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authorRich Felker <dalias@aerifal.cx>2011-06-29 15:29:52 -0400
committerRich Felker <dalias@aerifal.cx>2011-06-29 15:29:52 -0400
commitf7dff1852b996363061e04531a15a3403351c375 (patch)
treeaeed815eab8e766a10f0af833b8e31dc2d826073 /src/prng
parentaf3d5405b8d7b00c121643d7a0c0b9bb31cc7139 (diff)
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locking support for random() prng
these interfaces are required to be thread-safe even though they are not state-free. the random number sequence is shared across all threads.
Diffstat (limited to 'src/prng')
-rw-r--r--src/prng/random.c35
1 files changed, 28 insertions, 7 deletions
diff --git a/src/prng/random.c b/src/prng/random.c
index 4b2daef2..cc5702ed 100644
--- a/src/prng/random.c
+++ b/src/prng/random.c
@@ -7,6 +7,7 @@
#include <stdlib.h>
#include <stdint.h>
+#include "libc.h"
/*
this code uses the same lagged fibonacci generator as the
@@ -32,6 +33,7 @@ static int n = 31;
static int i = 3;
static int j = 0;
static uint32_t *x = init+1;
+static int lock;
static uint32_t lcg31(uint32_t x) {
return (1103515245*x + 12345) & 0x7fffffff;
@@ -53,7 +55,7 @@ static void loadstate(uint32_t *state) {
j = x[-1]&0xff;
}
-void srandom(unsigned seed) {
+static void __srandom(unsigned seed) {
int k;
uint64_t s = seed;
@@ -71,11 +73,20 @@ void srandom(unsigned seed) {
x[0] |= 1;
}
+void srandom(unsigned seed) {
+ LOCK(&lock);
+ __srandom(seed);
+ UNLOCK(&lock);
+}
+
char *initstate(unsigned seed, char *state, size_t size) {
- void *old = savestate();
+ void *old;
+
if (size < 8)
return 0;
- else if (size < 32)
+ LOCK(&lock);
+ old = savestate();
+ if (size < 32)
n = 0;
else if (size < 64)
n = 7;
@@ -86,26 +97,36 @@ char *initstate(unsigned seed, char *state, size_t size) {
else
n = 63;
x = (uint32_t*)state + 1;
- srandom(seed);
+ __srandom(seed);
+ UNLOCK(&lock);
return old;
}
char *setstate(char *state) {
- void *old = savestate();
+ void *old;
+
+ LOCK(&lock);
+ old = savestate();
loadstate((uint32_t*)state);
+ UNLOCK(&lock);
return old;
}
long random(void) {
long k;
- if (n == 0)
- return x[0] = lcg31(x[0]);
+ LOCK(&lock);
+ if (n == 0) {
+ k = x[0] = lcg31(x[0]);
+ goto end;
+ }
x[i] += x[j];
k = x[i]>>1;
if (++i == n)
i = 0;
if (++j == n)
j = 0;
+end:
+ UNLOCK(&lock);
return k;
}