CondVar is slower than std version

[chenfengyuan]

code use parking_lot
code use std

After cargo build -r and run, I have below results.

version	duration
parking_lot	34.016281622s
std	6.342443319s

Version:
rust 1.79.0
parking_lot v0.12.3

Benchmark results:
rust 1.79.0
commit id ca920b3
cargo run --bin mutex --release -- 9:36:9 5 5 2 2

- Running with 9 threads
- 5 iterations inside lock, 5 iterations outside lock
- 2 seconds per test
        name         |    average     |     median     |    std.dev.
parking_lot::Mutex   |    688.961 kHz |    686.070 kHz |    157.593 kHz
std::sync::Mutex     |   1056.229 kHz |   1066.855 kHz |     60.092 kHz
pthread_mutex_t      |   1472.396 kHz |   1442.833 kHz |    138.366 kHz
- Running with 18 threads
        name         |    average     |     median     |    std.dev.
parking_lot::Mutex   |     48.460 kHz |     48.602 kHz |      4.002 kHz
std::sync::Mutex     |    521.675 kHz |    530.139 kHz |     28.304 kHz
pthread_mutex_t      |    734.650 kHz |    731.346 kHz |     38.607 kHz
- Running with 27 threads
        name         |    average     |     median     |    std.dev.
parking_lot::Mutex   |     24.781 kHz |     24.858 kHz |      0.475 kHz
std::sync::Mutex     |    340.293 kHz |    341.380 kHz |     21.122 kHz
pthread_mutex_t      |    485.667 kHz |    484.665 kHz |     25.619 kHz
- Running with 36 threads
        name         |    average     |     median     |    std.dev.
parking_lot::Mutex   |     18.455 kHz |     19.806 kHz |      1.716 kHz
std::sync::Mutex     |    255.091 kHz |    256.855 kHz |     16.656 kHz
pthread_mutex_t      |    362.141 kHz |    360.492 kHz |     23.749 kHz