configurable shm size

rmw_zenoh_cpp/src/detail/zenoh_config.cpp

@@ -42,6 +42,10 @@ static const std::unordered_map<ConfigurableEntity,
 };
 
 static const char * router_check_attempts_envar = "ZENOH_ROUTER_CHECK_ATTEMPTS";
+#ifdef RMW_ZENOH_BUILD_WITH_SHARED_MEMORY
+static const char * zenoh_shm_alloc_size_envar = "ZENOH_SHM_ALLOC_SIZE";
+static const size_t zenoh_shm_alloc_size_default = 1024*1024;
+#endif
 
 rmw_ret_t _get_z_config(
   const char * envar_name,
@@ -128,4 +132,35 @@ std::optional<uint64_t> zenoh_router_check_attempts()
   // If unset, check indefinitely.
   return default_value;
 }
+
+
+#ifdef RMW_ZENOH_BUILD_WITH_SHARED_MEMORY
+///=============================================================================
+size_t zenoh_shm_alloc_size() {
+  const char * envar_value;
+
+  if (NULL != rcutils_get_env(zenoh_shm_alloc_size_envar, &envar_value)) {
+    RMW_ZENOH_LOG_ERROR_NAMED(
+      "rmw_zenoh_cpp", "Envar %s cannot be read. Report this bug.",
+      zenoh_shm_alloc_size_envar);
+    return zenoh_shm_alloc_size_default;
+  }
+
+  // If the environment variable contains a value, handle it accordingly.
+  if (envar_value[0] != '\0') {
+    const auto read_value = std::strtoull(envar_value, nullptr, 10);
+    if (read_value > 0) {
+      if (read_value > std::numeric_limits<size_t>::max()) {
+        RMW_ZENOH_LOG_ERROR_NAMED(
+          "rmw_zenoh_cpp", "Envar %s: value is too large!",
+          zenoh_shm_alloc_size_envar);
+      } else {
+        return read_value;
+      }
+    }
+  }
+
+  return zenoh_shm_alloc_size_default;
+}
+#endif
 }  // namespace rmw_zenoh_cpp

rmw_zenoh_cpp/src/detail/zenoh_config.hpp

@@ -57,6 +57,17 @@ rmw_ret_t get_z_config(const ConfigurableEntity & entity, z_owned_config_t * con
 /// @return The number of times to try connecting to a zenoh router and
 ///   std::nullopt if establishing a connection to a router is not required.
 std::optional<uint64_t> zenoh_router_check_attempts();
+
+#ifdef RMW_ZENOH_BUILD_WITH_SHARED_MEMORY
+///=============================================================================
+/// Get the amount of shared memory to be pre-allocated for Zenoh SHM operation
+/// based on the environment variable ZENOH_SHM_ALLOC_SIZE.
+/// @details The behavior is as follows:
+///   - If not set or <= 0, the default value of 1MB is returned.
+///   - Else value of environemnt variable is returned.
+/// @return The amount of shared memory to be pre-allocated for Zenoh SHM operation
+size_t zenoh_shm_alloc_size();
+#endif
 }  // namespace rmw_zenoh_cpp
 
 #endif  // DETAIL__ZENOH_CONFIG_HPP_

rmw_zenoh_cpp/src/rmw_init.cpp

@@ -41,11 +41,6 @@
 
 
 extern "C" {
-#ifdef RMW_ZENOH_BUILD_WITH_SHARED_MEMORY
-// Megabytes of SHM to reserve.
-// TODO(clalancette): Make this configurable, or get it from the configuration
-#define SHM_BUFFER_SIZE_MB 10
-#endif
 
 namespace
 {
@@ -232,7 +227,7 @@ rmw_ret_t rmw_init(const rmw_init_options_t *options, rmw_context_t *context) {
     // TODO(yuyuan): determine the default alignment
     z_alloc_alignment_t alignment = {5};
     z_owned_memory_layout_t layout;
-    z_memory_layout_new(&layout, SHM_BUFFER_SIZE_MB * 1024 * 1024, alignment);
+    z_memory_layout_new(&layout, rmw_zenoh_cpp::zenoh_shm_alloc_size(), alignment);
 
     z_owned_shm_provider_t provider;
     if (z_posix_shm_provider_new(&provider, z_loan(layout))) {