CMAKE option LIBICAL_SYNC_MODE_THREADLOCAL: Allow compiling all global variables with thread-local storage, thus avoiding the need for synchronization.

11 files changed, 81 insertions, 28 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index f5d5e52c..c568dd0b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -107,6 +107,13 @@
 #  Build with the undefined sanitizer (requires gcc or clang)
 #  Default=false
 #
+# -DLIBICAL_SYNCMODE_THREADLOCAL=[true|false]
+#  Experimental: If set to true, global variables are marked as thread-local. This allows accessing
+#  libical from multiple threads without the need for synchronization. However, any global settings
+#  must be applied per thread.
+#  If set to false, the default synchronization mechanism is applied. That is, if the pthreads library
+#  is available, it will be used, otherwise no synchronization is applied.
+#  Default: false.
 
 cmake_minimum_required(VERSION 3.11.0) #first line, to shutup a cygwin warning
 project(libical C) #CXX is optional for the bindings
@@ -736,6 +743,9 @@ if(LIBICAL_DEVMODE_UNDEFINED_SANITIZER)
   endif()
 endif()
 
+mark_as_advanced(LIBICAL_SYNCMODE_THREADLOCAL)
+libical_option(LIBICAL_SYNCMODE_THREADLOCAL "Experimental: Mark global variables as thread-local." False)
+
 libical_option(ENABLE_LTO_BUILD "Build a link-time optimized version." False)
 if(ENABLE_LTO_BUILD)
   if(CMAKE_C_COMPILER_IS_GCC)
diff --git a/config.h.cmake b/config.h.cmake
index 0e7306cc..93ac378d 100644
--- a/config.h.cmake
+++ b/config.h.cmake
@@ -583,5 +583,34 @@ typedef ssize_t IO_SSIZE_T;
 #define ICALMEMORY_DEFAULT_REALLOC realloc
 #define ICALMEMORY_DEFAULT_FREE free
 
-/* ICAL_GLOBAL_VAR is applied to global variables, therefore allows specifying custom storage attributes. */
+
+#cmakedefine LIBICAL_SYNCMODE_THREADLOCAL 1
+
+#define ICAL_SYNC_MODE_NONE 1
+#define ICAL_SYNC_MODE_PTHREAD 2
+#define ICAL_SYNC_MODE_THREADLOCAL 3
+
+#ifdef LIBICAL_SYNCMODE_THREADLOCAL
+#define ICAL_SYNC_MODE ICAL_SYNC_MODE_THREADLOCAL
+#elif HAVE_PTHREAD == 1
+#define ICAL_SYNC_MODE ICAL_SYNC_MODE_PTHREAD
+#else
+#define ICAL_SYNC_MODE ICAL_SYNC_MODE_NONE
+#endif
+
+#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_THREADLOCAL
+#if defined(_MSC_VER)
+#define ICAL_GLOBAL_VAR __declspec(thread)
+#endif
+#if defined(__GNUC__)
+#define ICAL_GLOBAL_VAR __thread
+#endif
+#ifndef ICAL_GLOBAL_VAR
+/* thread_local has been introduced with C11. Starting with C23 it will become a keyword and
+   we won't need to include threads.h then. */
+#include <threads.h>
+#define ICAL_GLOBAL_VAR thread_local
+#endif
+#else
 #define ICAL_GLOBAL_VAR
+#endif
diff --git a/src/libical/icalerror.c b/src/libical/icalerror.c
index 9692bd1e..d8a85b4c 100644
--- a/src/libical/icalerror.c
+++ b/src/libical/icalerror.c
@@ -22,7 +22,7 @@
 #include <execinfo.h>
 #endif
 
-#if defined(HAVE_PTHREAD)
+#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_PTHREAD
 #include <pthread.h>
 
 static pthread_key_t icalerrno_key;
diff --git a/src/libical/icalmemory.c b/src/libical/icalmemory.c
index f12833b3..abf98618 100644
--- a/src/libical/icalmemory.c
+++ b/src/libical/icalmemory.c
@@ -39,7 +39,7 @@ typedef struct
     void *ring[BUFFER_RING_SIZE];
 } buffer_ring;
 
-#if !defined(HAVE_PTHREAD)
+#if ICAL_SYNC_MODE != ICAL_SYNC_MODE_PTHREAD
 /**
  * @private
  */
@@ -63,7 +63,7 @@ static void icalmemory_free_ring_byval(buffer_ring * br)
     icalmemory_free_buffer(br);
 }
 
-#if defined(HAVE_PTHREAD)
+#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_PTHREAD
 #include <pthread.h>
 
 static pthread_key_t ring_key;
@@ -116,7 +116,7 @@ static buffer_ring *buffer_ring_new(void)
     return (br);
 }
 
-#if defined(HAVE_PTHREAD)
+#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_PTHREAD
 /**
  * @private
  */
@@ -156,7 +156,7 @@ static buffer_ring *get_buffer_ring_global(void)
  */
 static buffer_ring *get_buffer_ring(void)
 {
-#if defined(HAVE_PTHREAD)
+#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_PTHREAD
     return (get_buffer_ring_pthread());
 #else
     return get_buffer_ring_global();
@@ -221,7 +221,7 @@ void icalmemory_free_ring(void)
         return;
 
     icalmemory_free_ring_byval(br);
-#if defined(HAVE_PTHREAD)
+#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_PTHREAD
     pthread_setspecific(ring_key, 0);
 #else
     global_buffer_ring = 0;
diff --git a/src/libical/icalmemory.h b/src/libical/icalmemory.h
index 39541d2d..adb580da 100644
--- a/src/libical/icalmemory.h
+++ b/src/libical/icalmemory.h
@@ -120,8 +120,8 @@ LIBICAL_ICAL_EXPORT void icalmemory_add_tmp_buffer(void *buf);
 /**
  * @brief Frees all memory used in the ring
  *
- * Frees all memory used in the ring. Depending on if HAVE_PTHREAD is set or
- * not, the ring buffer is allocated on a per-thread basis, meaning that if all
+ * Frees all memory used in the ring. If PTHREAD is used or thread-local mode is configured,
+ * the ring buffer is allocated on a per-thread basis, meaning that if all
  * rings are to be released, it must be called once in every thread.
  *
  * @par Usage
diff --git a/src/libical/icalrecur.c b/src/libical/icalrecur.c
index b9c7b77d..6080bea5 100644
--- a/src/libical/icalrecur.c
+++ b/src/libical/icalrecur.c
@@ -134,7 +134,7 @@
 #include <stddef.h>     /* For offsetof() macro */
 #include <stdlib.h>
 
-#if defined(HAVE_PTHREAD)
+#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_PTHREAD
 #include <pthread.h>
 static pthread_mutex_t invalid_rrule_mutex = PTHREAD_MUTEX_INITIALIZER;
 #endif
@@ -3642,13 +3642,13 @@ ical_invalid_rrule_handling ical_get_invalid_rrule_handling_setting(void)
 {
     ical_invalid_rrule_handling myHandling;
 
-#if defined(HAVE_PTHREAD)
+#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_PTHREAD
     pthread_mutex_lock(&invalid_rrule_mutex);
 #endif
 
     myHandling = invalidRruleHandling;
 
-#if defined(HAVE_PTHREAD)
+#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_PTHREAD
     pthread_mutex_unlock(&invalid_rrule_mutex);
 #endif
 
@@ -3657,13 +3657,13 @@ ical_invalid_rrule_handling ical_get_invalid_rrule_handling_setting(void)
 
 void ical_set_invalid_rrule_handling_setting(ical_invalid_rrule_handling newSetting)
 {
-#if defined(HAVE_PTHREAD)
+#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_PTHREAD
     pthread_mutex_lock(&invalid_rrule_mutex);
 #endif
 
     invalidRruleHandling = newSetting;
 
-#if defined(HAVE_PTHREAD)
+#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_PTHREAD
     pthread_mutex_unlock(&invalid_rrule_mutex);
 #endif
 }
diff --git a/src/libical/icaltimezone.c b/src/libical/icaltimezone.c
index 60b26a0d..acaf39c2 100644
--- a/src/libical/icaltimezone.c
+++ b/src/libical/icaltimezone.c
@@ -26,7 +26,7 @@
 #include <stdlib.h>
 #include <limits.h>
 
-#if defined(HAVE_PTHREAD)
+#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_PTHREAD
 #include <pthread.h>
 #if defined(PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP)
 // It seems the same thread can attempt to lock builtin_mutex multiple times
@@ -166,28 +166,28 @@ static const char *get_zone_directory(void);
 
 static void icaltimezone_builtin_lock(void)
 {
-#if defined(HAVE_PTHREAD)
+#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_PTHREAD
     pthread_mutex_lock(&builtin_mutex);
 #endif
 }
 
 static void icaltimezone_builtin_unlock(void)
 {
-#if defined(HAVE_PTHREAD)
+#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_PTHREAD
     pthread_mutex_unlock(&builtin_mutex);
 #endif
 }
 
 static void icaltimezone_changes_lock(void)
 {
-#if defined(HAVE_PTHREAD)
+#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_PTHREAD
     pthread_mutex_lock(&changes_mutex);
 #endif
 }
 
 static void icaltimezone_changes_unlock(void)
 {
-#if defined(HAVE_PTHREAD)
+#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_PTHREAD
     pthread_mutex_unlock(&changes_mutex);
 #endif
 }
diff --git a/src/libical/icaltypes.c b/src/libical/icaltypes.c
index 95d18540..ad85ae52 100644
--- a/src/libical/icaltypes.c
+++ b/src/libical/icaltypes.c
@@ -17,7 +17,7 @@
 
 #define TMP_BUF_SIZE 1024
 
-#if defined(HAVE_PTHREAD)
+#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_PTHREAD
 #include <pthread.h>
 static pthread_mutex_t unk_token_mutex = PTHREAD_MUTEX_INITIALIZER;
 #endif
@@ -174,13 +174,13 @@ ical_unknown_token_handling ical_get_unknown_token_handling_setting(void)
 {
     ical_unknown_token_handling myHandling;
 
-#if defined(HAVE_PTHREAD)
+#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_PTHREAD
     pthread_mutex_lock(&unk_token_mutex);
 #endif
 
     myHandling = unknownTokenHandling;
 
-#if defined(HAVE_PTHREAD)
+#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_PTHREAD
     pthread_mutex_unlock(&unk_token_mutex);
 #endif
 
@@ -189,13 +189,13 @@ ical_unknown_token_handling ical_get_unknown_token_handling_setting(void)
 
 void ical_set_unknown_token_handling_setting(ical_unknown_token_handling newSetting)
 {
-#if defined(HAVE_PTHREAD)
+#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_PTHREAD
     pthread_mutex_lock(&unk_token_mutex);
 #endif
 
     unknownTokenHandling = newSetting;
 
-#if defined(HAVE_PTHREAD)
+#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_PTHREAD
     pthread_mutex_unlock(&unk_token_mutex);
 #endif
 }
diff --git a/src/libical/pvl.c b/src/libical/pvl.c
index 8faaa264..0d3e006b 100644
--- a/src/libical/pvl.c
+++ b/src/libical/pvl.c
@@ -21,7 +21,7 @@
 #include <stdlib.h>
 
 /* To mute a ThreadSanitizer claim */
-#if defined(HAVE_PTHREAD) && defined(THREAD_SANITIZER)
+#if (ICAL_SYNC_MODE == ICAL_SYNC_MODE_PTHREAD) && defined(THREAD_SANITIZER)
 #include <pthread.h>
 static pthread_mutex_t pvl_mutex = PTHREAD_MUTEX_INITIALIZER;
 
diff --git a/src/test/builtin_timezones.c b/src/test/builtin_timezones.c
index 9271bd33..24b56f6d 100644
--- a/src/test/builtin_timezones.c
+++ b/src/test/builtin_timezones.c
@@ -12,7 +12,7 @@
 #include <config.h>
 #endif
 
-#ifdef HAVE_PTHREAD_H
+#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_PTHREAD
 #include <pthread.h>
 #include <assert.h>
 #endif
@@ -21,7 +21,7 @@
 
 #include <stdio.h>
 
-#if defined(HAVE_PTHREAD_H) && defined(HAVE_PTHREAD) && defined(HAVE_PTHREAD_CREATE)
+#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_PTHREAD
 
 #define N_THREADS 20
 
@@ -82,7 +82,7 @@ int main(void)
     set_zone_directory("../../zoneinfo");
     icaltimezone_set_tzid_prefix("/softwarestudio.org/");
 
-#if defined(HAVE_PTHREAD_H) && defined(HAVE_PTHREAD) && defined(HAVE_PTHREAD_CREATE)
+#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_PTHREAD
     test_get_component_threadsafety();
 #endif
 
diff --git a/src/test/icaltm_test.c b/src/test/icaltm_test.c
index 74bea858..e98e7f6a 100644
--- a/src/test/icaltm_test.c
+++ b/src/test/icaltm_test.c
@@ -16,7 +16,9 @@
 
 #include <pthread.h>
 
+#if ICAL_SYNC_MODE != ICAL_SYNC_MODE_THREADLOCAL
 static icaltimezone *zone, *utc;
+#endif
 
 static void *test_tread(void *user_data)
 {
@@ -24,6 +26,14 @@ static void *test_tread(void *user_data)
     int ii;
 
     _unused(user_data);
+
+#if ICAL_SYNC_MODE == ICAL_SYNC_MODE_THREADLOCAL
+    // In thread-local mode all initialization must be done per thread, so we do it here, rather
+    // than in main().
+    icaltimezone* zone = icaltimezone_get_builtin_timezone("America/New_York");
+    icaltimezone* utc = icaltimezone_get_utc_timezone();
+#endif
+
     itt = icaltime_from_string("19710203T040506");
     itt.zone = zone;
 
@@ -39,8 +49,12 @@ int main(void)
     pthread_t thread[2];
     int ii;
 
+#if ICAL_SYNC_MODE != ICAL_SYNC_MODE_THREADLOCAL
+    // In thread-local mode all initialization must be done per thread.
+    // In all other modes we do the initialization of built in timezones here.
     zone = icaltimezone_get_builtin_timezone("America/New_York");
     utc = icaltimezone_get_utc_timezone();
+#endif
 
     for (ii = 0; ii < 2; ii++) {
         pthread_create(&thread[ii], NULL, test_tread, NULL);