Adding possibility of pinning libe3 to specific CPU cores

VERSION

@@ -1 +1 @@
-0.2.0
+0.2.1

include/libe3/c_api.h

@@ -179,6 +179,9 @@ typedef struct {
     size_t io_threads;    /* 0=default */
     int log_level;        /* -1=default */
     const char* log_path; /* NULL=auto (/tmp/e3_<role>[_<id>]_<euid>.log) */
+    /* A flag rather than a sentinel: core 0 is a legitimate target. */
+    int pin_io_threads;      /* 0=no pinning */
+    int io_thread_affinity;  /* logical core; Linux only, best-effort */
 } e3_config_t;
 
 /**

src/c_api.cpp

@@ -207,6 +207,9 @@ e3_agent_handle_t* e3_agent_create_with_config(const e3_config_t* config) {
             if (config->io_threads != 0) cfg.io_threads = config->io_threads;
             if (config->log_level >= 0) cfg.log_level = config->log_level;
             if (config->log_path) cfg.log_path = config->log_path;
+            // Gated by the flag, not a sentinel: core 0 is a real target.
+            if (config->pin_io_threads)
+                cfg.io_thread_affinity = config->io_thread_affinity;
         }
         e3_agent_handle_t* h = new e3_agent_handle_s();
         h->agent = std::make_unique<E3Agent>(std::move(cfg));

src/core/e3_interface.cpp

@@ -12,9 +12,11 @@
 #include "libe3/logger.hpp"
 #include "libe3/latrec.h"
 #include <cctype>
+#include <cerrno>
 #include <chrono>
 #include <cstdio>
 #include <cstdlib>
+#include <cstring>
 #include <signal.h>
 #include <string>
 
@@ -79,17 +81,26 @@ void apply_thread_config(int affinity, int niceness, const char* role) noexcept
         cpu_set_t cpuset;
         CPU_ZERO(&cpuset);
         CPU_SET(static_cast<size_t>(affinity), &cpuset);
-        // Non-fatal if this fails (e.g. core index out of range).
-        (void)pthread_setaffinity_np(pthread_self(),
-                                     sizeof(cpu_set_t), &cpuset);
+        // Non-fatal, but say so: a silent miss looks identical to a working pin.
+        int rc = pthread_setaffinity_np(pthread_self(), sizeof(cpu_set_t), &cpuset);
+        if (rc != 0) {
+            E3_LOG_WARN(LOG_TAG) << "Failed to pin " << role << " thread to core "
+                                 << affinity << ": " << std::strerror(rc)
+                                 << " (thread left unpinned)";
+        } else {
+            E3_LOG_INFO(LOG_TAG) << "Pinned " << role << " thread to core " << affinity;
+        }
     }
     if (niceness != 0) {
         // Use the kernel TID so only this thread's scheduling priority changes.
         // syscall(SYS_gettid) returns the kernel thread ID as a long; cast it
         // to pid_t first, then to the id_t expected by setpriority(PRIO_PROCESS).
         auto tid = static_cast<id_t>(static_cast<pid_t>(syscall(SYS_gettid)));
         // Non-fatal: negative values require CAP_SYS_NICE.
-        (void)setpriority(PRIO_PROCESS, tid, niceness);
+        if (setpriority(PRIO_PROCESS, tid, niceness) == -1) {
+            E3_LOG_WARN(LOG_TAG) << "Failed to set niceness " << niceness << " on "
+                                 << role << " thread: " << std::strerror(errno);
+        }
     }
 #else
     (void)affinity;