Implement thread-safe logging.

This commit introduces thread-safe logging to rcutils.
In particular, what it does is to add in a read-write lock
around accesses to the g_rcutils_logging_severities_map
in logging.c.

This enables two things:
1. Thread-safe writes to the hash map so that get_logger_level
and set_logger_level can be called simultaneously on two
different threads.
2. The ability to cache lookups during get_logger_effective_level,
so we have to do less parsing on every log call.

This introduces the concept of locking into rcutils, which
we haven't had before.  However, this particular use seems to
be justified, since the logging subsystem can be called outside
of the client libraries that could possibly do this locking
at a higher level (think about the rmw implementations, for
instance).

Note that this introduces a new pthread dependency within
rcutils that we've not had before.

Signed-off-by: Chris Lalancette <[email protected]>

CMakeLists.txt

@@ -63,6 +63,7 @@ set(rcutils_sources
   src/process.c
   src/qsort.c
   src/repl_str.c
+  src/rwlock.c
   src/sha256.c
   src/shared_library.c
   src/snprintf.c

src/logging.c

@@ -49,6 +49,8 @@
 #include "rcutils/time.h"
 #include "rcutils/types/hash_map.h"
 
+#include "./rwlock.h"
+
 
 #define RCUTILS_LOGGING_SEPARATOR_CHAR '.'
 
@@ -90,6 +92,7 @@ static const char * g_rcutils_logging_default_output_format =
 static rcutils_allocator_t g_rcutils_logging_allocator;
 
 static rcutils_logging_output_handler_t g_rcutils_logging_output_handler = NULL;
+static rcutils_rwlock_t g_rcutils_logging_map_lock;
 static rcutils_hash_map_t g_rcutils_logging_severities_map;
 
 // If this is false, attempts to use the severities map will be skipped.
@@ -645,6 +648,10 @@ rcutils_ret_t rcutils_logging_initialize_with_allocator(rcutils_allocator_t allo
     return RCUTILS_RET_ERROR;
   }
 
+  g_rcutils_logging_map_lock = rcutils_get_zero_initialized_rwlock();
+  // TODO(clalancette): Error checking
+  rcutils_rwlock_init(&g_rcutils_logging_map_lock, allocator);
+
   parse_and_create_handlers_list();
 
   g_rcutils_logging_severities_map_valid = true;
@@ -665,6 +672,7 @@ rcutils_ret_t rcutils_logging_shutdown(void)
     // Iterate over the map, getting every key so we can free it
     char * key = NULL;
     int level;
+    rcutils_rwlock_write_lock(&g_rcutils_logging_map_lock);
     rcutils_ret_t hash_map_ret = rcutils_hash_map_get_next_key_and_data(
       &g_rcutils_logging_severities_map, NULL, &key, &level);
     while (RCUTILS_RET_OK == hash_map_ret) {
@@ -688,6 +696,9 @@ rcutils_ret_t rcutils_logging_shutdown(void)
         rcutils_get_error_string().str);
       ret = RCUTILS_RET_LOGGING_SEVERITY_MAP_INVALID;
     }
+    rcutils_rwlock_write_unlock(&g_rcutils_logging_map_lock);
+    rcutils_rwlock_fini(&g_rcutils_logging_map_lock);
+
     g_rcutils_logging_severities_map_valid = false;
   }
   g_num_log_msg_handlers = 0;
@@ -775,6 +786,18 @@ static rcutils_ret_t add_key_to_hash_map(const char * name, int level, bool set_
   // Check if key already exists, to avoid extra memory allocation
   // If the key already exists, then rcutils_hash_map_set will not maintain the key we give it,
   // so we do not need to copy the name
+  if (set_by_user) {
+    rcutils_rwlock_write_lock(&g_rcutils_logging_map_lock);
+  } else {
+    // In the specific case where this is not being set by the user, we know
+    // that this is a cache set.  Just try to get the lock here; if we fail,
+    // the worst case is that we don't cache this in the map and we'll try
+    // again next time.
+    rcutils_ret_t lockret = rcutils_rwlock_write_trylock(&g_rcutils_logging_map_lock);
+    if (lockret != RCUTILS_RET_OK) {
+      return RCUTILS_RET_OK;
+    }
+  }
   bool already_exists = rcutils_hash_map_key_exists(&g_rcutils_logging_severities_map, &copy_name);
 
   if (!already_exists) {
@@ -783,6 +806,7 @@ static rcutils_ret_t add_key_to_hash_map(const char * name, int level, bool set_
     if (copy_name == NULL) {
       // Don't report an error to the error handling machinery; some uses of this function are for
       // caching so this is not necessarily fatal.
+      rcutils_rwlock_write_unlock(&g_rcutils_logging_map_lock);
       return RCUTILS_RET_ERROR;
     }
   }
@@ -800,16 +824,21 @@ static rcutils_ret_t add_key_to_hash_map(const char * name, int level, bool set_
     RCUTILS_SET_ERROR_MSG_WITH_FORMAT_STRING(
       "Error setting severity level for logger named '%s': %s",
       name, rcutils_get_error_string().str);
+    rcutils_rwlock_write_unlock(&g_rcutils_logging_map_lock);
     return RCUTILS_RET_ERROR;
   }
 
+  rcutils_rwlock_write_unlock(&g_rcutils_logging_map_lock);
+
   return RCUTILS_RET_OK;
 }
 
 static rcutils_ret_t get_severity_level(const char * name, int * severity)
 {
+  rcutils_rwlock_read_lock(&g_rcutils_logging_map_lock);
   rcutils_ret_t ret =
     rcutils_hash_map_get(&g_rcutils_logging_severities_map, &name, severity);
+  rcutils_rwlock_read_unlock(&g_rcutils_logging_map_lock);
   if (ret != RCUTILS_RET_OK) {
     // One possible response is RCUTILS_RET_NOT_FOUND, but the higher layers may be OK with that.
     return ret;
@@ -845,7 +874,9 @@ int rcutils_logging_get_logger_leveln(const char * name, size_t name_length)
   }
 
   int severity;
+  rcutils_rwlock_read_lock(&g_rcutils_logging_map_lock);
   rcutils_ret_t ret = get_severity_level(short_name, &severity);
+  rcutils_rwlock_read_unlock(&g_rcutils_logging_map_lock);
   g_rcutils_logging_allocator.deallocate(short_name, g_rcutils_logging_allocator.state);
   if (ret != RCUTILS_RET_OK) {
     // The error message was already set by get_severity_level
@@ -863,8 +894,10 @@ int rcutils_logging_get_logger_effective_level(const char * name)
   }
 
   size_t hash_map_size;
+  rcutils_rwlock_read_lock(&g_rcutils_logging_map_lock);
   rcutils_ret_t hash_map_ret = rcutils_hash_map_get_size(
     &g_rcutils_logging_severities_map, &hash_map_size);
+  rcutils_rwlock_read_unlock(&g_rcutils_logging_map_lock);
   if (hash_map_ret != RCUTILS_RET_OK) {
     RCUTILS_SET_ERROR_MSG_WITH_FORMAT_STRING(
       "Error getting severity level for logger named '%s': %s",
@@ -943,20 +976,18 @@ int rcutils_logging_get_logger_effective_level(const char * name)
     severity = g_rcutils_logging_default_logger_level;
   }
 
-  // TODO(wjwwood): restore or replace this optimization when thread-safety is addressed
-  //   see: https://github.com/ros2/rcutils/pull/393
-  // // If the calculated severity is anything but UNSET, we place it into the hashmap for speedier
-  // // lookup next time.  If the severity is UNSET, we don't bother because we are going to have to
-  // // walk the hierarchy next time anyway.
-  // if (severity != RCUTILS_LOG_SEVERITY_UNSET) {
-  //   ret = add_key_to_hash_map(name, severity, false);
-  //   if (ret != RCUTILS_RET_OK) {
-  //     // Continue on if we failed to add the key to the hashmap.
-  //     // This will affect performance but is not fatal.
-  //     RCUTILS_SAFE_FWRITE_TO_STDERR(
-  //       "Failed to cache severity; this is not fatal but will impact performance\n");
-  //   }
-  // }
+  // If the calculated severity is anything but UNSET, we place it into the hashmap for speedier
+  // lookup next time.  If the severity is UNSET, we don't bother because we are going to have to
+  // walk the hierarchy next time anyway.
+  if (severity != RCUTILS_LOG_SEVERITY_UNSET) {
+    ret = add_key_to_hash_map(name, severity, false);
+    if (ret != RCUTILS_RET_OK) {
+      // Continue on if we failed to add the key to the hashmap.
+      // This will affect performance but is not fatal.
+      RCUTILS_SAFE_FWRITE_TO_STDERR(
+        "Failed to cache severity; this is not fatal but will impact performance\n");
+    }
+  }
 
   return severity;
 }
@@ -990,6 +1021,13 @@ rcutils_ret_t rcutils_logging_set_logger_level(const char * name, int level)
 
   size_t name_length = strlen(name);
 
+  // TODO(clalancette): We could *almost* make this a read lock, except for the fact that the loop
+  // below might unset keys.  If we find that this write lock is a bottleneck, we could split
+  // that unsetting of keys into a separate function which acquires the write lock itself.
+  // However, don't forget that when unlocking as read and relocking as write, you have to
+  // double-check that the thing you were operating on still exists (since it may have been
+  // changed in the meantime).
+  rcutils_rwlock_write_lock(&g_rcutils_logging_map_lock);
   if (rcutils_hash_map_key_exists(&g_rcutils_logging_severities_map, &name)) {
     // Iterate over the entire contents of the severities map, looking for entries that start with
     // this key name.  For any ones that match, check whether the user explicitly set them.  If the
@@ -1029,6 +1067,7 @@ rcutils_ret_t rcutils_logging_set_logger_level(const char * name, int level)
         RCUTILS_SET_ERROR_MSG_WITH_FORMAT_STRING(
           "Error accessing hash map when setting logger level for '%s': %s",
           name, rcutils_get_error_string().str);
+        rcutils_rwlock_write_unlock(&g_rcutils_logging_map_lock);
         return hash_map_ret;
       }
 
@@ -1042,12 +1081,14 @@ rcutils_ret_t rcutils_logging_set_logger_level(const char * name, int level)
           RCUTILS_SET_ERROR_MSG_WITH_FORMAT_STRING(
             "Error clearing old severity level for logger named '%s': %s",
             name, rcutils_get_error_string().str);
+          rcutils_rwlock_write_unlock(&g_rcutils_logging_map_lock);
           return unset_ret;
         }
         g_rcutils_logging_allocator.deallocate(previous_key, g_rcutils_logging_allocator.state);
       }
     }
   }
+  rcutils_rwlock_write_unlock(&g_rcutils_logging_map_lock);
 
   rcutils_ret_t add_key_ret = add_key_to_hash_map(name, level, true);
   if (add_key_ret != RCUTILS_RET_OK) {