JSPI: Add a chance for sleep() to not actually sleep (WebAssembly#7244)

Rather than return a promise, it returns an integer immediately.

Author: kripken

scripts/fuzz_shell.js

@@ -224,6 +224,34 @@ function toAddressType(table, index) {
   return index;
 }
 
+// Simple deterministic hashing, on an unsigned 32-bit seed. See e.g.
+// https://www.boost.org/doc/libs/1_55_0/doc/html/hash/reference.html#boost.hash_combine
+var hashSeed;
+
+function hasHashSeed() {
+  return hashSeed !== undefined;
+}
+
+function hashCombine(value) {
+  // hashSeed must be set before we do anything.
+  assert(hasHashSeed());
+
+  hashSeed ^= value + 0x9e3779b9 + (hashSeed << 6) + (hashSeed >>> 2);
+  return hashSeed >>> 0;
+}
+
+// Get a random 32-bit number. This is like hashCombine but does not take a
+// parameter.
+function randomBits() {
+  return hashCombine(-1);
+}
+
+// Return true with probability 1 in n. E.g. oneIn(3) returns false 2/3 of the
+// time, and true 1/3 of the time.
+function oneIn(n) {
+  return (randomBits() % n) == 0;
+}
+
 // Set up the imports.
 var tempRet0;
 var imports = {
@@ -274,7 +302,10 @@ var imports = {
 
     // Sleep a given amount of ms (when JSPI) and return a given id after that.
     'sleep': (ms, id) => {
-      if (!JSPI) {
+      // Also avoid sleeping even in JSPI mode, rarely, just to add variety
+      // here. Only do this when we have a hash seed, that is, when we are
+      // allowing randomness.
+      if (!JSPI || (hasHashSeed() && oneIn(10))) {
         return id;
       }
       return new Promise((resolve, reject) => {
@@ -371,20 +402,15 @@ function build(binary) {
   }
 }
 
-// Simple deterministic hashing, on an unsigned 32-bit seed. See e.g.
-// https://www.boost.org/doc/libs/1_55_0/doc/html/hash/reference.html#boost.hash_combine
-function hashCombine(seed, value) {
-  seed ^= value + 0x9e3779b9 + (seed << 6) + (seed >>> 2);
-  return seed >>> 0;
-}
-
 // Run the code by calling exports. The optional |ordering| parameter indicates
 // howe we should order the calls to the exports: if it is not provided, we call
 // them in the natural order, which allows our output to be compared to other
 // executions of the wasm (e.g. from wasm-opt --fuzz-exec). If |ordering| is
 // provided, it is a random seed we use to make deterministic choices on
 // the order of calls.
 /* async */ function callExports(ordering) {
+  hashSeed = ordering;
+
   // Call the exports we were told, or if we were not given an explicit list,
   // call them all.
   let relevantExports = exportsToCall || exportList;
@@ -425,13 +451,12 @@ function hashCombine(seed, value) {
       task = tasks.pop();
     } else {
       // Pick a random task.
-      ordering = hashCombine(ordering, tasks.length);
-      let i = ordering % tasks.length;
+      let i = hashCombine(tasks.length) % tasks.length;
       task = tasks.splice(i, 1)[0];
     }
 
     // Execute the task.
-    console.log('[fuzz-exec] calling ' + task.name);
+    console.log(`[fuzz-exec] calling ${task.name}${task.deferred ? ' (after defer)' : ''}`);
     let result;
     try {
       result = task.func();
@@ -451,10 +476,7 @@ function hashCombine(seed, value) {
       //       depending on each other, ensuring certain orders of execution.
       if (ordering !== undefined && !task.deferred && result &&
           typeof result == 'object' && typeof result.then === 'function') {
-        // Hash with -1 here, just to get something different than the hashing a
-        // few lines above.
-        ordering = hashCombine(ordering, -1);
-        if (ordering & 1) {
+        if (randomBits() & 1) {
           // Defer it for later. Reuse the existing task for simplicity.
           console.log(`(jspi: defer ${task.name})`);
           task.func = /* async */ () => {

test/lit/d8/fuzz_shell_sleep.wast

@@ -0,0 +1,72 @@
+(module
+  (import "fuzzing-support" "sleep" (func $sleep (param i32 i32) (result i32)))
+
+  (func $func1 (export "func1") (result i32)
+    (call $sleep
+      (i32.const 0) ;; ms (d8 always sleeps 0 anyhow)
+      (i32.const 1) ;; id
+    )
+  )
+
+  (func $func2 (export "func2") (result i32)
+    (call $sleep
+      (i32.const 0)
+      (i32.const 2)
+    )
+  )
+
+  (func $func3 (export "func3") (result i32)
+    (call $sleep
+      (i32.const 0)
+      (i32.const 3)
+    )
+  )
+
+  (func $func4 (export "func4") (result i32)
+    (call $sleep
+      (i32.const 0)
+      (i32.const 4)
+    )
+  )
+
+  (func $func5 (export "func5") (result i32)
+    (call $sleep
+      (i32.const 0)
+      (i32.const 5)
+    )
+  )
+)
+
+;; See fuzz_shell_jspi.wast for how the following works.
+;; RUN: echo "JSPI = 1;" > %t.0.js
+;; RUN: cat %S/../../../scripts/fuzz_shell.js | node -e "process.stdout.write(require('fs').readFileSync(0, 'utf-8').replace(/[/][*] async [*][/]/g, 'async').replace(/[/][*] await [*][/]/g, 'await'))" >> %t.0.js
+
+;; Replace the callExports() at the end with a call that has a random seed.
+;; RUN: cat %t.0.js | node -e "process.stdout.write(require('fs').readFileSync(0, 'utf-8').replace('callExports()', 'callExports(66)'))" > %t.js
+
+;; Run that JS shell with our wasm.
+;; RUN: wasm-opt %s -o %t.wasm -q
+;; RUN: v8 --wasm-staging %t.js -- %t.wasm | filecheck %s
+;;
+;; We should see a few cases that avoid sleeping: func2, func3, and func4 all
+;; return a result immediately, showing they do not sleep. (Note though that
+;; func2 is more because we do not have a toplevel await, see comment in
+;; fuzz_shell_jspi.wast.)
+;;
+;; CHECK: [fuzz-exec] calling func2
+;; CHECK: [fuzz-exec] note result: func2 => 2
+;; CHECK: [fuzz-exec] calling func1
+;; CHECK: (jspi: defer func1)
+;; CHECK: [fuzz-exec] calling func3
+;; CHECK: [fuzz-exec] note result: func3 => 3
+;; CHECK: [fuzz-exec] calling func1 (after defer)
+;; CHECK: (jspi: finish func1)
+;; CHECK: [fuzz-exec] note result: func1 => 1
+;; CHECK: [fuzz-exec] calling func5
+;; CHECK: (jspi: defer func5)
+;; CHECK: [fuzz-exec] calling func4
+;; CHECK: [fuzz-exec] note result: func4 => 4
+;; CHECK: [fuzz-exec] calling func5 (after defer)
+;; CHECK: (jspi: finish func5)
+;; CHECK: [fuzz-exec] note result: func5 => 5
+