lib: correctly guard random number generation when run threaded

As random number generator tracks its internal state as a static
variable, it is necessary to guard its updates with mutex to
prevent misbehavour when multiple threads change values simultaneously

Author: marisn

lib/gis/CMakeLists.txt

@@ -4,7 +4,13 @@ if(NOT WIN32)
   list(FILTER gislib_SRCS EXCLUDE REGEX [[.*/fmode\.c$]])
 endif()
 
+find_package(Threads)
+
 set(grass_gis_DEFS "-DGRASS_VERSION_DATE=\"${GRASS_VERSION_DATE}\"")
+if(Threads_FOUND)
+  list(APPEND grass_gis_DEFS "HAVE_PTHREAD")
+endif()
+
 if(MSVC)
   set(grass_gis_DEFS "${grass_gis_DEFS};-D_USE_MATH_DEFINES=1")
   set(gislib_INCLUDES "../../msvc")

lib/gis/Makefile

@@ -2,7 +2,7 @@ MODULE_TOPDIR = ../..
 
 LIB = GIS
 
-LIBES = $(OPENMP_LIBPATH) $(OPENMP_LIB)
+LIBES = $(OPENMP_LIBPATH) $(OPENMP_LIB) $(PTHREADLIB)
 EXTRA_INC = $(ZLIBINCPATH) $(BZIP2INCPATH) $(ZSTDINCPATH) $(PTHREADINCPATH) $(REGEXINCPATH) $(OPENMP_INCPATH)
 EXTRA_CFLAGS = $(OPENMP_CFLAGS) -DGRASS_VERSION_DATE=\"'$(GRASS_VERSION_DATE)'\"
 

lib/gis/lrand48.c

@@ -3,12 +3,12 @@
  *
  * \brief GIS Library - Pseudo-random number generation
  *
- * (C) 2014 by the GRASS Development Team
+ * (C) 2014, 2025 by the GRASS Development Team
  *
  * This program is free software under the GNU General Public License
  * (>=v2). Read the file COPYING that comes with GRASS for details.
  *
- * \author Glynn Clements
+ * \authors Glynn Clements, Maris Nartiss (thread safety)
  */
 
 #include <stdio.h>
@@ -19,6 +19,10 @@
 #include <grass/gis.h>
 #include <grass/glocale.h>
 
+#ifdef HAVE_PTHREAD
+#include <pthread.h>
+#endif
+
 #ifdef HAVE_GETTIMEOFDAY
 #include <sys/time.h>
 #else
@@ -41,22 +45,36 @@ static const uint32 b0 = 0xB;
 
 static int seeded;
 
+#ifdef HAVE_PTHREAD
+static pthread_mutex_t lrand48_mutex = PTHREAD_MUTEX_INITIALIZER;
+#endif
+
 #define LO(x) ((x) & 0xFFFFU)
 #define HI(x) ((x) >> 16)
 
 /*!
  * \brief Seed the pseudo-random number generator
  *
  * \param[in] seedval 32-bit integer used to seed the PRNG
+ *
+ * This function is thread-safe.
  */
 void G_srand48(long seedval)
 {
     uint32 x = (uint32) * (unsigned long *)&seedval;
 
+#ifdef HAVE_PTHREAD
+    pthread_mutex_lock(&lrand48_mutex);
+#endif
+
     x2 = (uint16)HI(x);
     x1 = (uint16)LO(x);
     x0 = (uint16)0x330E;
     seeded = 1;
+
+#ifdef HAVE_PTHREAD
+    pthread_mutex_unlock(&lrand48_mutex);
+#endif
 }
 
 /*!
@@ -65,6 +83,8 @@ void G_srand48(long seedval)
  * A weak hash of the current time and PID is generated and used to
  * seed the PRNG
  *
+ * This function is thread-safe.
+ *
  * \return generated seed value passed to G_srand48()
  */
 long G_srand48_auto(void)
@@ -104,6 +124,10 @@ long G_srand48_auto(void)
 
 static void G__next(void)
 {
+#ifdef HAVE_PTHREAD
+    pthread_mutex_lock(&lrand48_mutex);
+#endif
+
     uint32 a0x0 = a0 * x0;
     uint32 a0x1 = a0 * x1;
     uint32 a0x2 = a0 * x2;
@@ -123,11 +147,17 @@ static void G__next(void)
     x1 = (uint16)LO(y1);
     y2 += HI(y1);
     x2 = (uint16)LO(y2);
+
+#ifdef HAVE_PTHREAD
+    pthread_mutex_unlock(&lrand48_mutex);
+#endif
 }
 
 /*!
  * \brief Generate an integer in the range [0, 2^31)
  *
+ * This function is thread-safe.
+ *
  * \return the generated value
  */
 long G_lrand48(void)
@@ -142,6 +172,8 @@ long G_lrand48(void)
 /*!
  * \brief Generate an integer in the range [-2^31, 2^31)
  *
+ * This function is thread-safe.
+ *
  * \return the generated value
  */
 long G_mrand48(void)
@@ -156,6 +188,8 @@ long G_mrand48(void)
 /*!
  * \brief Generate a floating-point value in the range [0,1)
  *
+ * This function is thread-safe.
+ *
  * \return the generated value
  */
 double G_drand48(void)