Get constant time (amortized) hash table access.

job.c

@@ -21,16 +21,23 @@
 
 #include "tube.h"
 #include "job.h"
+#include "primes.h"
 #include "util.h"
 
 static unsigned long long int next_id = 1;
 
+static int cur_prime = 0;
+
 static job *all_jobs=NULL;
+static size_t all_jobs_cap = 12289; /* == primes[0] */
+static size_t all_jobs_used = 0;
+
+static void rehash();
 
 static int
 _get_job_hash_index(unsigned long long int job_id)
 {
-    return job_id % NUM_JOB_BUCKETS;
+    return job_id % all_jobs_cap;
 }
 
 static void
@@ -41,8 +48,40 @@ store_job(job j)
     index = _get_job_hash_index(j->id);
 
     j->ht_next = all_jobs[index];
-
     all_jobs[index] = j;
+    all_jobs_used++;
+
+    /* accept a load factor of 4 */
+    if (all_jobs_used > (all_jobs_cap << 2)) rehash();
+}
+
+static void
+rehash()
+{
+    job *old = all_jobs;
+    size_t old_cap = all_jobs_cap, old_used = all_jobs_used, i;
+
+    if (cur_prime >= NUM_PRIMES) return;
+
+    all_jobs_cap = primes[++cur_prime];
+    all_jobs = calloc(all_jobs_cap, sizeof(job));
+    if (!all_jobs) {
+        twarnx("Failed to allocate %d new hash buckets", all_jobs_cap);
+        --cur_prime;
+        all_jobs = old;
+        all_jobs_cap = old_cap;
+        all_jobs_used = old_used;
+        return;
+    }
+
+    for (i = 0; i < old_cap; i++) {
+        while (old[i]) {
+            job j = old[i];
+            old[i] = j->next;
+            j->next = NULL;
+            store_job(j);
+        }
+    }
 }
 
 job
@@ -116,6 +155,8 @@ job_hash_free(job j)
             }
         }
     }
+
+    all_jobs_used--;
 }
 
 void
@@ -222,8 +263,8 @@ total_jobs()
 void
 job_init()
 {
-    all_jobs = calloc(NUM_JOB_BUCKETS, sizeof(job));
+    all_jobs = calloc(all_jobs_cap, sizeof(job));
     if (!all_jobs) {
-        twarnx("Failed to allocate %d hash buckets", NUM_JOB_BUCKETS);
+        twarnx("Failed to allocate %d hash buckets", all_jobs_cap);
     }
 }

job.h

@@ -52,8 +52,6 @@ struct job {
     char body[];
 };
 
-#define NUM_JOB_BUCKETS 12289
-
 job allocate_job(int body_size);
 job make_job(unsigned int pri, unsigned int delay, unsigned int ttr,
              int body_size, tube tube);

primes.c

@@ -0,0 +1,74 @@
+/* primes.c - exponentially increasing primes */
+
+/* Copyright (C) 2008 Keith Rarick and Philotic Inc.
+
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdlib.h>
+#include "primes.h"
+
+size_t primes[] = {
+    12289,
+    24593,
+    49193,
+    98387,
+    196799,
+    393611,
+    787243,
+    1574491,
+    3148987,
+    6297979,
+    12595991,
+    25191989,
+    50383981,
+    100767977,
+    201535967,
+    403071937,
+    806143879,
+    1612287763,
+    3224575537,
+#if _LP64
+    6449151103,
+    12898302233,
+    25796604473,
+    51593208973,
+    103186417951,
+    206372835917,
+    412745671837,
+    825491343683,
+    1650982687391,
+    3301965374803,
+    6603930749621,
+    13207861499251,
+    26415722998507,
+    52831445997037,
+    105662891994103,
+    211325783988211,
+    422651567976461,
+    845303135952931,
+    1690606271905871,
+    3381212543811743,
+    6762425087623523,
+    13524850175247127,
+    27049700350494287,
+    54099400700988593,
+    108198801401977301,
+    216397602803954641,
+    432795205607909293,
+    865590411215818597,
+    1731180822431637217,
+#endif
+};
+

primes.h

@@ -0,0 +1,27 @@
+/* primes.h - exponentially increasing primes */
+
+/* Copyright (C) 2008 Keith Rarick and Philotic Inc.
+
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <stdlib.h>
+
+#if _LP64
+#define NUM_PRIMES 48
+#else
+#define NUM_PRIMES 19
+#endif
+
+extern size_t primes[];