server : consolidate slot selection into get_available_slot (#24755)

Absorb get_slot_by_id logic into get_available_slot so slot selection
is handled by a single function call. When a specific slot id is
requested, the LCP similarity check still runs to enable proper
prompt cache updates.

Assisted-by: pi:llama.cpp/Qwen3.6-27B

diff --git a/tools/server/server-context.cpp b/tools/server/server-context.cpp
index aebca306a85b89f25b89fdfa771efe3cb3288e1c..ded622cfd680ea661001ddad33cdea960c9c88d3 100644 (file)
--- a/tools/server/server-context.cpp
+++ b/tools/server/server-context.cpp
@@ -1395,11 +1395,23 @@ private:
 
         bool update_cache = false;
 
+        // if a specific slot is requested, use it (still goes through cache update logic below)
+        if (task.id_slot != -1) {
+            ret = get_slot_by_id(task.id_slot);
+            if (ret) {
+                SLT_INF(*ret, "selected slot by id (%d)\n", task.id_slot);
+            }
+        }
+
         // find the slot that has at least n% prompt similarity
-        if (ret == nullptr && slot_prompt_similarity != 0.0f) {
+        if (slot_prompt_similarity != 0.0f) {
             float sim_best = 0;
 
             for (server_slot & slot : slots) {
+                if (task.id_slot != -1 && slot.id != task.id_slot) {
+                    continue;
+                }
+
                 // skip the slot if it is not available
                 if (slot.is_processing()) {
                     continue;
@@ -1426,8 +1438,10 @@ private:
             if (ret != nullptr) {
                 const float f_keep = (sim_best*task.tokens.size()) / ret->prompt.tokens.size();
 
-                SLT_INF(*ret, "selected slot by LCP similarity, sim_best = %.3f (> %.3f thold), f_keep = %.3f\n",
-                        sim_best, slot_prompt_similarity, f_keep);
+                if (task.id_slot == -1) {
+                    SLT_INF(*ret, "selected slot by LCP similarity, sim_best = %.3f (> %.3f thold), f_keep = %.3f\n",
+                            sim_best, slot_prompt_similarity, f_keep);
+                }
 
                 // if we are about to lose a large portion of the existing context - save it in the prompt cache
                 if (f_keep < 0.5f) {
@@ -2180,10 +2194,9 @@ private:
                         }
                     }
 
-                    const int id_slot = task.id_slot;
                     const int id_task = task.id;
 
-                    server_slot * slot = id_slot != -1 ? get_slot_by_id(id_slot) : get_available_slot(task);
+                    server_slot * slot = get_available_slot(task);
 
                     //
                     // slot scheduling logic