s*\$FreeBSD\$.*$\n/

libc: add glibc-compatible tdestroy(3)

The function clears the whole tree.

Relnotes: yes
Reviewed by: alc, emaste
Discussed with: dougm
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differ

libc: add glibc-compatible tdestroy(3)

The function clears the whole tree.

Relnotes: yes
Reviewed by: alc, emaste
Discussed with: dougm
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D54365

show more ...

Remove $FreeBSD$: one-line .h pattern

Remove /^\s*\*+\s*\$FreeBSD\$.*$\n/

Merge ^/head r306906 through r307382.

Improve typing of POSIX search tree functions.

Back in 2015 when I reimplemented these functions to use an AVL tree, I
was annoyed by the weakness of the typing of these functions. Both tree
nodes a

Improve typing of POSIX search tree functions.

Back in 2015 when I reimplemented these functions to use an AVL tree, I
was annoyed by the weakness of the typing of these functions. Both tree
nodes and keys are represented by 'void *', meaning that things like the
documentation for these functions are an absolute train wreck.

To make things worse, users of these functions need to cast the return
value of tfind()/tsearch() from 'void *' to 'type_of_key **' in order to
access the key. Technically speaking such casts violate aliasing rules.
I've observed actual breakages as a result of this by enabling features
like LTO.

I've filed a bug report at the Austin Group. Looking at the way the bug
got resolved, they made a pretty good step in the right direction. A new
type 'posix_tnode' has been added to correspond to tree nodes. It is
still defined as 'void' for source-level compatibility, but in the very
far future it could be replaced by a proper structure type containing a
key pointer.

MFC after: 1 month
Differential Revision: https://reviews.freebsd.org/D8205

show more ...

MFH r289384-r293170

Sponsored by: The FreeBSD Foundation

Mfh r292839

Replace implementation of hsearch() by one that scales.

Traditionally the hcreate() function creates a hash table that uses
chaining, using a fixed user-provided size. The problem with this
approach

Replace implementation of hsearch() by one that scales.

Traditionally the hcreate() function creates a hash table that uses
chaining, using a fixed user-provided size. The problem with this
approach is that this often either wastes memory (table too big) or
yields bad performance (table too small). For applications it may not
always be easy to estimate the right hash table size. A fixed number
only increases performance compared to a linked list by a constant
factor.

This problem can be solved easily by dynamically resizing the hash
table. If the size of the hash table is at least doubled, this has no
negative on the running time complexity. If a dynamically sized hash
table is used, we can also switch to using open addressing instead of
chaining, which has the advantage of just using a single allocation for
the entire table, instead of allocating many small objects.

Finally, a problem with the existing implementation is that its
deterministic algorithm for hashing makes it possible to come up with
fixed patterns to trigger an excessive number of collisions. We can
easily solve this by using FNV-1a as a hashing algorithm in combination
with a randomly generated offset basis.

Measurements have shown that this implementation is about 20-25% faster
than the existing implementation (even if the existing implementation is
given an excessive number of buckets). Though it allocates more memory
through malloc() than the old implementation (between 4-8 pointers per
used entry instead of 3), process memory use is similar to the old
implementation as if the estimated size was underestimated by a factor
10. This is due to the fact that malloc() needs to perform less
bookkeeping.

Reviewed by: jilles, pfg
Obtained from: https://github.com/NuxiNL/cloudlibc
Differential Revision: https://reviews.freebsd.org/D4644

show more ...

Let tsearch()/tdelete() use an AVL tree.

The existing implementations of POSIX tsearch() and tdelete() don't
attempt to perform any balancing at all. Testing reveals that inserting
100k nodes into a

Let tsearch()/tdelete() use an AVL tree.

The existing implementations of POSIX tsearch() and tdelete() don't
attempt to perform any balancing at all. Testing reveals that inserting
100k nodes into a tree sequentially takes approximately one minute on my
system.

Though most other BSDs also don't use any balanced tree internally, C
libraries like glibc and musl do provide better implementations. glibc
uses a red-black tree and musl uses an AVL tree.

Red-black trees have the advantage over AVL trees that they only require
O(1) rotations after insertion and deletion, but have the disadvantage
that the tree has a maximum depth of 2*log2(n) instead of 1.44*log2(n).
My take is that it's better to focus on having a lower maximum depth,
for the reason that in the case of tsearch() the invocation of the
comparator likely dominates the running time.

This change replaces the tsearch() and tdelete() functions by versions
that create an AVL tree. Compared to musl's implementation, this version
is different in two different ways:

- We don't keep track of heights; just balances. This is sufficient.
This has the advantage that it reduces the number of nodes that are
being accessed. Storing heights requires us to also access all of the
siblings along the path.

- Don't use any recursion at all. We know that the tree cannot 2^64
elements in size, so the height of the tree can never be larger than
96. Use a 128-bit bitmask to keep track of the path that is computed.
This allows us to iterate over the same path twice, meaning we can
apply rotations from top to bottom.

Inserting 100k nodes into a tree now only takes 0.015 seconds. Insertion
seems to be twice as fast as glibc, whereas deletion has about the same
performance. Unlike glibc, it uses a fixed amount of memory.

I also experimented with both recursive and iterative bottom-up
implementations of the same algorithm. This iterative top-down version
performs similar to the recursive bottom-up version in terms of speed
and code size.

For some reason, the iterative bottom-up algorithm was actually 30%
faster for deletion, but has a quadratic memory complexity to keep track
of all the parent pointers.

Reviewed by: jilles
Obtained from: https://github.com/NuxiNL/cloudlibc
Differential Revision: https://reviews.freebsd.org/D4412

show more ...

IFC @r269962

Submitted by: Anish Gupta (akgupt3@gmail.com)

Merge head from 7/28

Sync to HEAD@r269943.

Add re-entrant versions of the hash functions based on the GNU api.

While testing this I found a conformance issue in hdestroy()
that will be fixed in a subsequent commit.

Obtained from: NetBSD (hc

Add re-entrant versions of the hash functions based on the GNU api.

While testing this I found a conformance issue in hdestroy()
that will be fixed in a subsequent commit.

Obtained from: NetBSD (hcreate.c, CVS Rev. 1.7)

show more ...

Revert r268826:
The current ordering of this header is a feature as it
is more consistent with POSIX.
Also adding gratuitous newlines is not elegant.

Pointed out by: bde

Minor sorting to match the NetBSD header

MFC after: 3 days
Obtained from: NetBSD

Merge ^/head r306906 through r307382.

Improve typing of POSIX search tree functions.

Back in 2015 when I reimplemented these functions to use an AVL tree, I
was annoyed by the weakness of the typing of these functions. Both tree
nodes a

Improve typing of POSIX search tree functions.

Back in 2015 when I reimplemented these functions to use an AVL tree, I
was annoyed by the weakness of the typing of these functions. Both tree
nodes and keys are represented by 'void *', meaning that things like the
documentation for these functions are an absolute train wreck.

To make things worse, users of these functions need to cast the return
value of tfind()/tsearch() from 'void *' to 'type_of_key **' in order to
access the key. Technically speaking such casts violate aliasing rules.
I've observed actual breakages as a result of this by enabling features
like LTO.

I've filed a bug report at the Austin Group. Looking at the way the bug
got resolved, they made a pretty good step in the right direction. A new
type 'posix_tnode' has been added to correspond to tree nodes. It is
still defined as 'void' for source-level compatibility, but in the very
far future it could be replaced by a proper structure type containing a
key pointer.

MFC after: 1 month
Differential Revision: https://reviews.freebsd.org/D8205

show more ...

MFH r289384-r293170

Sponsored by: The FreeBSD Foundation

Mfh r292839

Replace implementation of hsearch() by one that scales.

Traditionally the hcreate() function creates a hash table that uses
chaining, using a fixed user-provided size. The problem with this
approach

Replace implementation of hsearch() by one that scales.

Traditionally the hcreate() function creates a hash table that uses
chaining, using a fixed user-provided size. The problem with this
approach is that this often either wastes memory (table too big) or
yields bad performance (table too small). For applications it may not
always be easy to estimate the right hash table size. A fixed number
only increases performance compared to a linked list by a constant
factor.

This problem can be solved easily by dynamically resizing the hash
table. If the size of the hash table is at least doubled, this has no
negative on the running time complexity. If a dynamically sized hash
table is used, we can also switch to using open addressing instead of
chaining, which has the advantage of just using a single allocation for
the entire table, instead of allocating many small objects.

Finally, a problem with the existing implementation is that its
deterministic algorithm for hashing makes it possible to come up with
fixed patterns to trigger an excessive number of collisions. We can
easily solve this by using FNV-1a as a hashing algorithm in combination
with a randomly generated offset basis.

Measurements have shown that this implementation is about 20-25% faster
than the existing implementation (even if the existing implementation is
given an excessive number of buckets). Though it allocates more memory
through malloc() than the old implementation (between 4-8 pointers per
used entry instead of 3), process memory use is similar to the old
implementation as if the estimated size was underestimated by a factor
10. This is due to the fact that malloc() needs to perform less
bookkeeping.

Reviewed by: jilles, pfg
Obtained from: https://github.com/NuxiNL/cloudlibc
Differential Revision: https://reviews.freebsd.org/D4644

show more ...

Let tsearch()/tdelete() use an AVL tree.

The existing implementations of POSIX tsearch() and tdelete() don't
attempt to perform any balancing at all. Testing reveals that inserting
100k nodes into a

Let tsearch()/tdelete() use an AVL tree.

The existing implementations of POSIX tsearch() and tdelete() don't
attempt to perform any balancing at all. Testing reveals that inserting
100k nodes into a tree sequentially takes approximately one minute on my
system.

Though most other BSDs also don't use any balanced tree internally, C
libraries like glibc and musl do provide better implementations. glibc
uses a red-black tree and musl uses an AVL tree.

Red-black trees have the advantage over AVL trees that they only require
O(1) rotations after insertion and deletion, but have the disadvantage
that the tree has a maximum depth of 2*log2(n) instead of 1.44*log2(n).
My take is that it's better to focus on having a lower maximum depth,
for the reason that in the case of tsearch() the invocation of the
comparator likely dominates the running time.

This change replaces the tsearch() and tdelete() functions by versions
that create an AVL tree. Compared to musl's implementation, this version
is different in two different ways:

- We don't keep track of heights; just balances. This is sufficient.
This has the advantage that it reduces the number of nodes that are
being accessed. Storing heights requires us to also access all of the
siblings along the path.

- Don't use any recursion at all. We know that the tree cannot 2^64
elements in size, so the height of the tree can never be larger than
96. Use a 128-bit bitmask to keep track of the path that is computed.
This allows us to iterate over the same path twice, meaning we can
apply rotations from top to bottom.

Inserting 100k nodes into a tree now only takes 0.015 seconds. Insertion
seems to be twice as fast as glibc, whereas deletion has about the same
performance. Unlike glibc, it uses a fixed amount of memory.

I also experimented with both recursive and iterative bottom-up
implementations of the same algorithm. This iterative top-down version
performs similar to the recursive bottom-up version in terms of speed
and code size.

For some reason, the iterative bottom-up algorithm was actually 30%
faster for deletion, but has a quadratic memory complexity to keep track
of all the parent pointers.

Reviewed by: jilles
Obtained from: https://github.com/NuxiNL/cloudlibc
Differential Revision: https://reviews.freebsd.org/D4412

show more ...

IFC @r269962

Submitted by: Anish Gupta (akgupt3@gmail.com)

Merge head from 7/28

Sync to HEAD@r269943.