Test java/lang/StringBuffer/ECoreIndexOf.java#id1 weas the first to timeout.

Most of the timeout handler actions failed to run, indicating the process was already gone by then (though no success was shown in the log file). The one action that did run was the core dump analysis (jstack core mixed) which simply showed:

----------------- 27395 -----------------
"MainThread" #26 prio=5 tid=0x00007fdaeb00e200 nid=27395 runnable [0x0000000000000000]
   java.lang.Thread.State: RUNNABLE
   JavaThread state: _thread_in_java
0x0000000113c59999 * java.lang.StringUTF16.compress(char[], int, int) bci:1 line:223 (Compiled frame; information may be imprecise)
                   * java.lang.String.<init>(char[], int, int, java.lang.Void) bci:36 line:5129 (Compiled frame; information may be imprecise)
                   * java.lang.String.<init>(char[]) bci:6 line:315 (Compiled frame; information may be imprecise)
                   * ECoreIndexOf.exhaustive(boolean, boolean, java.nio.charset.Charset, java.nio.charset.Charset) bci:130 line:320 (Compiled frame)
                   * ECoreIndexOf.main(java.lang.String[]) bci:678 line:142 (Interpreted frame)
                   * java.lang.invoke.LambdaForm$DMH+0x000000011a041000.invokeStatic(java.lang.Object, java.lang.Object) bci:10 (Interpreted frame)
                   * java.lang.invoke.LambdaForm$MH+0x000000011a042400.invoke(java.lang.Object, java.lang.Object, java.lang.Object) bci:33 (Interpreted frame)
                   * java.lang.invoke.Invokers$Holder.invokeExact_MT(java.lang.Object, java.lang.Object, java.lang.Object, java.lang.Object) bci:20 (Interpreted frame)
                   * jdk.internal.reflect.DirectMethodHandleAccessor.invokeImpl(java.lang.Object, java.lang.Object[]) bci:55 line:155 (Interpreted frame)
                   * jdk.internal.reflect.DirectMethodHandleAccessor.invoke(java.lang.Object, java.lang.Object[]) bci:23 line:104 (Interpreted frame)
                   * java.lang.reflect.Method.invoke(java.lang.Object, java.lang.Object[]) bci:102 line:565 (Interpreted frame)
                   * com.sun.javatest.regtest.agent.MainWrapper$MainTask.run() bci:134 line:138 (Interpreted frame)
                   * java.lang.Thread.runWith(java.lang.Object, java.lang.Runnable) bci:5 line:1529 (Interpreted frame)
                   * java.lang.Thread.run() bci:19 line:1516 (Interpreted frame)
0x0000000113b625a0 <StubRoutines (initial stubs)>
0x000000010a21ac53 __ZN9JavaCalls11call_helperEP9JavaValueRK12methodHandleP17JavaCallArgumentsP10JavaThread + 0x2e3
0x000000010a219cee __ZN9JavaCalls12call_virtualEP9JavaValueP5KlassP6SymbolS5_P17JavaCallArgumentsP10JavaThread + 0x14e
0x000000010a219db3 __ZN9JavaCalls12call_virtualEP9JavaValue6HandleP5KlassP6SymbolS6_P10JavaThread + 0x63
0x000000010a2ef2d5 __ZL12thread_entryP10JavaThreadS0_ + 0x95
0x000000010a22d654 __ZN10JavaThread17thread_main_innerEv + 0x94
0x000000010a7b4e48 __ZN6Thread8call_runEv + 0xa8
0x000000010a5cec5f __ZL19thread_native_entryP6Thread + 0x10f

We then saw a series of timeouts, or timed-out then completed:

TEST: java/lang/StringBuffer/ECoreIndexOf.java#id0
TEST RESULT: Error. test was interrupted! (timeout?)

TEST: java/lang/String/UnicodeCasingTest.java
TEST RESULT: Error. "main" action timed out with a timeout of 800 seconds on agent 31

TEST: java/lang/StringBuilder/Comparison.java
TEST RESULT: Error. "testng" action timed out with a timeout of 480 seconds on agent 38; but completed after timeout - suppressed status: "Passed. Execution successful"

TEST: java/lang/String/CompactString/MaxSizeUTF16String.java
TEST RESULT: Error. '/System/Volumes/Data/mesos/work_dir/jib-master/install/jdk-27+5-368/macosx-x64.jdk/jdk-27.jdk/Contents/Home/bin/java' timed out after 1920000 ms (elapsed time including timeout handling 4404936 ms); but completed after timeout - suppressed status: "Passed."

TEST: java/lang/StringBuilder/CompactStringBuilder.java
TEST RESULT: Error. '/System/Volumes/Data/mesos/work_dir/jib-master/install/jdk-27+5-368/macosx-x64.jdk/jdk-27.jdk/Contents/Home/bin/java' timed out after 1920000 ms (elapsed time including timeout handling 4221571 ms); but completed after timeout - suppressed status: "Passed."

I suspect the timeout handling actions may have been running concurrently with, and so interfered with, the other tests.

But also see JDK-8366583