Fix exponential backoff implementation and add github actions to vali…

…date it. (#17)

* test: add github action for testing.

* chore: add another action for build.

* fix the build argument.

* fix: check for overflow in attempt too.

.github/workflows/build.yml

@@ -0,0 +1,28 @@
+name: Build
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  test:
+    runs-on: ${{ matrix.os }}-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu, macos, windows]
+    steps:
+      - uses: actions/checkout@v2
+      - name: Set up JDK 8
+        uses: actions/setup-java@v2
+        with:
+          java-version: '8'
+          distribution: 'adopt'
+      - name: Validate Gradle wrapper
+        uses: gradle/wrapper-validation-action@e6e38bacfdf1a337459f332974bb2327a31aaf4b
+      - name: Build with Gradle
+        uses: gradle/gradle-build-action@937999e9cc2425eddc7fd62d1053baf041147db7
+        with:
+          arguments: shadowJar

.github/workflows/test.yml

@@ -0,0 +1,28 @@
+name: Test
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  test:
+    runs-on: ${{ matrix.os }}-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu, macos, windows]
+    steps:
+      - uses: actions/checkout@v2
+      - name: Set up JDK 8
+        uses: actions/setup-java@v2
+        with:
+          java-version: '8'
+          distribution: 'adopt'
+      - name: Validate Gradle wrapper
+        uses: gradle/wrapper-validation-action@e6e38bacfdf1a337459f332974bb2327a31aaf4b
+      - name: Test with Gradle
+        uses: gradle/gradle-build-action@937999e9cc2425eddc7fd62d1053baf041147db7
+        with:
+          arguments: test

Makefile

@@ -6,6 +6,10 @@ clean:
 build:
 	./gradlew shadowJar
 
+.PHONY: test
+test:
+	./gradlew test
+
 .PHONY: docker-example
 docker-example: build
 	cp agent/build/libs/pyroscope.jar example/

agent/src/main/java/io/pyroscope/javaagent/ExponentialBackoff.java

@@ -23,7 +23,9 @@ final class ExponentialBackoff {
     final int error() {
         attempt += 1;
         int multiplier = cap / base;
-        if ((multiplier >> attempt) > 0) {
+        // from https://docs.oracle.com/javase/specs/jls/se8/html/jls-15.html#jls-15.19
+        // "If the promoted type of the left-hand operand is int, then only the five lowest-order bits of the right-hand operand are used as the shift distance".
+        if (attempt < 32 && (multiplier >> attempt) > 0) {
             multiplier = 1 << attempt;
         }
         return random.nextInt(base * multiplier);