add --race to FM

Try to uncover races by running parallel replicas.

The default --race 0 should keep FM working as before, but now with
--race ≥2 we'll actively try to race replicas, syncing between tests.
--race 1 is almost pointless, just changing the thread tests run on but
without any interesting concurrency.

Rearrange a bit how fm_driver decides what flags to pass to which
invocations of FM, so individual runs can easily override defaults (e.g.
--nativeFonts overriding the usual --nonativeFonts).  Use that here to
set --race 0 for unit tests; many unit tests are not reentrant.

Change-Id: Ida451626c093793b0805d3036beb185e7d54f27e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/376761
Reviewed-by: Brian Osman <brianosman@google.com>
Reviewed-by: Eric Boren <borenet@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>

infra/bots/task_drivers/fm_driver/fm_driver.go

@@ -397,10 +397,15 @@ func main() {
 		parts := strings.Split(*bot, "-")
 		OS, model, CPU_or_GPU := parts[1], parts[3], parts[4]
 
-		commonFlags := []string{}
+		// Bots use portable fonts except where we explicitly opt-in to native fonts.
+		defaultFlags := []string{"--nonativeFonts"}
 
 		run := func(sources []string, extraFlags string) {
-			kickoff(sources, append(strings.Fields(extraFlags), commonFlags...))
+			// Default then extra to allow overriding the defaults.
+			flags := []string{}
+			flags = append(flags, defaultFlags...)
+			flags = append(flags, strings.Fields(extraFlags)...)
+			kickoff(sources, flags)
 		}
 
 		gms := shorthands["gms"]
@@ -423,19 +428,21 @@ func main() {
 			imgs = filter(imgs, func(s string) bool { return !rawExts[normalizedExt(s)] })
 		}
 
-		if CPU_or_GPU == "CPU" {
-			commonFlags = append(commonFlags, "-b", "cpu")
+		if strings.Contains(*bot, "TSAN") {
+			// Run each test a few times in parallel to uncover races.
+			defaultFlags = append(defaultFlags, "--race", "4")
+		}
 
-			// Run GMs once using native fonts, then switch to portable fonts for everything else.
-			run(gms, "--nativeFonts true")
-			commonFlags = append(commonFlags, "--nativeFonts", "false")
+		if CPU_or_GPU == "CPU" {
+			defaultFlags = append(defaultFlags, "-b", "cpu")
 
 			// FM's default ct/gamut/tf flags are equivalent to --config srgb in DM.
 			run(gms, "")
+			run(gms, "--nativeFonts")
 			run(imgs, "")
 			run(svgs, "")
 			run(skps, "--clipW 1000 --clipH 1000")
-			run(tests, "")
+			run(tests, "--race 0") // Several unit tests are not reentrant.
 
 			if model == "GCE" {
 				run(gms, "--ct g8 --legacy")                      // --config g8

tools/fm/fm.cpp

@@ -16,6 +16,7 @@
 #include "src/core/SkColorSpacePriv.h"
 #include "src/core/SkMD5.h"
 #include "src/core/SkOSFile.h"
+#include "src/core/SkTaskGroup.h"
 #include "src/gpu/GrDirectContextPriv.h"
 #include "src/gpu/GrGpu.h"
 #include "src/utils/SkOSPath.h"
@@ -82,6 +83,7 @@ static DEFINE_int(clipH, INT_MAX, "Limit source height.");
 static DEFINE_bool   (cpuDetect, true, "Detect CPU features for runtime optimizations?");
 static DEFINE_string2(writePath, w, "", "Write .pngs to this directory if set.");
 static DEFINE_bool   (quick, false, "Skip image hashing and encoding?");
+static DEFINE_int    (race, 0, "If >0, use threads to induce race conditions?");
 
 static DEFINE_string(writeShaders, "", "Write GLSL shaders to this directory if set.");
 
@@ -372,6 +374,7 @@ extern bool gSkVMJITViaDylib;
 int main(int argc, char** argv) {
     CommandLineFlags::Parse(argc, argv);
     SetupCrashHandler();
+    SkTaskGroup::Enabler enabled(FLAGS_race);
 
     if (FLAGS_cpuDetect) {
         SkGraphics::Init();
@@ -423,8 +426,11 @@ int main(int argc, char** argv) {
         return 1;
     }
 
+    const int replicas = std::max(1, FLAGS_race);
+
     SkTArray<Source> sources;
-    for (const SkString& name : FLAGS_sources) {
+    for (const SkString& name : FLAGS_sources)
+    for (int replica = 0; replica < replicas; replica++) {
         Source* source = &sources.push_back();
         source->name = name;
 
@@ -549,7 +555,10 @@ int main(int argc, char** argv) {
                                           : SkColorSpace::MakeRGB(tf,gamut);
     const SkColorInfo color_info{ct,at,cs};
 
-    for (auto source : sources) {
+    for (int i = 0; i < sources.count(); i += replicas)
+    SkTaskGroup{}.batch(replicas, [=](int replica) {
+        Source source = sources[i+replica];
+
         AutoreleasePool pool;
         const auto start = std::chrono::steady_clock::now();
 
@@ -593,12 +602,6 @@ int main(int argc, char** argv) {
                 break;
         }
 
-        if (!image && !blob) {
-            fprintf(stdout, "%50s  skipped\n", source.name.c_str());
-            fflush(stdout);
-            continue;
-        }
-
         // We read back a bitmap even when --quick is set and we won't use it,
         // to keep us honest about deferred work, flushing pipelines, etc.
         SkBitmap bitmap;
@@ -606,6 +609,17 @@ int main(int argc, char** argv) {
             SK_ABORT("SkImage::asLegacyBitmap() failed.");
         }
 
+        // Our --race replicas have done their job by now if they're going to catch anything.
+        if (replica != 0) {
+            return;
+        }
+
+        if (!image && !blob) {
+            fprintf(stdout, "%50s  skipped\n", source.name.c_str());
+            fflush(stdout);
+            return;
+        }
+
         SkString md5;
         if (!FLAGS_quick) {
             HashAndEncode hashAndEncode{bitmap};
@@ -646,7 +660,8 @@ int main(int argc, char** argv) {
                 md5.c_str(),
                 (int)std::chrono::duration_cast<std::chrono::milliseconds>(elapsed).count());
         fflush(stdout);
-    }
+    });
+
 
     if (!FLAGS_writeShaders.isEmpty()) {
         sk_mkdir(FLAGS_writeShaders[0]);