From ee6fb9d0f79630af93784d58904a77be7e6a5914 Mon Sep 17 00:00:00 2001
From: Jan Gorecki <j.gorecki@wit.edu.pl>
Date: Fri, 17 Oct 2025 09:02:44 +0200
Subject: [PATCH 1/2] benchmarks

---
 R/utils.R        | 10 ++++++
 src/data.table.h |  2 ++
 src/init.c       |  1 +
 src/omp-flags.c  | 80 ++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 93 insertions(+)
 create mode 100644 src/omp-flags.c

diff --git a/R/utils.R b/R/utils.R
index 39a623b36d..5279a1a725 100644
--- a/R/utils.R
+++ b/R/utils.R
@@ -227,3 +227,13 @@ formula_vars = function(f, x) { # .formula2varlist is not API and seems to have
     attr(terms, "term.labels")
   )
 }
+
+omp_flags = function(variant, len, halt, th) {
+  th = as.integer(th)
+  halt = as.integer(halt)
+  len = as.integer(len)
+  variant = as.integer(variant)
+  stopifnot(is.integer(th))
+  stopifnot(th <= parallel::detectCores(), th > 0L)
+  .Call("Cbenchmark_omp_flagR", variant, len, halt, th)
+}
diff --git a/src/data.table.h b/src/data.table.h
index 775d492aac..75c38864f3 100644
--- a/src/data.table.h
+++ b/src/data.table.h
@@ -410,3 +410,5 @@ SEXP dt_has_zlib(void);
 SEXP startsWithAny(SEXP, SEXP, SEXP);
 SEXP convertDate(SEXP, SEXP);
 SEXP fastmean(SEXP);
+
+SEXP benchmark_omp_flagR(SEXP, SEXP, SEXP, SEXP);
diff --git a/src/init.c b/src/init.c
index ef81a7a0e0..c8870ca12e 100644
--- a/src/init.c
+++ b/src/init.c
@@ -160,6 +160,7 @@ R_CallMethodDef callMethods[] = {
 {"CmemcpyDTadaptive", (DL_FUNC)&memcpyDTadaptive, -1},
 {"Csetgrowable", (DL_FUNC)&setgrowable, -1},
 {"Cfrolladapt", (DL_FUNC)&frolladapt, -1},
+{"Cbenchmark_omp_flagR", (DL_FUNC)&benchmark_omp_flagR, -1},
 {NULL, NULL, 0}
 };
 
diff --git a/src/omp-flags.c b/src/omp-flags.c
new file mode 100644
index 0000000000..121d199736
--- /dev/null
+++ b/src/omp-flags.c
@@ -0,0 +1,80 @@
+#include "data.table.h"
+
+void benchmark_omp_flag(const int variant, int len, int halt, int th, int *cnt) {
+  if (variant == 1) {
+    // plain as is now
+    bool skip = false;
+    #pragma omp parallel for num_threads(th)
+    for (int i=0; i<len; i++) {
+      if (skip)
+        continue;
+      int tid = omp_get_thread_num(); 
+      cnt[tid]++;
+      if (i == halt)
+        skip = true;
+    }
+  } else if (variant == 2) {
+    // volatile
+    volatile bool skip = false;
+    #pragma omp parallel for num_threads(th)
+    for (int i=0; i<len; i++) {
+      if (skip)
+        continue;
+      int tid = omp_get_thread_num(); 
+      cnt[tid]++;
+      if (i == halt)
+        skip = true;
+    }
+  } else if (variant == 3) {
+    // volatile and shared
+    volatile bool skip = false;
+    #pragma omp parallel for num_threads(th) shared(skip)
+    for (int i=0; i<len; i++) {
+      if (skip)
+        continue;
+      int tid = omp_get_thread_num(); 
+      cnt[tid]++;
+      if (i == halt)
+        skip = true;
+    }
+  } else if (variant == 4) {
+    // atomic write
+    bool skip = false;
+    #pragma omp parallel for num_threads(th) shared(skip)
+    for (int i=0; i<len; i++) {
+      if (skip)
+        continue;
+      int tid = omp_get_thread_num(); 
+      cnt[tid]++;
+      if (i == halt) {
+        #pragma omp atomic write
+        skip = true;
+      }
+    }
+  } else if (variant == 5) {
+    // atomic read and atomic write
+    bool skip = false;
+    #pragma omp parallel for num_threads(th) shared(skip)
+    for (int i=0; i<len; i++) {
+      bool local_skip;
+      #pragma omp atomic read
+      local_skip = skip;
+      if (local_skip)
+          continue;
+      int tid = omp_get_thread_num(); 
+      cnt[tid]++;
+      if (i == halt) {
+        #pragma omp atomic write
+        skip = true;
+      }
+    }
+  }
+}
+
+SEXP benchmark_omp_flagR(SEXP variant, SEXP len, SEXP halt, SEXP th) {
+  SEXP ans = PROTECT(allocVector(INTSXP, INTEGER_RO(th)[0]));
+  for (int i=0; i<INTEGER_RO(th)[0]; i++) INTEGER(ans)[i] = 0;
+  benchmark_omp_flag(INTEGER_RO(variant)[0], INTEGER_RO(len)[0], INTEGER_RO(halt)[0]-1, INTEGER_RO(th)[0], INTEGER(ans));
+  UNPROTECT(1);
+  return(ans);
+}

From e023ba3d195df90ce871ceb061509378cc4e983a Mon Sep 17 00:00:00 2001
From: Jan Gorecki <J.Gorecki@wit.edu.pl>
Date: Fri, 17 Oct 2025 19:44:32 +0200
Subject: [PATCH 2/2] Update src/omp-flags.c

Co-authored-by: Benjamin Schwendinger <52290390+ben-schwen@users.noreply.github.com>
---
 src/omp-flags.c | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/src/omp-flags.c b/src/omp-flags.c
index 121d199736..e77678a31c 100644
--- a/src/omp-flags.c
+++ b/src/omp-flags.c
@@ -68,6 +68,33 @@ void benchmark_omp_flag(const int variant, int len, int halt, int th, int *cnt)
         skip = true;
       }
     }
+  } else if (variant == 6) {
+    // reduction-based approach
+    bool skip = false;
+    #pragma omp parallel for num_threads(th) reduction(||:skip)
+    for (int i=0; i<len; i++) {
+      if (skip)
+        continue;
+      int tid = omp_get_thread_num(); 
+      cnt[tid]++;
+      if (i == halt) {
+        skip = true;
+      }
+    }
+  } else if (variant == 7) {
+    // cancellation with flag
+    bool skip = false;
+    #pragma omp parallel for num_threads(th) shared(skip)
+    for (int i=0; i<len; i++) {
+      #pragma omp cancellation point for
+      int tid = omp_get_thread_num(); 
+      cnt[tid]++;
+      if (i == halt) {
+        #pragma omp atomic write
+        skip = true;
+        #pragma omp cancel for
+      }
+    }
   }
 }